Non-Vascular Plants Lecture Slides PDF

BIOL 156 NON-VASCULAR PLANTS ALFRED K. APETORGBOR  COURSE OUTLINE General features, classification, structure, reproduction and life cycles of Thallophytes and Bryophytes. Evolution, economic importance, distribution and ecology of Thallophytes and Bryophytes and their adver...

BIOL 156 NON-VASCULAR PLANTS ALFRED K. APETORGBOR  COURSE OUTLINE General features, classification, structure, reproduction and life cycles of Thallophytes and Bryophytes. Evolution, economic importance, distribution and ecology of Thallophytes and Bryophytes and their adverse environmental impact.  OBJECTIVES Distinguish the characteristics of Non-vascular and Vascular plants and their life cycles. Distinguish between the various groups of Non- vascular plants - algae, liverworts, hornworts and mosses.  SOME READING MATERIALS 1. A. C. Dutta: Botany for Degree Students 2. Peter R. Bell: Green Plants: Their Origin and Diversity 3. William T. Doyle: Non-vascular Plants: Form and Function 4. F. E. Round: Introduction to the Lower Plants 5. Philip Sze: A Biology of the Algae 6. Kingsley R. Stern: Introductory Plant Biology NON-VASCULAR PLANTS ALFRED K. APETORGBOR  DIVISIONS OF THE PLANT KINGDOM The Plant Kingdom is divided into two main groups: i. CRYPTOGAMS (flowerless or seedless plants) ii. PHANEROGAMS (flowering or seed- bearing plants) or SPERMATOPHYTA  The Cryptogams form three main groups: Thallophyta, Bryophyta and Pteridophyta Thallophyta are characterized by: ✓ Undifferentiated thallus that has no roots, stems or leaves ✓ Are single-celled or simple multicellular plants ✓ Include Algae and Fungi  Bryophyta are simple plants with stems and leaves but lack true roots ✓Include the Mosses, Liverworts and the Hornworts Pteridophyta have stems, leaves, true roots and vascular system but lack flowers/seeds Include the Ferns and their allies.  PHANEROGAMS (SPERMATOPHYTA) have flowers which produce seeds ✓Consist of Gymnosperms (naked- seeded plants) eg. Cycads and Conifers, and Angiosperms (closed- seeded plants)  PLANT KINGDOM CRYPTOGAMS PHANEROGAMS/ SPERMATOPHYTA THALLOPHYTA BRYOPHYTA PTERIDOPHYTA GYMNOSPERMA ANGIOSPERMA MONOCOTS DICOTS FUNGI ALGAE MOSSES LIVERWORTS HORNWORTS  Angiosperms are further divided into ✓ Dicotyledons (have embryos with two cotyledons) and, ✓ Monocotyledons (have embryos with one cotyledon). ▪ Thallophyta (Fungi and Algae) and Bryophyta are described as NON- VASCULAR ✓because they do not have specialized internal tissues (xylem and phloem) for conveyance of materials (water, mineral salts and food) from one part of the body to the other. ▪Pteridophyta, Gymnospermae and Angiospermae are described as VASCULAR (or TRACHEOPHYTES) ✓because they have specialized vascular tissues (phloem and xylem) in most of their organs ALGAE  ALGAE CLASSIFICATION For many years it has been customary to classify algae according to their colour Therefore, we speak of green, brown, golden-brown, red algae, etc. All algae contain at least one type of chlorophyll, but they also contain other types of pigments and these may mask the colour of the chlorophyll  ALGAE Cont’d Unicellular motile algae are grouped by some biologists along with some multicellular, motile animals, in a separate kingdom (neither plant nor animal, but including attributes of both) called the Protista  Usually movement by algae cells is produced by the beating action against the water of one or more of the protoplasmic extensions from the cell called cilia or flagella PRIMARY CLASSIFICATION OF THE ALGAE Algae are basically classified into the following Divisions/Phyla: ✓ Cyanophyta (Blue-green algae) ✓ Chlorophyta (Green algae) ✓ Bacillariophyta (Diatoms) ✓ Phaeophyta (Brown algae) ✓ Rhodophyta (Red algae) ✓ Euglenophyta (Euglenoids) ✓ Chrysophyta (Golden algae)  CLASSIFICATION Cont’d In general details of vegetative structure and processes of reproduction are not particularly useful for the primary classification of algae Instead, the primary classification is based on five criteria of a different nature:  CLASSIFICATION Cont’d 1. Photosynthetic pigments 2. Nature of the food reserve 3. Nature of the cell wall component 4. Types of flagella 5. Details of cell structure  The final classification of the algae depends on a combination of several characteristics and not on any one single feature  1. PHOTOSYNTHETIC PIGMENTS Algae from the various Phyla/Divisions show striking differences in colour And these often afford a quick guide to the preliminary classification of an alga However the colour frequently varies with changes in environmental conditions  And an accurate classification depends on the chemical analysis of the photosynthetic pigments The distribution of these pigments is important in algal classification  There are three kinds of photosynthetic pigments in algae These are ✓ the chlorophylls ✓ the carotenoids, and ✓ the biloproteins  i. CHLOROPHYLLS Chlorophylls extracted from different algae show different spectral properties On the basis of this a number of different chlorophylls have been recognized and termed chlorophyll a, b, c, d and e  The distribution of these chlorophylls among various algal groups is what results in the differences in colour Chlorophyll a is present in all algae as it is in all photosynthetic organisms except the photosynthetic bacteria Chlorophyll b, the other chlorophyll of higher plants, is found in the Euglenophyta and the Chlorophyta ✓ They are not found in any other algal division Chlorophyll c is present in members of the Chrysophyta, Bacillariophyta, Cryptophyta and the Phaeophyta Chlorophyll d appears to be present only in the Rhodophyta Chlorophyll e has been identified in only two species of the Xanthophyta  ii. CAROTENOIDS Carotenoids are of two kinds: ✓Carotenes, and ✓ Xanthophylls Carotenes are linear unsaturated hydrocarbons, and Xanthophylls are oxygenated derivatives of the carotenes  Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms. The term "unsaturated“ means more hydrogen atoms may be added to the hydrocarbon to make it saturated (i.e. consisting of all single bonds).  CAROTENOIDS Cont’d β-carotenes are present in most algae although they are replaced by α- carotenes in some members of the Chlorophyta and Cryptophyta and to a lesser extent in the Rhodophyta In the Chlorophyceae β-carotene is replaced by two carotenes which are characteristic of photosynthetic bacteria: lycopene and γ-carotene  CAROTENOIDS Cont’d There are many different Xanthophylls in algae, and since many are unique to particular algal groups, they are important diagnostic features in the classification of algae  iii. BILOPROTEINS Chlorophylls and Carotenoids are soluble in lipid solvents and cannot be extracted in aqueous solution However, water soluble pigments can be extracted from some types of algae These were called Phycobilins During the extraction procedure the free pigment cannot be separated from the protein part  BILOPROTEINS Cont’d And the name of the pigment was therefore changed from Phycobilins to Biloproteins to indicate the existence of the pigment-protein complex Biloproteins are present in only three algal divisions: ✓the Cyanophyta ✓the Rhodophyta, and ✓ the Cryptophyta  BILOPROTEINS Cont’d Analysis of the spectral properties of these pigments shows that there are two kinds of Biloproteins: Phycocyanin and Phycoerythrin Each of these biloproteins shows differences among the three groups of algae  BILOPROTEINS Cont’d Cont’d In general those of the Cyanophyta are of the C-type Those of the Rhodophyta are of the R-type, and Those of the Cryptophyta are of a third type  PHOTOSYNTHETIC PIGMENTS Cont’d The proportion of one kind of photosynthetic pigment to the other is variable For example cells of the Chlorophyta and Euglenophyta appear green because of an excess of chlorophylls over carotenoids  PHOTOSYNTHETIC PIGMENTS Cont’d Whereas the yellow-brown colour of groups such as the Pyrrophyta, Chrysophyta, Cryptophyta, Phaeophyta, etc. and the yellow- green colour of the Xanthophyta reflects an excess of carotenoids compared with chlorophylls  PHOTOSYNTHETIC PIGMENTS Cont’d Also, the characteristic colour of the Cyanophyta (blue-green) and the Rhodophyta (red) are due to an excess of the appropriate biloproteins PHOTOSYNTHETIC PIGMENTS Cont’d However the proportion of one type of pigment to the other can vary considerably with changes in the environmental conditions And it is difficult to justify its use as a taxonomic feature  2. FOOD STORAGE The initial stages of CO2 fixation are probably the same in all photosynthetic organisms Thus, the primary products of photosynthesis are the same in all algae However, the insoluble products which accumulate over a longer period of time are more variable and they afford useful taxonomic criteria  FOOD STORAGE Cont’d The compounds which are most widespread and most useful in the primary classification of algae are various polysaccharides “True” starch, similar to that found in higher plants, is only found in one algal division, the Chlorophyta Two other divisions, the Rhodophyta and the Cyanophyta, accumulate characteristic starches:  FOOD STORAGE Cont’d ✓Floridean starch and Myxophycean starch respectively Both are polyglucose molecules identical to the amylopectin part of higher plant starch In some other algae such as the Phaeophyta, the storage carbohydrate is Laminarin Paramylum is present in the Euglenophyta  3. CELL WALL COMPONENT When a cell wall is present in an alga its chemical constituent varies from one group to the other And these are sometimes important indications of the taxonomic position of the particular alga  CELL WALL COMPONENT Cont’d The cell wall is generally made up of two kinds of materials: ✓ an inner water insoluble material, and ✓ an outer pectic or mucilageneous substance soluble in boiling water Although both inner and outer wall materials are mainly polysaccharides, lipid and proteinaceous materials are also present  CELL WALL COMPONENT Cont’d The commonest water insoluble polysaccharide of the inner layer is cellulose And this is present in walled species of all divisions except the Chrysophyta Other characteristic components of the cell wall includes polyuronic acid and alginic acid  4. TYPE OF FLAGELLA Apart from the Cyanophyta and the Rhodophyta flagella are found in other divisions of the algae And their nature, number and position are important characters for the primary classification of the algae  FLAGELLA Cont’d The detailed fibrillar structure of the algal flagella in transverse section resembles that of cilia and flagella of other organisms in showing a typical 9+2 pattern of component fibrils  FLAGELLA Cont’d Each flagellum is bounded by an extension of the plasmalemma (plasma membrane) Within the plasmalemma there is a ring of nine pairs of fused fibrils/tubules and a pair of unfused fibrils/tubules at the centre This is the basic pattern of all plant and animal flagella  FLAGELLA Cont’d The macrostructure of the flagellum does not however show such uniformity For a long time algal flagella were thought to be of two kinds: ✓the acronematic (smooth), and ✓the pantonematic/pleuronematic (flimmer)  FLAGELLA Cont’d The acronematic type is smooth and whiplike while the pantonematic/pleuronematic type has longitudinal rows of fine hairs (flimmers or mastigonemata/ mastigonemes) arranged along the axis of the flagella  FLAGELLA Cont’d More recent work with the electron microscope has revealed one other type of flagella in which the flagella surface is covered with minute hairs (different from those of the pantonematic/pleuronematic flagella) and scales  5. DETAILS OF CELL STRUCTURE The important structural features of the cell of various algae normally are uniform throughout the division In most texts particularly on the Chlorophyta, chloroplast runs throughout the entire division while chromatophores are found in others  CELL STRUCTURE Cont’d The distinction between these two pigments is generally based on the differences of pigmentation The term chloroplast is used in species of algae possessing chlorophylls a and b (as in higher plants) And the term chromatophore is applied to algal species not having chlorophyll b, but having an excess of carotenoids over chlorophylls  CELL STRUCTURE Cont’d The position of chloroplast in the cell is very important They are termed parietal when located towards the periphery of the cell, and axiel when located towards the centre  CELL STRUCTURE Cont’d A further feature of the chloroplast which is emphasized is the presence or absence of a deeply staining area of the chloroplast generally associated with deposits of reserved products, the pyrenoid  CELL STRUCTURE Cont’d The cells of archegonate plants (plants having archegonia as female reproductive part eg. Bryophytes) normally have numerous discoid chloroplasts, and the possession of such a feature by some algal cells is therefore emphasized  MORPHOLOGIC DIVERSITY OF THE ALGAE The body of an alga is a thallus - plant body not differentiated into stem, leaves, and lacks true roots and vascular system Algae range in form from Unicellular through Colonial, Filamentous, Siphonaceous, to the complex Parenchymatous thalli of the larger seaweeds UNICELLULAR FORMS  UNICELLULAR FORMS Unicellular forms are among all groups of algae except the Rhodophyta and Phaeophyta, although even among these two groups unicellular stages are produced at various points in their life history The unicellular species may be motile (flagellated), non-motile (coccoid/spherical) or amoeba-like  UNICELLULAR FORMS Cont’d Flagellated solitary cells are considered primitive in most groups of eukaryotic algae and are believed to have given rise to the other types They vary in the number and arrangement of the flagella MULTICELLULAR FORMS  1. COLONIAL FORMS The association of organisms into groups of cells or colonies probably originated as it does in ontogeny (development of the individual) ✓by the failure of the cells to separate after cell division  i. COENOBIAL In this type of thallus the cells are either embedded in mucilaginous matrix or united by a more localized production of mucilage It is not merely an irregular aggregation of cells but it is a well defined colony with important reproductive features  COENOBIAL Cont’d The coenobium (colony) is of constant size and shape for any given species and the cells show no vegetative division Thus, the number of cells of a coenobium is determined at its formation and does not increase during growth of the colony eg. Volvox  ii. AGGREGATIONS Unlike the coenobium an aggregation of cells is not of constant size and shape Moreover, vegetative cell division takes place so there is an increase in cell number during growth The most common type of aggregation is the palmelloid form in which the cells are embedded/envelopped in an irregular mass of mucilage  AGGREGATION Cont’d The dendroid colony consists of cells which are united by localized production of mucilage to form a tree-like structure Another kind is the rhizopodial form of aggregation consisting of variable number of amoeboid cells joined together by a number of cytoplasmic processes  2. FILAMENTOUS FORMS Filamentous forms are also characterized by vegetative cell division but unlike the irregular aggregations the cells are arranged in linear rows with adjacent cells sharing a common cross wall Cytoplamic connections (plasmodesmata) may extend through the cross walls  FILAMENTOUS FORMS Cont’d In uniseriate filaments the cells are arranged in a single series Multiseriate filaments have more than one series of cells but still retain a thread-like appearance  FILAMENTOUS FORMS Cont’d Filaments may be branched or unbranched More complex filamentous algae may show differentiation among the branches Heterotrichous filaments have a distinct system of prostrate branches growing attached to the substrate and an erect system of more open branches extending free of the substrate  FILAMENTOUS FORMS Cont’d In the pseudoparenchymatous thalli the branches do not spread apart in an open branching pattern but form a compact mass that makes individual branches difficult to see Such a structure is the basis of all larger members of the Rhodophyta  3. SIPHONEOUS/SIPHONACEOUS FORMS In this kind, the thallus is multinucleate but is not divided into cells apart from those associated with reproduction The thallus is not divided up by septa, ie. the many/numerous nuclei are not compartmentalized into cells. The thallus can be extremely elaborate and is generally considered more desirable to refer to such a thallus as acellular and not unicellular  4. PARENCHYMATOUS FORMS Vegetative cell division in filamentous forms occurs in one plane only so that a single row of cells is formed When cells divide in more than one plane a parenchymatous construction is produced Cell divisions in three dimensions produce a solid mass of cells rather than the threadlike linear arrangement of a filament  PARENCHYMENTOUS Cont’d Parenchymatous thalli may be blades, branching cylinders or hollow tubes The parenchymatous construction which is also characteristic of bryophytes and vascular plants is the most advanced form  PARENCHYMENTOUS Cont’d Growth of the filamentous and parenchymatous thalli can be: Diffused ie. all the cells are capable of division Apical ie. one or more well defined apical cells dividing to give the remainder of the thallus  PARENCHYMENTOUS Cont’d Trichothallic ie. a specialized meristematic region at the base of branches or filaments, or Intercalary ie. well defined dividing regions are not located terminally  METHODS OF REPRODUCTION IN THE ALGAE A particular plant may take to one or more of the three methods of reproduction, ie. ✓Vegetative ✓Asexual, or ✓Sexual  1. VEGETATIVE REPRODUCTION Vegetative reproduction commonly takes place by cell division or by fragmentation Many filamentous algae reproduce vegetatively by the fragmentation of the filament to liberate small pieces Among filamentous members of the Cyanophyta this is a specialized process and a number of short motile lengths of filaments are formed  VEGETATIVE REPRODUCTION Cont’d These entities are referred to as hormogonia They are short segments from the ends of the filaments that form when the walls between the cells split or when the cell in between dies  2. ASEXUAL REPRODUCTION Asexual reproduction involves the formation of reproductive cells that develop directly into new individuals (without sexual fusion) This is normally achieved by the formation of spores of various kinds Most groups except the Cyanophyta and Rhodophyta produce zoospores which are motile unicells  ASEXUAL REPRODUCTION Cont’d Non-motile asexual spores are also produced and these are called aplanospores When the non-motile asexual spores appear identical to the parent cell (ie. similar in form but a miniature of the parent cell) they are referred to as autospores  ASEXUAL REPRODUCTION Cont’d And if they acquire a thick wall around them, they are referred to as hypnospores The term ‘‘swarmer’’ is commonly used for any motile cell formed when a vegetative cell reproduces, and (it indicates that) it is unknown whether the swarmer behaves as a gamete or a zoospore  ASEXUAL REPRODUCTION Cont’d Among multicellular forms the spore may be formed in all vegetative cells, or their formation may be restricted to well-defined sporangia In the Phaeophyta two specialized kinds of sporangia can be recognized These are the plurilocular and the unilocular sporangia  ASEXUAL REPRODUCTION Cont’d The plurilocular consists of an enlarged vegetative cell which divides into a number of compartments and the content of each compartment develops into a swarmer  ASEXUAL REPRODUCTION Cont’d In the unilocular type contents of the enlarged vegetative cell divide to form a number of swarmers without any previous division of the parent cell into a number of compartments Swarmers from the unilocular type are always asexual whereas either gametes or zoospores can be liberated from the plurilocular sporangia  3. SEXUAL REPRODUCTION In sexual reproduction the cells released by the parents are gametes Pairs of compatible gametes fuse to form a zygote Sexual reproduction is achieved by three basic means: ✓Isogamy ✓Anisogamy, and ✓Oogamy  SEXUAL REPRODUCTION Cont’d If both gametes of a pair are flagellated and similar in size, they are isogametes Gametes that are flagellated but differ in size are known as anisogametes Isogamy involves the fusion of two identical gametes and anisogamy is the fusion of two morphologically dissimilar gametes  SEXUAL REPRODUCTION Cont’d Sometimes morphologically identical gametes behave differently and so show physiological anisogamy In oogamy only one gamete (the sperm) is flagellated, and it fuses with a larger non-flagellated gamete (the egg)  SEXUAL REPRODUCTION Cont’d Oogamy also differs from anisogamy in that the female gamete (the egg) is not liberated prior to fertilization but is fertilized while within the oogonium  GERMINATION OF THE ZYGOTE The zygote formed by the three methods of sexual reproduction has an independent existence for a variable length of time Upon germination the content of the zygote divides to form a number of zoospores  ZYGOTE GERMINATION Cont’d These are liberated and after a period of swimming they germinate into a parent plant More seldom the zygote germinates directly into the adult plant During growth an alga passes through a number of distinct phases and the sequence of these is known as its life history  ZYGOTE GERMINATION Cont’d The life history has two aspects: ✓the somatic or morphological, and ✓the cytological The somatic or morphological aspect involves whether in the life history the vegetative stages are morphologically alike or not  ZYGOTE GERMINATION Cont’d The cytological aspect is usually concerned with the chromosome number of each particular stage The type of life history thought to be most primitive is that in which the only vegetative stage is haploid and the zygote represents the only diploid stage (A)  ZYGOTE GERMINATION Cont’d The opposite extreme is that in which the vegetative stage is diploid and in which the gametes represent the only haploid stage (B) Intermediate between the two extremes are those life histories in which there is an alternation between two vegetative stages, one haploid and the other diploid (C)  ZYGOTE GERMINATION Cont’d When the two stages are morphologically similar the alternation is isomorphic, and When they are morphologically different the alternation is heteromorphic PROKARYOTIC ALGAE  DIVISION CYANOPHYTA (Blue-green Algae) These are a small group of primitive algae characterized by presence of a blue-green pigment, PHYCOCYANIN, in addition to chlorophyll (together giving a blue-green colour)  CYANOPHYTA Cont’d Some species are truly unicellular, while in others, the daughter cells after divisions adhere together to form a chain of cells (filament) or a flat or spherical colony A great majority of them are freshwater dwellers and are often found in almost every stagnant pool, wet ground or in the form of road slime after rains  CYANOPHYTA Cont’d The cell structure is a primitive type There is no definite nucleus or any plastid, and the protoplast is differentiated into: ✓ a peripheral coloured zone – the CHROMOPLASM, and ✓an inner colourless portion – the CENTRAL BODY  CYANOPHYTA Cont’d The cell wall is made of cellulose and pectic compounds Carbohydrate occurs in the form of glycogen, starch being altogether absent A gelatinous sheath is a common feature in most of them Some filamentous forms, particularly Oscillatoria, exhibit a slow, spontaneous movement  CYANOPHYTA Cont’d Blue-green algae never reproduce sexually, nor do they bear any kind of ciliated body The common types of vegetative reproduction are: ✓cell division in unicellular forms ✓breaking up of the colony in colonial forms ✓fragmentation of the filament into short pieces called HORMOGONIA in filamentous forms  CYANOPHYTA Cont’d In some filamentous forms (except Oscillatoria), a vegetative cell may act as a resting spore called AKINETE AKINETES are thick-walled cells formed after a period of active growth that survive in a dormant state when conditions are unfavorable for further growth  CYANOPHYTA Cont’d They may be produced singly or in a chainThey are larger than vegetative cells and have thick walls and granular cytoplasm with an abundance of cyanophycin granules The cell wall is indistinct from that of the mother cell  CYANOPHYTA Cont’d They may remain inactive for many years At germination the protoplast is released by rupture of the wall or through a pore before growth commences  CYANOPHYTA Cont’d One or more enlarged vegetative cells with transparent contents and thickened walls may be present in the filamentous forms These are called HETEROCYSTS HETEROCYSTS are specialized cells for nitrogen fixation  CYANOPHYTA Cont’d When dissolved nitrogen compounds are low in the surrounding water, some vegetative cells differentiate into heterocysts In the process, N2 from the air is converted to ammonium  CYANOPHYTA Cont’d During differentiation additional walls are added to the wall and pores through the wall connect heterocysts to other vegetative cells Heterocysts are usually larger than vegetative cells, have light yellow- green colour from loss of their (phyco)biliproteins, and lack storage granules  SOME MEMBERS OF THE CYANOPHYTA Gloeocapsa Oscillatoria Nostoc Anabaena Rivularia Lyngbya  MEMBERS OF THE CYANOPHYTA Cont’d Gloeocapsa: Always unicellular, but often, 2 to 4, or sometimes several daughter cells are held together in a colony by a mucilagenous sheath Oscillatoria: Consists of a slender, unbranched, cylindrical filament Each filament is made up of numerous short cells.  MEMBERS OF THE CYANOPHYTA Cont’d All the cells are alike except the end cell. This is usually convex and the filament is not differentiated into base and apex. When a sheath is present as in Lyngbya, the term TRICHOME refers to the series of cells only, while the filament includes the sheath and cells.  MEMBERS OF THE CYANOPHYTA Cont’d Lyngbya: Is similar to Oscillatoria, but its filaments have a firm mucilaginous sheath that normally extends beyond the terminal cell Nostoc and Anabaena: Both are characterized by unbranched filamentous forms made of beaded cells and the presence of heterocysts  MEMBERS OF THE CYANOPHYTA Cont’d They differ in the following respects: ✓Nostoc filaments are twisted and flexuous, forming a tangled mass and have a thick (but not very firm) sheath ✓Anabaena filaments are straight or slightly curved, more rigid, often free and with a thin sheath  Nostoc and Anabaena Cont’d ✓Nostoc filaments often lie embedded in more or less firm gelatinous matrix, while Anabaena filaments are often free or sometimes in a thin gelatin ✓In Nostoc the heterocysts are intercalary as well as apical, while in Anabaena they are only intercalary ✓Akinetes are more frequent and much more elongated in Anabaena than in Nostoc  Nostoc and Anabaena Cont’d ✓Nostoc is equally terrestrial and aquatic, while Anabaena is mostly aquatic Some species of Nostoc are symbiotic and live within the tissues of land plants (eg. in the thallus of Anthoceros spp.), or are the algal partner in some lichens. EUKARYOTIC ALGAE  DIVISION CHLOROPHYTA (Green algae) They are characterized by the presence of chlorophyll located in definite plastids (chloroplasts) They are mostly freshwater algae, but some species are terrestrial They exhibit a variety of forms: ✓Unicellular or colonial - being motile or non-motile  CHLOROPHYTA Cont’d Multicellular - being thalloid or filamentous Coenocytic (colony of constant size) The protoplast is well organized, having a definite nucleus (usually one in each cell or several in a coenocyte), and one or more distinct chloroplasts  CHLOROPHYTA Cont’d The chloroplasts contain one or more pyrenoids (rounded protein bodies surrounded by a starchy envelope) The cell wall is made of cellulose and often has a layer of pectose around it Gelatinous sheath may or may not be present  CHLOROPHYTA Cont’d Most unicellular and colonial forms are provided with whip-like structures called FLAGELLA/CILIA – often 2, sometimes 4 or many – for motility of cells or colonies The flagella/cilia are of uniform length and always formed at the anterior end of the cell  CHLOROPHYTA Cont’d In higher forms of Chlorophyta the flagella/cilia are restricted to the reproductive bodies – zoospores and zoogametes Primitive forms have two or more contractile vacuoles and a small eyespot  REPRODUCTION Vegetative reproduction takes place by cell division or fragmentation Asexual reproduction takes place by spores of various types: ✓A motile, ciliate spore (zoospore)  REPRODUCTION Cont’d ✓A non-motile, non-ciliate spore with a distinct wall of its own but produces within a mother cell (APLANOSPORE) A vegetative cell acting as a spore, having no wall of its own – the wall of the mother cell acting as the wall of the spore (AKINETE)  REPRODUCTION Cont’d Sexual reproduction takes place by isogamy, anisogamy or oogamy depending on the species Whatever the mode of sexual reproduction, some species are:  REPRODUCTION Cont’d ✓HOMOTHALLIC (ie. the pairing gametes come from the same parent), while others are ✓HETEROTHALLIC (ie. the pairing gametes come from two separate parents  REPRODUCTION Cont’d In many green algae, it has been observed that a gamete can grow PARTHENOGENECALLY (ie. without fusion with another gamete) into a new plant The gamete thus behaves as a spore and is called a PARTHENOSPORE or AZYGOSPORE  REPRODUCTION Cont’d Sometimes, as in Spirogyra, the gamete has no cilia/flagella and is called APLANOGAMETE  ORIGIN AND EVOLUTION OF SEXUALITY IN THE CHLOROPHYTA The vegetative method of reproduction is the most primitive method of multiplication of individual plants Asexual reproduction by zoospores appeared later in the lower Chlorophyta possibly as a means of rapid multiplication ORIGIN AND EVOLUTION OF SEXUALITY Cont’d Sexual reproduction appeared later, and still continued right up to the highest division of the plant kingdom ✓ evidently to achieve something that was not possible by the other methods  SEXUALITY IN THE CHLOROPHYTA Cont’d That something is protection, ✓for the thick-walled zygote – the result of the sexual act – is better equipped to withstand environmental conditions before it starts a new life  SEXUALITY IN THE CHLOROPHYTA Cont’d Sexual reproduction has other advantages too: ✓When conditions are favourable for vegetative activity, neither spores nor gametes are produced ✓When conditions are less favourable, sexual cells or spores are produced  SEXUALITY IN THE CHLOROPHYTA Cont’d ✓As the plant approaches the end of its life or when conditions are very unfavourable, sexual cells or gametes are produced The mode of reproduction is thus, greatly influenced by the changing environment and age of the plant  SEXUALITY IN THE CHLOROPHYTA Cont’d The origin of sexuality in the Chlorophyta appeared as a modification of the older asexual method And is directly correlated with the origin of sexual cells or gametes from asexual cells or spores (zoospores)  SEXUALITY IN THE CHLOROPHYTA Cont’d Because of their small size (owing to repeated divisions) ✓The gametes have lost the power of functioning individually They have thus, developed some kind of mutual attraction and freely come together in pairs and fuse together This is the earliest indication of sexuality  SEXUALITY IN THE CHLOROPHYTA Cont’d It may then be rightly said that gametes are derived from spores (zoospores) It is also seen that spores and gametes are similar in several members of the Chlorophyta ✓eg. in Chlamydomonas, Ulothrix, and Oedogonium, except that the gametes are smaller and more numerous  SEXUALITY IN THE CHLOROPHYTA Cont’d Once sexuality appeared, it established itself and its evolution through isogamy to anisogamy to oogamy, based on the differentiation of sexual cells and sexual organs, proceeds towards a high degree of complexity, possibly towards a state of perfection through successive stages  SEXUALITY IN THE CHLOROPHYTA Cont’d In the simple and primitive forms of Chlorophyta, there is fusion of two gametes (zoogametes) similar in shape and size This is called ISOGAMY as found in Chlamydomonas, Ulothrix, etc. The next stage in the evolution of sexuality is ANISOGAMY, as found in Pandorina, certain species of Chlamydomonas, etc. SEXUALITY IN THE CHLOROPHYTA Cont’d Here, a slight difference is noticed in the size of the gametes or in their behaviour: the first indication of differentiation into male and female A complete differentiation of gametes and gametangia into male and female is found in the advanced forms of the Chlorophyta  SEXUALITY IN THE CHLOROPHYTA Cont’d The union of such differentiated gametes is called OOGAMY, as found in Oedogonium, Vaucheria, etc. In all the Chlorophyta, however, the gametangia are single-celled  EXAMPLES OF MEMBERS OF THE CHLOROPHYTA Chlamydomonas Zygnema Pandorina Oedogonium Eudorina Vaucheria Ulothrix Caulerpa Chaetophora Chara Protococcus Spirogyra DIVISION EUGLENOPHYTA (Euglenoids) Euglena is a most simple, unicellular organism The evolution of the higher forms of plants possibly started from it It grows in large numbers in polluted water containing organic substances and colours it green  EUGLENOPHYTA Cont’d It is a single-celled, naked, free- swimming organism It has a single flagellum, ie. a long, slender, whip-like projection, which vibrates and helps the plant to swim It can also crawl by changing its shape  EUGLENOPHYTA Cont’d The protoplast contains a central nucleus, several green plastids, a contractile vacuole and an eyespot near the blunt end  DIVISION PHAEOPHYTA (Brown Algae) These are a group of seaweeds with a variety of peculiar forms and sizes They are widely distributed between tidal levels along sea coasts predominantly of temperate seas They are attached to rocks or some other substrata  PHAEOPHYTA Cont’d In colder seas they seldom go beyond a depth of 20m While in warmer seas, a few species may grow up to a maximum depth of 90m Some also grow as epiphytes on or as endophytes in other algae A few are free-floating  PHAEOPHYTA Cont’d Their colour ranges from brown to olive-green ✓due to the presence in the chloroplast of a brown pigment FUCOXANTHIN, which masks the chlorophyll There are no pyrenoids The reserve food may be ✓a kind of sugar (and not starch) ✓or, more commonly, a complex carbohydrate called LAMINARIN  PHAEOPHYTA Cont’d Some like Ectocarpus are short filaments While others, like Fucus and Sargassum, are usually a few cm to 1m in length Others are massive seaweeds, called GIANT KELPS (Laminaria: 2- 9m, Necrocystis: 45m, and Macrocystis: 60-90m)  PHAEOPHYTA Cont’d They grow at or below the low tide level, extending far into the sea to a depth of about 90m Small kelps are only about a meter long Unicellular brown algae are not known to exist  PHAEOPHYTA Cont’d The body of the kelp is differentiated into ✓A basal root-like, branched HOLDFAST ✓A long or short ‘stem’ called STIPE ✓And one or more leaf-like blades called FRONDS, which have air/gas bladders to facilitate floating  PHAEOPHYTA Cont’d Some species have fronds of massive size The Phyaeophyta (except Fucus and Sargassum) show a regular alternation of generation ✓ with different degrees of development of the sporophyte and the gametophyte  PHAEOPHYTA Cont’d The sporophyte and the gametophyte can be ✓ Similar (ISOMORPHIC, as in Ectocarpus) ✓Or dissimilar (HETEROMORPHIC, as in Laminaria) in external appearance  PHAEOPHYTA Cont’d And their motile cells (zoospores and gametes or sperms) are ✓laterally biciliate ✓the two flagella/cilia being of unequal lengths ✓in contrast with the apically ciliate cells of most algae  REPRODUCTION Motile reproductive bodies (zoospores and gametes or sperms) are universally present throughout the Phaeophyta Several species reproduce vegetatively by fragmentation of the thallus  REPRODUCTION Cont’d Most of them reproduce asexually, through zoospores or aplanospores (except Fucus and Sargassum) and sexually by isogamy, anisogamy or oogamy The zygote germinates without any period of rest. EXAMPLES Ectocarpus, Laminaria, Fucus, Sargassum DIVISION RHODOPHYTA (Red Algae) The Rhodophyta form a big group of highly specialized marine algae They are very widely distributed in both temperate and tropical seas, particularly in the latter  RHODOPHYTA Cont’d Many species are found between the high tide level and the low tide level along coasts ✓ a good number of species grow at depths of 60-90m, ✓ a few at much greater depths, up to 180m They are mostly attached to rocks  RHODOPHYTA Cont’d There are, however, some epiphytic and parasitic varieties which grow on other algae Although mostly marine, about 50 species have been found to occur in fresh water Red algae are characteristically red or purplish in colour due to the presence of a red pigment called PHYCOERYTHRIN which often masks the presence of chlorophyll  RHODOPHYTA Cont’d Many red algae contain a small amount PHYCOCYANIN, the blue pigment of the Cyanophyta Fresh water species are often green in colour Red algae have a variety of forms – filamentous, ribbon-shaped, distinctly leaf-like and marked with veins, etc  RHODOPHYTA Cont’d They are mostly a few to about 25cm in length, while a few are as long as 1 to 1.3m Deep-water ones are much longer Gelatinous material is abundant in the red algae, either occurring within the thallus or forming a sheath in the filamentous forms  RHODOPHYTA Cont’d Some red algae are heavily incrusted with lime The cells may be uninucleate or multinucleate with one or more plastids, which may be or without pyrenoids  RHODOPHYTA Cont’d A sugar or, more commonly, a special kind of starch called FLORIDEAN STARCH accumulates in the cells as a result of photosynthesis There is a total absence of motile ciliate cells; zoospores are altogether absent, and gametes are never ciliate  RHODOPHYTA Cont’d Members of the Rhodophyta are either haploid or they show a regular alternation of similar haploid and diploid stages, as in Polysiphonia EXAMPLES Polysiphonia, Batrachospermum  DIVISION BACILLARIOPHYTA (DIATOMS) These are commonly called DIATOMS and consist of mostly one-celled algae They are of infinite variety of forms and often of exquisite beauty The single cells may occasionally form filaments and colonies  BACILLARIOPHYTA Cont’d They are universally distributed in fresh water, as well as in salt water and also in wet ground  BACILLARIOPHYTA Cont’d In some parts of the ocean, they occur in vast assemblage as floating PLANKTON Plankton: small microscopic organisms drifting or floating in the sea or fresh water They often occur in huge numbers in a small space Most diatoms are free-floating, but some are attached by a gelatinous stalk  BACILLARIOPHYTA Cont’d The cells of diatoms have walls composed of silica Each cell wall is in two overlapping halves which are arranged exactly like the two halves of a Petri dish  BACILLARIOPHYTA Cont’d The half which overlaps the other, like the lid of a Petri dish, is the EPITHECA The other half is the HYPOTHECA Fossil diatoms have formed huge deposits of SILICEOUS or DIATOMACEOUS EARTH, often of considerable depth, in various parts of the world HUMAN AND ECOLOGICAL RELEVANCE OF THE ALGAE  BENEFICIAL ASPECTS DIATOMS (Bacillariophyta) Algae are at the bottom of aquatic food chains The whole fisheries industry depends on phytoplankton (microscopic plants) ✓and algae rank as outstanding contributors to the world food supplies Diatoms, for example, are consumed by fish that feed on plankton  Plankton: the small and microscopic organisms drifting or floating in the sea or fresh water ✓ consisting chiefly of diatoms, protozoans, small crustaceans, and the eggs and larval stages of larger animals ✓ Many animals are adapted to feed on plankton, especially by filtering the water  DIATOMS Cont’d Up to 40% of a diatom’s mass consists of oils that are converted to cod and other liver oils which are rich sources of vitamins for man The oils also may in the past have contributed to petroleum oil deposits Diatoms also have other extensive and more direct industrial uses  DIATOMS Cont’d As billions upon billions of them have reproduced and died, their microscopic glassy shells have accumulated on the ocean floor, ✓ forming deposits of DIATOMACEOUS EARTH  DIATOMS Cont’d These deposits have accumulated to depths of hundreds of metres in some parts of the world and are quarried in several areas where past geological activity has raised them above sea level Diatomaceous earth is a light, porous, and powdery looking material that contains about 6 billion diatom shells per litre  DIATOMS Cont’d It also has an exceptionally high melting point of 17500C and is insoluble in most acids and other liquids These properties make it ideal for a variety of industrial and domestic uses, including many types of filtration  DIATOMS Cont’d The sugar industry uses diatomaceous earth in sugar refinery, and its use for swimming pool filters is widespread It is also used in silver and other metal polishes, in toothpaste, and in the manufacture of paint that reflects light, which is used in highway markers and signs and on the automobile license plates It is packed as insulation around blast furnace and boilers  USES OF GREEN ALGAE Sea lettuce (Ulva sp.) has been used for food on a limited scale in Asian countries for some time and several countries are experimenting with the suitability of plankton for human consumption  USES OF GREEN ALGAE Cont’d Except for vitamin C, Chlorella contains most of the vitamins needed in nutrition and since it is also easy to culture, it may become an important protein source in many parts of the world Chlorella has also been investigated as a potential oxygen source for atomic submarine, in addition to its possible use in space  ALGIN Commercially produced ice cream, salad dressing, beer, jellybeans, latex paint, penicillin suspensions, paper, textiles, toothpaste, ceramics, and floor polish all share a common ingredient, algin, produced by the giant kelps and other brown algae  ALGIN Cont’d It is now used in so many products that one might wonder how the world used to get along without it Algin has the unique ability to regulate water behaviour in a wide variety of products  ALGIN Cont’d It can, for example, control the development of ice crystals in frozen foods, regulate the penetration of water in a porous surface, and generally stabilize any kind of suspension such as an ordinary milk- shake or other thick fluid containing water  ALGIN Cont’d It is produced by several kinds of seaweeds, but a major source is the giant kelp found in the cooler ocean waters of the world, usually just offshore where there are strong currents  MINERALS AND FOOD Brown algae also produce a number of other useful substances Many seaweeds, but particularly kelps, build up concentrations of iodine to as much as 20,000 times that of the surrounding sea water Dried kelp has been used in the treatment of goitre which results from iodine deficiency  MINERALS AND FOOD Cont’d Kelps are relatively high in nitrogen and potassium and have been used as fertilizer for many years They also have been used as source of food for fish and as livestock feed in northern Europe and elsewhere  MINERALS AND FOOD Cont’d In the Orient (Asia), many marine algae are used for food – in soup, confections, meat dishes, vegetable dishes, and beverages In Japan, there is even an industry for cultivating the red alga Porphyra in a manner comparable with more orthodox agriculture  MINERALS AND FOOD Cont’d The product is used to make a popular foodstuff In Japan, acetic acid is produced through fermentation of seaweeds Irish moss is an important edible red alga  MINERALS AND FOOD Cont’d It is used in bulking laxatives, cosmetics and pharmaceutical preparations Funori, obtained from yet another red alga, is used as a laundry starch, as an adhesive in hair dressings, and in some water-based paints  AGAR One of the most important of all algal substances is agar, produced most abundantly by the red algae Gelidium and Gracilaria This substance which has the consistency of gelatin is used (with nutrients added) around the world in laboratories  AGAR Cont’d ✓ and medical institutions as a culture medium for the growth of bacteria and fungi When various nutrients are added to it, it can also be used as a culture medium for the growth of both plant and animal cells  AGAR Cont’d Its use in making capsules containing drugs and vitamins is now worldwide It is also used as an agent in bakery products to retain moistness, as a base for cosmetics, and as an agent in the gelatin desserts to produce rapid setting  OTHER USES Current research involving red algae and other seaweeds indicates they contain a number of substances of potential medicinal value More than 20 seaweeds have been used in preparations designed for the expulsion of digestive tract worms, control of diarrhoea and the treatment of cancer  AGAR Cont’d Some have shown considerable potential as antibiotics and insecticides  DETRIMENTAL ASPECTS Plankton algae are not wholly beneficial to mankind To the waterworks engineer algae can be very troublesome Whatever the source of water to be treated (reservoirs, lakes, rivers) there is likely to be initially a considerable algal population  DETRIMENTAL ASPECTS Cont’d Much of London’s water is supplied by the River Thames, which drains a large area of agricultural land and is therefore rich in mineral salts This high salt concentration leads to prolific growth of planktonic algae much of which must be removed by filtration  DETRIMENTAL ASPECTS Cont’d One of the most abundant species is the diatom Fragilaria crotonensis and in certain seasons more than one ton by dry weight of this alga alone is removed each day Other algae, notably members of the Xanthophyta (and Myxophyta), may be far less numerous but can lend an unpleasant taste or smell to the water  DETRIMENTAL ASPECTS Cont’d In such cases filtration may be ineffective, and chlorination or absorption with activated charcoal may be necessary to make the water acceptable to the consumer On the seashore, seaweeds grow in profusion  DETRIMENTAL ASPECTS Cont’d Seaweeds are generally restricted to the coastline where the plants can be attached to a firm substratum while at the same time near enough to the surface to receive sufficient sunlight  DETRIMENTAL ASPECTS Cont’d The brown alga Sargassum natans however exists in enormous floating masses far out into the sea, and creates navigational hazard near to the West Indies in the area known as the Sargasso Sea  DETRIMENTAL ASPECTS Cont’d Pacific coast fish farmers have experienced losses of salmon and cod when dense concentrations of Chaetoceros diatoms have developed in the aquaculture pens The diatoms have long hollow spines that break off and penetrate the fish gills, disrupting gas exchange and causing bleeding  DETRIMENTAL ASPECTS Cont’d This damage in turn may permit secondary infections and excessive mucus production to occur ALGAL BLOOMS ie. massive growth of algae, may severely deplete oxygen when their cells decompose, reduce the use of lakes and streams for recreation, and interfere with water purification  DETRIMENTAL ASPECTS Cont’d Dense growth of planktonic dinoflagellates (Pyrrophyta) produce red or brown water discolourations called RED TIDES Red tides most often occur in coastal waters and estuaries  DETRIMENTAL ASPECTS Cont’d Some dinoflagellates producing red tides are luminiscent, and some contain toxins that are released into the water or accumulate in food chains In severe cases, the toxins may cause fish-kills or lead to human poisoning from eating contaminated mollusks or fishes THE BRYOPHTES GENERAL FEATURES OF BRYOPHTES  GENERAL FEATURES OF BRYOPHTES They are green land plants They possess chlorophylls A and B, starch, cellulose cellwalls and sometimes possess a cuticle The sporophyte is short-lived to annual GENERAL FEATURES OF BRYOPHYTES Cont’d The sporophyte, although photosynthetic through most of its life span preceding spore dispersal, is always attached to the gametophyte, and is at least partially dependent on it The base of the sporophyte (the foot) penetrates the tissues of the gametophyte  GENERAL FEATURES OF BRYOPHYTES Cont’d The sporophyte is unbranched and produces a single terminal sporangium The spore coat is cutinized and the spores are generally disseminated through the air The sporophyte and the gametophyte possess no lignified tissue GENERAL FEATURES OF BRYOPHYTES Cont’d The gametophyte is generally perennial It often consists of a juvenile, usually filamentous phase (PROTONEMA) and a more complex phase that actually produces the sex organs  A protonema (plural: protonemata) is a thread-like chain of cells that forms the earliest stage of development of the gametophyte (the haploid phase) in the life cycle of mosses.  When a moss first grows from a spore, it starts as a germ tube, which lengthens and branches into a filamentous complex known as a protonema, which develops into a leafy gametophore, the adult form of a gametophyte in bryophytes.  GENERAL FEATURES OF BRYOPHYTES Cont’d The male gametes (sperms) are biflagellate with whiplash flagella and must reach the egg through a film of water They are produced in the ANTHERIDIUM, that is, a stalked sac  GENERAL FEATURES OF BRYOPHYTES Cont’d This sac is composed of sterile unistratose (one cell in thickness) jacket enclosing innumerable cells, each of which produces a sperm The female sex organ (ARCHEGONIUM) is flask-shaped; ✓the neck of the flask is unistratose, while the lower expanded portion (VENTER) is multistratose  GENERAL FEATURES OF BRYOPHYTES Cont’d Each archegonium encloses a single egg Bryophytes are generally small with the sporophyte usually not more than 3cm tall and the gametophyte usually less than 10cm tall ✓although erect forms may exceed 20cm and reclining aquatic or hanging forms may reach a meter in length  CLASSIFICATION The Bryophytes fall naturally into three classes: ✓CLASS HEPATICAE (Liverworts) ✓CLASS ANTHOCEROTAE (Hornworts) ✓CLASS MUSCI (Mosses)  CLASSIFICATION Cont’d The features used in this classification are: ✓the nature of the thallus and (where present) of the leaves, ✓the extent of the development of the juvenile phase of the gametophyte (PROTONEMA) and ✓the presence or absence of an opening mechanism in the capsule  There is, however, no general agreement concerning the number of Orders among the Bryophyta  ORDER MARCHANTIALES (Thalloid Liverworts) CLASS HEPATICAE eg. Marchantia, Riccia (Liverworts) ANACROGYNOUS ORDER JUNGERMANNIALES eg. Pellia (Thalloid) ACROGYNOUS eg. Porella (Leafy) DIVISION CLASS BRYOPHYTA ORDER ANTHOCEROTALES (Only Order) ANTHOCEROTAE Gametophyte simple and thalloid but (Horned Liverworts) Sporophyte complex eg. Anthoceros ORDER SPHAGNALES (Peat/Bog mosses) CLASS MUSCI eg. Sphagnum (Mosses) ORDER ANDREAEALES (The Lantern mosses) eg. Andreaea ORDER BRYALES (True mosses) Gametophyte distinctively leafy and Sporophyte very complex eg. Funaria, Polytrichum  Acrogyny: the condition in hepatics in which the female sex organs terminate the main shoot; the apical cell produces these organs Anacrogyny: the condition in hepatics in which the female sex organs are produced by a lateral cell; thus the growth of the main shoot of the gametophyte is indeterminate, and sporophytes are lateral  CLASS HEPATICAE - THE LIVERWORTS The Hepaticae are the most primitive bryophytes The name liverwort (“liver-plant”) was probably applied to these plants because of the fancied resemblance of the thallus of some of these plants to the liver CLASS HEPATICAE - THE LIVERWORTS Cont’d ✓and the belief that plants resembling human organs would cure diseases of the organs they resembled A prescription for a liver complaint in the 1500s therefore called for “liverworts soaked in wine” Unfortunately, there is no evidence that liverworts possess curative properties CLASS HEPATICAE - THE LIVERWORTS Cont’d The hepatics possess a number of features that distinguish them from the mosses The “protonema” is usually reduced to two or three cells of the uniseriate (filament made up of a single linear series of cells) germ tube ✓and the apical cell of the gametophyte is differentiated early  The rhizoids are generally unicellular ✓ and are not branched, although the tip is sometimes knobbed The pronematal phase produces no gemmae The gametophyte is either leafy or thallose ✓ and leaves are arranged in two or three rows CLASS HEPATICAE - THE LIVERWORTS Cont’d Sex organs lack paraphyses (filamentous sterile structures intermixed among the sex organs of most mosses) among them ✓but mucilage filaments are usually present Leaves are usually unistratose ✓and lack a costa (thickened midrib of a moss leaf or hepatic thallus)  CLASS HEPATICAE - THE LIVERWORTS Cont’d Leaf cells are commonly isodiametric (of equal length and width) ✓and frequently possess trigones (3- angled structures of equal length and width) Gametophyte cells often have complex oil bodies Leaves are often lobed  The jacket of the sporangium never has stomata Cells of the sporangium jacket often have transverse or nodular thickenings The sporangium jacket is sometimes unistratose The sporangium usually opens by four longitudinal lines CLASS HEPATICAE - THE LIVERWORTS Cont’d Even in rare cases where there is an operculum, peristome teeth are absent Within the sporangium, there are often sterile threadlike hygroscopic cells with helical thickenings ✓These are ELATERS A columella is absent CLASS HEPATICAE - THE LIVERWORTS Cont’d The sporophyte usually produces a colorless seta of thin-walled cells ✓and is held rigid by turgor pressure in the component cells The sporophyte generally persists for a very brief period after the spores are shed  The calyptra is ruptured and remains at the base of the seta when the seta elongates rapidly ✓ and protects the maturing sporangium before seta elongation CLASS HEPATICAE - THE LIVERWORTS Cont’d The seta elongates after the sporangium is completely differentiated with the included spores and elaters ✓and the seta is rarely a photosynthetic organ Generally, all spores in a sporangium are shed at the same time CLASS HEPATICAE ORDER MARCHANTIALES  MARCHANTIA The best known species of thalloid liverworts are in the genus Marchantia The thallus which is about 30 cells thick in the centre and 10 cells thick at the margin, forks dichotomously as it grows Each branch has a notch at the apex and a central groove that extends back lengthwise behind the notch  MARCHANTIA Cont’d The thalli grow as meristematic cells at the notches divide Older tissues at the rear decay as new growth is added The upper surface of the thallus is divided into diamond-shaped or polygonal segments, the segment lines marking the limits of the chambers below  MARCHANTIA Cont’d Each segment has a small bordered pore opening into the interior Seen through a microscope, a sectioned liverwort thallus looks a little like a series of covered prickly pear (cactus) gardens sitting on a decorative rock wall SECTION THROUGH A PORTION OF MARCHANTIA THALLUS  MARCHANTIA Cont’d The ‘rock wall’ which may comprise most of the thallus, consists of parenchyma cells that have few, if any, chloroplasts The tissue apparently stores substances produced in other cells The bottom layer of cells is an epidermis from which rhizoids and scales arise  MARCHANTIA Cont’d The ‘cactus gardens’ consist of upright branching rows of chlorenchyma cells in an air space Vertical walls enclose the individual ‘gardens’ which are covered by a slightly dome-shaped layer of epidermal cells  MARCHANTIA Cont’d The conspicuous pore, which remains open at all times, is located in the centre of each ‘roof’ and looks something like a short, suspended, open-ended barrel The pore, like the stoma of a higher plant, allows aeration of the thallus with the minimum dehydration, but is incapable of significant change in its aperture SECTION THROUGH A PORTION OF MARCHANTIA THALLUS  ASEXUAL REPRODUCTION Marchantia reproduces asexually by means of GEMMAE (sing. GEMMA) Gemmae are tiny, lens-shaped pieces of tissue that become detached from the thallus They are produced on GEMMA CUPS scattered over the upper surface of the liverwort gametophyte LIFE CYCLE OF MARCHANTIA  Raindrops may splash the gemmae as much as 1 meter (3 feet) away While gemmae are in the cup, lunuraric acid (an endogenous growth regulator found in the liverworts) inhibits their further development, but each is capable of growing into a new thallus as soon as it is out of the cup  ASEXUAL REPRODUCTION Cont’d In addition, parts of an older thallus may die, isolating patches of active tissue, which may then continue to grow independently Marchantia is DIOECIOUS ie. the male and female plants are distinct and separate  SEXUAL REPRODUCTION The gametangia are produced on separate male and female gametophytes and are more specialized than those of other liverworts Both types of gametangia are formed on GAMETANGIOPHORES which are umbrella-like structures borne on slender stalks arising from the central grooves of the thallus  SEXUAL REPRODUCTION Cont’d The top of the male gametangiophore, termed ANTHERIDIOPHORE, is disc-like with a scalloped margin, while that of the female gametangiophore, termed ARCHEGONIOPHORE, looks like the hub and spokes of a wagon wheel  ANTHERIDIA, which are club-shaped male gametangia containing numerous sperms are produced in rows just beneath the upper surface of the antheridiophore The sperms are extruded in a mucilaginous mass  SEXUAL REPRODUCTION Cont’d ARCHEGONIA, which are flask-like female gametangia, each containing a single egg, are also produced in rows and hang neck downward beneath the spokes of the archegoniophore LIFE CYCLE OF MARCHANTIA  Raindrops sometimes splash the released sperms, which have flagella, more than 0.5 meter (1.5 feet) away Fertilization may occur before the stalks of the archegoniophores have finished growing After fertilization, the zygote develops into a multicellular EMBRYO (an immature sporophyte)  SEXUAL REPRODUCTION Cont’d Embryos are diploid, the nuclei of all cells containing 2n chromosomes A knoblike FOOT anchors the sporophyte (the diploid, spore- producing phase) in the tissues of the archegoniophore The sporophyte hangs suspended by a short, thick stalk called the SETA LONGITUDINAL SECTION THROUGH SPOROPHYTE OF MARCHANTIA  The main part of the sporophyte, in which different types of tissue develop, is called a CAPSULE/SPORANGIUM Liverwort sporophytes typically have no stomata SPORE MOTHER CELLS/SPOROCYTES in the capsule undergo meiosis, producing haploid spores  SEXUAL REPRODUCTION Cont’d Other capsule cells do not undergo meiosis but remain, diploid and develop, instead into long, pointed ELATERS, which have spiral thickenings and are sensitive to changes in humidity Spore dispersal in Marchantia takes place as the elaters twist and untwist rapidly  In the sporophytes of other liverworts, the elaters may aid spore dispersal with a snapping action or by suddenly expanding  ORDER JUNGERMANNIALES (LEAFY LIVERWORTS) This is the largest order of the liverworts containing about two-thirds of all species in the Hepaticae They are often abundant in tropical jungles and in fog belts  VEGETATIVE STRUCTURE The gametophytes of these liverworts are leafy, in contrast to thalloid plants ✓ that is, the gametophytes have stem- like and leaf-like organs (that may be held somewhat erect, off the ground) A very common widespread genus is Porella Other examples are Frullaria, Lophocolea, Marsupella  VEGETATIVE STRUCTURE Cont’d Leafy liverworts always have two rows of partially overlapping leaves whose cells contain distinctive oil bodies The leaves consist of a single layer of cells and have no midribs Unlike the leaves of mosses, they often have folds and lobes  In the tropics, the lobes form little water pockets in which tiny animals are always present It has been suggested that this water pockets may function like the pitchers of pitcher plants  VEGETATIVE STRUCTURE Cont’d A third row of underleaves (AMPHIGASTRIA) which are smaller than the other leaves and not visible from the top, is often present on the underside of leafy liverworts Classification of the leafy liverworts is based largely on the arrangement and lobing of the leaves  VEGETATIVE STRUCTURE Cont’d When the anterior margins of the leaves lie regularly beneath the posterior of those in front, the arrangement is said to be SUCCUBOUS and when the converse occurs, the arrangement is said to be INCUBOUS A few rhizoids, which anchor the plants, develop from the stem-like axis at the base of the underleaves INCUBOUS SUCCUBOUS  SEXUAL REPRODUCTION Reproduction is essentially similar to that described for the Marchantiales Specialized gametophores are however, never produced Both monoecious and dioecious forms occur, sometimes in the same genus  Archegonia are always restricted to the apices of the stem and its branches Because they are apical, they, and ultimately the sporophyte, terminate growth of the main shoot so that vegetative growth is continued by lateral, sympodial branching  SEXUAL REPRODUCTION Cont’d Archegonia are generally enclosed within a cylindrical unistratose chlorophyllose tube, the PERIANTH Sporophytes resemble those of Marchantia At maturity, the sporophyte capsule may be pushed out from among the leaves as the seta elongates  SEXUAL REPRODUCTION Cont’d The sporangium/capsule usually opens by four longitudinal lines When a spore germinates, it produces a PROTONEMA, which consists of a short filament of photosynthetic cells The protonema soon develops into a new gametophyte  PORELLA OCCURRENCE Porella is a common acrogynous, leafy liverwort Acrogynous - having the female reproductive organ arising from the apical cell of the stem, thereby terminating its growth  It grows on moist rocks, tree trunks and old walls and forms a compact greenish patch, practically covering the medium on which it grows  VEGETATIVE STRUCTURE The plant body consists of a slender, dorsiventral, prostrate stem and leafy branches The lower side of the stem bears several rhizoids, primarily for anchorage The leaves are arranged in three rows: two rows of dorsal leaves and a row of ventral, small leaves called AMPHIGASTRIA  The dorsal leaves are unequally bi- lobed and overlapping The plant grows by means of an apical tetrahedral cell, which cuts off segments on three sides  REPRODUCTION VEGETATIVE REPRODUCTION may take place by the breaking off of the branches, or by the formation of unicellular or multicellular gemmae on the margin or at the apex of the leaf  SEXUAL REPRODUCTION Porella is dioecious The male plants are usually smaller and produce special short and lateral antheridial branches These bear antheridia, each in the axil of a leaf (or bract)  SEXUAL REPRODUCTION Cont’d Paraphyses may be present Paraphyses - sterile hairlike filaments present among the reproductive organs in many lower plants Each antheridium is a globular body surrounded by a wall (jacket) and provided with a long, multicellular stalk  It is packed with antherozoid mother cells (androcytes), each giving rise to a minute biciliate antherozoid Each archegonium has a short multicellular stalk, a venter with an egg cell and an egg nucleus, a ventral canal cell, a long neck with 6-8 neck canal cells, and a wall  SEXUAL REPRODUCTION Cont’d The neck is nearly as broad as the venter Fertilization takes place in the usual way The anterozoids, when liberated, swim in water to the archegonium  They enter through the apical opening and finally, one of them fuses with the egg nucleus The fertilized egg forms a zygote  SPOROPHYTE The zygote secretes a wall round itself and soon grows in size It divides and redivides and soon gives rise to a sporophyte This consists of a foot, seta and capsule The capsule is globose and surrounded by a wall (jacket), 2 or 4 layers thick  SPOROPHYTE Cont’d It encloses short, slender, spirally thickened elaters and many spores The sporophyte is surrounded by a calyptra, perianth and involucre The calyptra is the envelope developed from the venter The other two envelopes are formed by united leaves (or bracts)  GERMINATION OF THE SPORE When mature, the capsule dehisces by four valves, and the spores are liberated Under favourable conditions, the spore germinates and gives rise to a small, multicellular body, the PROTONEMA  Soon its apical cell becomes active and produces the shoot and leaves of a new Porella plant  CLASS II CLASS ANTHOCEROTAE – THE HORNWORTS  The Class Anthocerotae contains a single order Anthocerotales Although formerly included with the Hepaticae the Anthocerotales are now placed in a separate class ✓ mainly on account of their unique sporophyte  CLASS ANTHOCEROTAE Cont’d Mature sporophytes of the Anthocerotae (hornworts) look like miniature, greenish cattle horns Anthoceros is representative of its class  STRUCTURE AND FORM The Anthocerotae have the simplest gametophyte of the Bryophytes But the sporophytes are more complicated than that of any other order The gametophytes are slightly lobed with numerous rhizoids growing from the lower surface  STRUCTURE AND FORM Cont’d They are small, green thalloid plants with little internal differentiation of vegetative tissues They are usually less than 2cm in diameter and thrive in moist soil in shaded areas although some occur on trees  Hornworts usually have one large chloroplast in each cell (a few have up to eight) Each chloroplast has pyrenoids similar to those of green algae, a feature not found in other Bryophytes The pyrenoid consists of a mass of minute disc or spindle-shaped bodies which are the rudiments of starch grains  STRUCTURE AND FORM Cont’d The thalli have pores and cavities filled with mucilage in contrast to the air-filled pores and cavities of thalloid liverworts Nitrogen-fixing blue-green bacteria/algae (e.g. Nostoc) often grow in the mucilage  The internal structure of the thallus is very simple consisting of a mass of thin- walled parenchyma cells without any differentiation of tissues  ASEXUAL REPRODUCTION Hornworts reproduce asexually primarily by fragmentation ✓or as lobes separate from the main part of the thallus A few hornworts form tiny tubers on the margin which grow into new gametophytes  SEXUAL REPRODUCTION Like both mosses and liverworts some species of hornworts are monoecious (bisexual/homothallic) bearing both antheridia and archegonia ✓while other species are dioecious (unisexual/heterothallic) bearing either of the two  SEXUAL REPRODUCTION Cont’d The antheridia are similar in structure to those encountered in the Hepaticae They grow in small groups usually 2-4 and are located in roofed chambers in the upper portion of the thallus  Each antheridium consists of ✓ a short multicellular stalk ✓a sterile outer layer (one or more cells thick) and, ✓a compact mass of antherozoid mother cells Each mother cell gives rise to a single minute biciliate antherozoid (sperm cell)  SEXUAL REPRODUCTION Cont’d The archegonia develop singly and separately and are embedded within the thallus and in direct contact with the vegetative cells surrounding them When fully developed each archegonium consists of a venter and a neck  SEXUAL REPRODUCTION Cont’d The neck consists of a vertical row of 4-6 neck canal cells The venter consists of a ventral canal cell and an egg cell  SEXUAL REPRODUCTION Cont’d At maturity the neck canal cells and the ventral canal cells get disorganized and become converted into mucilage While the major part of the archegonium remains sunken in the thallus the upper end of the neck only projects out of it  SEXUAL REPRODUCTION Cont’d When young the neck of the archegonium is covered by four cells which separate out later Fertilization By the breakdown of the roof of the antheridial chamber an outlet is formed for the antherozoids to escape  SEXUAL REPRODUCTION Cont’d They swim to the archegonium and enter through the neck Finally one antherozoid fuses with the egg nucleus in the venter A zygote is formed after fertilization  SPOROPHYTE The sporophyte develops from the zygote and consists of a FOOT and CAPSULE For a time it is surrounded at the base by a sheath or INVOLUCRE formed by an upward growth of the archegonium  Soon after fertilization the zygote grows and completely fills up the venter By repeated divisions it gives rise to ✓ the FOOT embedded in the thallus below, serving as an absorbing organ ✓and the CAPSULE above There is no seta of the capsule in Anthoceros  The capsule (sporangium) is ✓an upright ✓slender, cylindrical ✓deep green structure ✓usually 1-3cm long ✓but sometimes much longer in a few species The following regions can be seen in a longitudinal section through the capsule: ❖A MERISTEMATIC TISSUE At the base of the capsule just above the foot through the activity of which the sporophyte continues to elongate and the sporocytes (spore mother cells) continue to be formed ❖Centrally there is a sterile tissue, the COLUMELLA, consisting of rows of elongated cells The sterile columella is an early indicator of the differentiation of the conducting system at a later stage in higher plants ❖Surrounding the columella is a cylinder of SPOROGENOUS TISSUE The sporogenous tissue is surrounded by the CAPSULE WALL which is a jacket of green sterile tissue 4-8 layers of cells in thickness ✓ each cell having 2 or sometimes more chloroplasts  The outermost layer of the capsule wall is the epidermis ✓ which is strongly thickened and cutinized and provided with stomata The sporogenous tissue may extend down to the base of the capsule or only half-way down ✓ and may be 1, 2, 3 or 4 layers of cells in thickness  The sporophyte matures from the apex downwards i.e. the base is younger than the apex The sporogenous cells develop into small groups of sterile cells called ELATERS and small groups of spores in an alternative manner The elaters are mostly smooth- walled and rarely with spiral bands  Each spore mother cell undergoes reduction division and four spores are formed in a tetrad Spores mature in progression from top to down The gametophyte generation begins with the formation of the spores  When the spores at the top of the capsule are ripe the tip of the sporophyte horn splits into two or three ribbon-like segments releasing the spores And the segments continue to peel back as long as the meristem is producing new tissue at the base with the slender columella standing free in the center  Because of the presence of chloroplasts the sporophyte can manufacture most of its food and is dependent on the gametophyte only for water and mineral salts The sporophyte is therefore a semi-independent body  Under exceptionally favourable growing conditions the sporophyte may lengthen greatly Some sporogenous tissue at the base of the capsule may be replaced by a conspicuous conducting strand The foot enlarges and through decay of gametophyte comes into more or less direct contact with the soil  Such sporophytes are capable of maintaining themselves independently for some time And they represent the most primitive sporophytic terrestrial plants  DEVELOPMENT OF ANTHOCEROTAE SPOROPHYTE TOWARDS INDEPENDENT LIFE i. The development of a considerable amount of green tissue and stomata ii. Development of massive foot to facilitate greater absorption of water and mineral salts from the gametophyte  With the decay of the gametophyte tissue the foot may even touch the ground and absorb water and mineral salts from the soil iii. The complexity of the sporophyte with a considerable development of sterile tissue is an early indication of a more complex and quite independent sporophyte at a later stage in the evolution of higher plants iv. The development of the sterile axis (columella) represents the beginning of a conducting system v. The method of shedding spores can be compared to that of ferns and allied plants  CLASS III MUSCI – THE MOSSES ORDER I: ORDER SPHAGNALES – PEAT MOSSES/BOG MOSSES  ORDER I: ORDER SPHAGNALES – PEAT MOSSES/BOG MOSSES The Sphagnales, represented by a single genus, Sphagnum are confined to acid waterlogged habitats They are the principal components of peat bogs where they form a more or less continuous layer  Peat bog is a type of wetland whose soft, spongy ground is composed largely of living and decaying Sphagnum moss. Decayed, compacted moss is known as peat, which can be harvested and used for fuel or as a soil additive.  Sphagnum has a special capacity for retaining water in its body It is therefore extensively used as good stuffing material for pot herbs and hanging plants like orchids to keep them moist  Being soft and antiseptic it makes a good surgical dressing material It forms peat which may be used as fuel It is also added to alkaline soils to neutralize them  GAMETOPHYTE The gametophyte consists of ✓ a long or short slender erect axis usually a few centimeters on land and sometimes about two meters in water ✓a profusion of slender branches ✓a dense mass of minute greenish leaves ✓and sex organs on special short branches near the apex  GAMETOPHYTE Cont’d The plant is perennial in habit ✓and continues to grow almost indefinitely by a tetrahedral apical cell The older parts always die off from below The leaf is ovate and linear, composed of a single layer of cells ✓and has no mid-rib  GAMETOPHYTE Cont’d Under the microscope the leaf is seen to be composed of ✓a network of elongated narrow green cells containing chloroplasts ✓interspersed with large broad hyaline dead cells filled with water Such cells are spongy, absorbing and retaining water in enormous quantities  B A A: Adaxial surface showing arrangement of cells of leaf B: Transverse section of leaf  GAMETOPHYTE Cont’d The big mass of dead parts accumulating year after year forms peat which in the course of time may cover up a bog or even a lake The acid water in which the plant grows discourages bacterial activity and retards the decay of dead parts  ANATOMY OF STEM Internally the stem is differentiated into three distinct regions: ✓a central pith or medulla made of thin- walled colourless cells ✓a narrow cylinder of thick-walled cells acting as a supporting tissues: ✓ the cell walls of this tissue may be of various colours - red, brown, yellow, blackish or greenish, and ✓externally a spongy cortex consisting of one layer (varying, however from 1 to 5 according to species) of dead hyaline cells with circular or oval pores on their walls and sometimes spiral thickening  These features are not however constant The cortex absorbs and retains water  SEXUAL REPRODUCTION Sphagnum may be monoecious, bearing both the antheridia and archegonia on the same plant ✓or dioecious, bearing the sex organs on separate plants  The antheridia are borne singly, ✓each in the axil of a coloured leaf (reddish, purplish or brownish on special short, stout, lateral branches (antheridial branches) near the apex of the shoot  SEXUAL REPRODUCTION Cont’d Each antheridium is ovoid or spherical and has a slender long stalk It consists of a mass of antherozoid mother cells (androcytes), each giving rise to biciliate antherozoids The two cilia are of equal length Longitudinal section through sporogonium/ mature sporangium/capsule  SEXUAL REPRODUCTION Cont’d The archegonia grow in a group of three (varying, however from 1 to 5) at the apex of very short branches (archegonial branches) just below the apex of the axis  Each archegonium consists of ✓a swollen venter with an egg ✓a long neck with canal cells surrounded by a wall ✓and has a long multicellular stalk  FERTILIZATION The antheridium bursts irregularly at the apex into valves and antherozoids are liberated They swim to the mature archegonium and enter it though the open neck (neck canal cells dissolve into mucilage)  FERTILIZATION Cont’d One of the antherozoids then fuses with the egg-nucleus The zygote formed divides repeatedly and finally a spherical or ovoid spore- bearing body, the SPOROGONIUM is formed on top of the branch Usually only one zygote of an archegonial branch develops into a sporogonium  SPOROPHYTE The sporogonium is the sporophyte reproducing asexually by means of spores It consists of ✓a CAPSULE (SPORANGIUM) developing from the upper part of the filament ✓a very short neck-like stalk called the SETA (often remaining undeveloped) ✓a large bulbous FOOT developing from the lower part of the filament ✓and a PSEUDOPODIUM  SPOROPHYTE Cont’d ▪ The sporogonium in longitudinal section shows the following regions: There is a compact mass of colourless sterile cells forming the COLUMELLA at the centre A dome-shaped SPORE SAC containing numerous spores formed in tetrads occurs on top of the columella Longitudinal section through sporogonium/ mature sporangium/capsule  SPOROPHYTE Cont’d There is a lid or cover known as the OPERCULUM on top of the capsule; ✓The Operculum has a ring-like layer of thickened cells known as ANNULUS The capsule wall is made of a layer of thick-walled, cutinized cells internal to it, ie. the EPIDERMIS, and a few layers of thin-walled cells internal to it, the SUB-EPIDERMIS  SPOROPHYTE Cont’d Rudimentary (not yet fully developed) stomata (two guard cells only, without any chloroplasts or opening) are present in the epidermis  SPOROPHYTE Cont’d The capsule, however, is greenish in colour containing some chloroplasts The whole capsule is bound by a loose cap or CALYPTRA which is the enlarged and stretched archegonium wall Soon however it is torn off  SPOROPHYTE Cont’d The seta is very short (almost absent), ✓and the function of elevating the capsule is taken over by a false stalk or PSEUDOPODIUM (base of the female inflorescence) ✓which develops from the stem at the base of the capsule  As the spores begin to mature the stalk elongates rapidly and pushes up the capsule When the capsule is ripe the columella shrinks away from the spore-sac leaving an air-cavity in between  SPOROPHYTE Cont’d The spore-sac now assumes a cylindrical form The compressed air contained in the air-space exerts a heavy pressure on the spore-sac with the result that the capsule explodes, blowing off the lid and scattering the spores Longitudinal section through sporogonium/ mature sporangium/capsule  GERMINATION OF SPORE The spores germinate to form a filament but this is rapidly replaced by a small thalloid protonema This in turn gives rise to a bud which develops into the familiar leafy gametophyte, the protonema meanwhile becoming moribund (near to end of existence) and disappearing  VEGETATIVE PROPAGATION This is very common in Sphagnum, helping the plant to multiply rapidly and spread over large areas The methods are: ✓Separation of some of the long and strong branches after the death of the older parts  VEGETATIVE PROPAGATION Cont’d ✓Development of secondary protonema by some of the short apical branches ✓Splitting of the protonema, and ✓Formation of secondary protonema from the primary protonema  ORDER II: ORDER ANDREAEALES LANTERN MOSSES - The sporangium resembles a Chinese Lantern ROCK MOSSES - Grow on bare exposed rocks  ORDER ANDREAEALES The Andreaeales are another order containing only a single genus distinguished only by its peculiar capsule The leafy gametophyte of Andreaea rarely exceeds 1cm in height  It is usually found growing on rock, chiefly in cold, exposed and relatively dry regions The leaves are olive-brown in colour, composed of rounded cells, and in most species showing no distinct mid-rib  ORDER ANDREAEALES Cont’d Sex organs are formed apically The sporophyte resembles that of Sphagnum in having a domed sporogenous layer (archesporium) and being borne on a pseudopodium at maturity Dehiscence of the capsule takes place by four longitudinal slits which do not meet at the tip  ORDER ANDREAEALES Cont’d The hygroscopic properties of the wall cause the slits to close in damp conditions and to open again in dry conditions The protonema of Andreaea is similar to that of Sphagnum ORDER III: ORDER BRYALES – TRUE MOSSES  ORDER III: ORDER BRYALES – TRUE MOSSES Mosses occur most commonly on old damp walls, trunks of trees and damp soil, during the rainy season and dry up in the dry season They are gregarious in habit; wherever they grow they form a green patch or soft, velvet-like green carpet  Common examples are Mnium, Funaria and Polytrichum Some species eg. Tortula ruraliformis are able to survive periods of drought in sand dunes and other arid habitats  The cells of these species appear to have acquired the capacity to continue metabolism at a reduced rate while partially dehydrated At the other extreme are a few sub- aquatic species such as Fontinalis autipyretica  Some mosses are remarkably tolerant of heavy metals and in some areas serve as indicator plants (Heavy metal: Any metal with a specific gravity of 5.0 or greater, especially one that is toxic to organisms eg. lead, mercury, copper, and cadmium)  The worldwide genus Mielichhoferia for example, contains a number of species characteristic of acidic copper- bearing soils and rocks  GAMETOPHYTE The moss plant is small, usually a few centimeters in height and consists of a short axis with spirally arranged minute green leaves The axis may be branched or unbranched The mature stem of the leafy gametophyte shows a wide range of differentiation depending on the species, age and environment  GAMETOPHYTE Cont’d Enlarged cells called RHIZOIDS anchor the gametophyte to the substrate These structures are not roots and apparently not involved in absorption (of water and mineral salts)  The stems of simpler mosses like Tetraphis have an outer layer of thick- walled epidermal cells (STEREIDS) surrounding an undifferentiated cortex made up of parenchyma-like cells Some mosses, such as Mnium have a central conducting strand in their stems  GAMETOPHYTE Cont’d The stem of Mnium is made up of elongated thin-walled HYDROIDS which are dead empty cells that conduct water Their end walls are oblique and sometimes very thin, perforated with pores or partly dissolved  GAMETOPHYTE Cont’d The mid-rib of some mosses’ leaves also contain hydroids but only in one genus is this known to connect with the hydroids of the stem Hydroids show some resemblance to tracheids but lack specialized pitting and lignified walls No lignin has been detected in Bryophytes  GAMETOPHYTE Cont’d A few of the most specialized mosses also contain cells resembling the sieve cells of the vascular plants Between the epidermis and the central strand elongated cells with oblique end walls (LEPTOIDS) may occur These cells are alive, but their nuclei are degenerate and inactive  GAMETOPHYTE Cont’d They have many enlarged plasmodesmata in their end walls 35 - 40nm in diameter and callose may be present Studies with 14CO2 show that sugars may be translocated through these cells at the rates of 0.3-50cm/hr  Although leptoids are always associated with parenchyma cells it is not yet clear if the parenchyma cells function as companion cells The leaves of moss gametophytes have no mesophyll tissue, stomata or veins like the leaves of more complex plants  GAMETOPHYTE Cont’d The blades are nearly always mainly one cell thick except at the MIDRIB, which runs lengthwise down the middle, and they are never lobed nor divided, nor do they have a petiole The midrib (often referred to as a NERVE), which is absent in some genera sometimes projects beyond the tip in the form of hair or spine  GAMETOPHYTE Cont’d The leaf cells usually contain numerous lens-shaped chloroplasts, except at the midrib The most complex leaf is found in Polytrichum and its allies Here a number of parallel longitudinal lamellae grow up from the upper surface and chloroplasts occur principally in these cells  REPRODUCTION ASEXUAL REPRODUCTION Vegetative propagation plays a large part in the reproduction of the Bryales Almost any part of the gametophyte – leaf, stem or even rhizoid - is capable of regeneration, either directly or by the production of gemmae and giving rise to a new individual  SEXUAL REPRODUCTION Sexual reproduction begins with the formation of multicellular gametangia, usually at the apices of leafy shoots of gametophytes although they frequently form on special separate branches Both male and female gametangia are often produced on the same plant but in some species they occur on separate plants  SEXUAL REPRODUCTION Cont’d In Mnium, shoots bearing antheridia are easily recognized by the surrounding leaves that spread around them somewhat like petals of a flower The group of antheridia appears as an orange spot in the centre of the terminal cluster of leaves  SEXUAL REPRODUCTION Cont’d The ARCHEGONIA are somewhat cylindrical and project upward from the base of the expanded gametophyte tip When certain cells breakdown in the VENTER a cavity develops in which a single egg cell is produced The part of the archegonium above the venter is called the NECK Life cycle of a moss  SEXUAL REPRODUCTION Cont’d The neck which may taper toward the tip contains a narrow canal The canal is at first plugged with cells but these break down as the archegonium matures leaving an opening at the top Several archegonia are usually produced at the same time, with sterile hair-like, multicellular filaments called PARAPHYSES (Sing: Paraphysis) scattered among them  SEXUAL REPRODUCTION Cont’d Male gametangia also have paraphyses among them and are sausage shaped to roundish with walls that are one cell thick The antheridia are borne on short stalks A mass of tissue inside the antheridium develops into numerous coiled or comma- shaped sperm cells  SEXUAL REPRODUCTION Cont’d This mass of sperms is forced out of the top of the antheridium when it absorbs water and swells After release the sperm mass breaks up into individual cells each with a pair of flagella  It is believed the break up of the sperm mass is aided in some cases by fats produced by the moss while in other instances rain splash is responsible Life cycle of a moss  SEXUAL REPRODUCTION Cont’d And eventually a sperm cell after swimming down the neck of the archegonium unites with the egg forming a diploid zygote Archegonia release sugars, proteins, acids or other substances that attract the sperm cells  SEXUAL REPRODUCTION Cont’d The zygote usually grows rapidly into a spindle-shaped embryo The embryo breaks down the cells at the base of the archegonium and becomes firmly established in the tissues of the stem by means of a swollen knob called a foot  SEXUAL REPRODUCTION Cont’d As the embryo grows cells around the venter divide thereby accommodating its increasing size The length of the embryo soon exceeds the length of the cavity in the venter The top of the venter is split off and is left sitting like a pixie cap on top of the embryo  By this time the embryo is a developing sporophyte The pixie cap, called the calyptra, remains until the sporophyte is mature  SEXUAL REPRODUCTION Cont’d The cells of the sporophyte become photosynthetic as it develops, remaining so until maturity The sporophyte however depends to varying degrees on the gametophyte for some of its carbohydrate needs as well as for at least a part of its water and mineral salts which are absorbed through the foot  SEXUAL REPRODUCTION Cont’d The mature sporophyte is at first green and photosynthetic It consists of a capsule located at the tip of a slender stalk called the seta Depending on the species the seta may be less than 1 millimeter (0.04 inch) long Or it may be up to 15 centimeters (6 inches) long  SEXUAL REPRODUCTION Cont’d Most however are less than 5 centimeters (2 inches) long The free end of the capsule is usually protected by a little rimmed lid called the operculum which falls off at maturity  As the capsule matures sporocytes/spore mother cells inside it undergo meiosis producing haploid spores The spores often numbering in millions are released from the capsule usually through a structure called a peristome after the operculum falls off  SEXUAL REPRODUCTION Cont’d Most peristomes consist of a circular row or two of narrowly triangular and membranous teeth arranged around the rim of the capsule, each row having 16 teeth In a few species of mosses the peristome is a cone-shaped structure with pores through which the spores are released  SEXUAL REPRODUCTION Cont’d They open or close in response to changes in humidity Some rock mosses have neither a peristome nor an operculum The spores in these mosses are released when the capsule splits lengthwise along four lines  SEXUAL REPRODUCTION Cont’d In the dung mosses a putrid odour is given off when the spores are ready for release Some of the spores adhere to the legs and bodies of flies which are attracted by the odour and are disseminated as the insects clean themselves  SEXUAL REPRODUCTION Cont’d Most moss spores are however simply blown away by the wind And if they fall in a suitable damp location they usually germinate relatively quickly  HUMAN AND ECOLOGICAL RELEVANCE OF BRYOPHYTES  The bryophytes are the simplest terrestrial plants, although in some parts of the world such as the bogs of temperate regions and some forests of tropical mountains they are a dominant part of the vegetation  The dead stems and leaves accumulating below the growing surface become consolidated to peat, often many feet in depth  Extensive peat deposits have been formed from the remains of peat mosses that flourished in past eras Peat, like the undecomposed peat mosses, is used around the world as soil conditioners and as fuel  Peat has been cut into blocks, dried and burned as fuel, and in granulated form it is widely used in horticulture/agriculture as a source of humus Sphagnum makes much of the peat which is the fuel of Ireland and northwestern Europe But the moss peat of Iowa in the US is Drepanocladus  In the manufacture of Scotch whisky sprouted barley is dried on a screen over a peat fire The peat smoke permeates the barley and impacts a smoky flavour to the beverage Some bryophytes (and lichens) are pioneers on bare ro