Plant Kingdom Classification

• Whittaker classified living organisms into five kingdoms based on cell structure complexity, body complexity (unicellular/multicellular), and nutrition mode (autotrophs/heterotrophs).

Plant Kingdom Classification

• Plant classification systems from Aristotle to the 20th century fall into three categories.
• Artificial systems are based on a few morphological traits and were used by Theophrastus, Pliny, and Linnaeus.
• Natural systems consider all crucial related traits, both external and internal; Bentham, Hooker, Adanson, and Candolle used these.
• Phylogenetic systems are rooted in plants' evolutionary relationships; Eichler, Blessy, Whittaker, Engler, Prantl, and Hutchinson used phylogeny.
• Numerical taxonomy uses statistical methods and computers, giving equal weight to all traits.
• Cytotaxonomy classifies based on cell structure, like chromosome number, shape, and behavior.
• Chemotaxonomy uses plants' chemical constituents such as protein nature, DNA sequence, taste, and smell.

Eichler's Classification

• This system classifies the Plant Kingdom based on flowering.
• Plants are divided into Cryptogamae (non-flowering, seedless) and Phanerogamae (flowering, seed-bearing).
• Cryptogamae are further divided into Thallophyta, Bryophyta, and Pteridophyta based on plant body structure.
• Thallophyta plants have a thallus-like, undifferentiated plant body.
• Bryophyta plants have root-like and stem-like structures but lack vascular tissues.
• Pteridophyta plants have differentiated bodies with true roots, stems, and leaves, with vascular tissues present.
• Vascular cryptogams is another name for pteridophyta, because they have vascular tissue.
• Thallophytes are divided into Algae (pigmented), Fungi (non-pigmented), and Lichens (symbiotic algae-fungi associations).
• Phanerogamae are divided into Gymnosperms (naked seed plants) and Angiosperms (covered seed plants).
• Angiosperms are further divided into Monocots (single cotyledon, fibrous roots, parallel venation) and Dicots (two cotyledons, taproot, reticulate venation).
• Tracheophytes include Pteridophytes, Gymnosperms, and Angiosperms due to the presence of vascular tissue.
• Embryophyta includes Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms because they possess an embryo.

Algae

• Phycology is the branch of biology studying algae.
• Phycos means seaweed and logos means study.
• Fritsch is known as the Father of Phycology, and M.O.P. Iyengar as the father of Indian phycology.
• Algae are pigmented thallophytes.

Algae Habitats

• Hydrophytes live in water, xerophytes in deserts, and mesophytes in moderate environments.
• Epiphytes grow on plants, lithophytes on rocks, and halophytes in salty areas.
• Aquatic habitats include freshwater (Spirogyra) and marine (Sargassum).
• Floating algae include Chlamydomonas and Spirogyra.
• Benthophytes like Chara attach to the bottom.
• Epiphytes like Cladophora grow on plant bodies.
• Epizoic algae like Trichophillus grow on animal bodies.
• Terrestrial algae like Fritschiella grow in moist soil.

Algae Plant Body

• The vegetative plant body is a haploid gametophyte.
• Algae can be unicellular, flagellated (Chlamydomonas) or non-flagellated (Chlorella).
• Multicellular forms include coenobium (Volvox), aggregation (Tetraspora), filamentous unbranched (Ulothrix), filamentous branched (Cladophora), Siphonous (Vaucheria), and Parenchymatous (Ulva).
• Some algae have bodies like higher plants (Sargassum, Chara).

Algae Nutrition and Pigments

• Most algae are autotrophs, performing photosynthesis, while some are parasitic (Cephaleuros).
• Algal pigments include chlorophylls (a, b, c, d), carotenoids (carotene, xanthophyll, fucoxanthin), and phycobilins (phycocyanin, phycoerythrin).

Algae Reproduction

• Algae reproduce vegetatively via fragmentation, budding, tubers, or gemmae.
• Asexual reproduction occurs without gamete fusion, mainly through zoospores, aplanospores, akinetes, hypnospores, endospores, exospores, or auxospores.
• Palmella stage occurs when spores become colonial (Ulothrix, Chlamydomonas).
• Sexual reproduction involves similar (homogametes) or dissimilar (heterogametes) gametes and includes isogamy, anisogamy and oogamy.
• Isogamy is the fusion of morphologically and physiologically similar gametes and can be flagellated (Chlamydomonas) or nonflagellated (Spirogyra).
• Anisogamy is the fusion of morphologically or physiologically dissimilar gametes (Chlamydomonas, Spirogyra).
• Oogamy is the fusion of morphologically and physiologically dissimilar gametes (Fucus, Volvox).
• Some algae have unicellular antheridium and oogonium (Oedogonium).
• Special reproductive structures include conceptacles (Sargassum) and globule/nucule (Chara).
• Spirogyra exhibits conjugation, a special type of sexual reproduction.
• Algal life cycles alternate between haploid and diploid phases.

Algae Classification

• Algae are classified into Chlorophyceae, Phaeophyceae, and Rhodophyceae.

Chlorophyceae

• The plant body can be unicellular (Chlamydomonas), colonial (Volvox), or filamentous (Spirogyra).
• Chloroplasts have various shapes, including ribbon-like and spiral (Spirogyra), girdle-shaped (Ulothrix), cup-shaped (Chlamydomonas), star-shaped (Zygnema), disc-shaped (Caulerpa), and reticulate (Oedogonium).
• Photosynthetic pigments are chlorophyll a and b.
• Food is stored as starch or oil droplets.
• Pyrenoids, storage bodies, are present.
• The cell wall consists of cellulose and an outer layer of pectose.
• Reproduction occurs vegetatively by fragmentation, asexually by flagellated zoospores, and sexually by isogamy, anisogamy, or oogamy.
• Common members include Chlamydomonas, Chlorella, Volvox, Ulothrix, Ulva, Caulrepa, Chara, and Acetabularia.

Phaeophyceae

• These are marine algae.
• They range from simple, branched, and filamentous (Ectocarpus) to flat, ribbon-shaped (Sargassum, Laminaria, Fucus).
• Kelps are giant brown algae and the largest sea plants, exist freely as epiphytes (Ectocarpus), or free-floating (Sargassum).
• The plant body’s three parts are the holdfast (fixing structure), stipe (stalk), and frond (leaf-like structure).
• Pigments are chlorophyll a, c, carotenoids, and xanthophylls.
• Food is stored as laminarin and mannitol.
• Cell walls are made of cellulose and algin, preventing drying in low tide.
• Cells have organelles and a central vacuole for buoyancy.
• Vegetative reproduction occurs via fragmentation.
• Asexual reproduction happens through biflagellated, pear-shaped zoospores.
• Sexual reproduction involves isogamy, anisogamy, or oogamy via pear-shaped gametes with two lateral flagella.
• Common species include Ectocarpus, Laminaria, Dictyota, Sargassum, and Fucus.

Rhodophyceae

• This is commonly called red algae.

• Mostly marine, rarely freshwater.

• Example: Batrachospermum.

• They are found in well-lit regions and deep in the ocean.

• The thallus is multicellular.

• Pigments include chlorophyll a, d, and phycoerythrin, with r-phycoerythrin giving them their red color.

• Food is stored as floridean starch.

• Vegetative reproduction happens by fragmentation.

• Asexual reproduction is through non-motile spores.

• Sexual reproduction Involves Oogamy.

• Common species include Polysiphonia, Porphyra, Gracilaria, Gelidium, and Betrachospermum.

Economic Importance of Algae

• Algae are primary food chain producers in aquatic ecosystems.
• They contribute to 50% of the total carbon dioxide fixation on Earth through photosynthesis.
• They help purify air and water.
• Some algae are edible (Chlorella, Spirulina, Laminaria, Porphyra, Sargassum, Ulva), some are used as fodder (Laminaria, Sargassum, Fucus).
• Algae, such as Chlorella and Spirulina, are food supplements for space travelers.
• Hydrocolloids like algin and carrageenan are derived from red algae.
• Agar, from Gelidium and Gracilaria, is used to grow microorganisms.
• Algae are used to make culture media to do tissue culture experiments.
• Algae are used to make medicinal antibiotics (Chlorella, Polysiphonia).
• Algae are sources of minerals (Polysiphonia, Laminaria).
• Algae are used for biological research (Chlorella, Acetabularia).

Common Names of Algae

• Spirogyra is also known as water silk.
• Ulva is also known as sea lettuce.
• Acetabularia is also known as umbrella plant.

Bryophytes

• Bryophytes are the simplest non-vascular land plants with undifferentiated plant bodies.
• Bryology is the study of Bryophyta.
• Hedwig is Father of Bryology, and S.R. Kashyap is Father of Indian Bryology.
• Bryophytes are known as the amphibians of the plant kingdom.
• Bryophytes grows in dense patches on the moist shady places like walls, damp soil, tree trunks etc.

Bryophytes Features

• Bryophytes are mainly terrestrial.
• Some are aquatic, such as Riccia fluitans, and some are epiphyllous, such as Radula.
• The plant body is thallus-like and prostrate (Riccia, Anthoceros, Marchantia) or erect (Moss).
• Rhizoids, serve as root-like structures that anchor them to the soil.
• The plant body is differentiated into stem-like and leaf-like structures.
• Vascular tissues are absent.
• Vegetative reproduction occurs by fragmentation, budding, tubers, etc.
• Asexual reproduction occurs by Gemmae (asexual buds in liverworts).
• Sexual reproduction takes place in the gametophyte and are homosporous.
• Multicellular sex organs are present in clusters.
• Male reproductive organs are club-shaped antheridia, and female parts are flask-shaped archegonia.
• Antheridia produce motile, biflagellated antherozoids while archegonia produce eggs.
• Antherozoids fuse with eggs to form zygotes.
• Sporophytes are not free-living and derive nourishment from photosynthetic gametophytes.
• Haploid spores are formed in the sporophyte after meiosis, and spores germinate to form gametophytes.
• Alternation of generations occurs; haploid phases alternate with diploid phases.
• Both phases are multicellular.
• Gametophytes are the dominant photosynthetic free-living stage.
• Sporophytes are short-lived and dependent on gametophytes.
• Water is essential for fertilization.

Classification of Bryophytes

• Liverworts (Hapticospida), Hornworts (Anthocerotopsida), and Mosses (Bryopsida).

Hepaticopsida

• Liverworts have a photosynthetic, flat, dorsiventral thallus (Riccia, Marchantia).
• Rhizoids help the thallus attach to the soil.
• Vegetative reproduction is by fragmentation (Riccia, Marchantia) or gemmae formation (Marchantia).
• Gemmae are green multicellular asexual buds that develop into gemma cups, detach, and germinate to form new thalli.
• Sexual reproduction: Antheridia and archegonia form on the same or different thalli.

Anthoceropsida

• Also known as Hornworts (Anthoceros, Notothylas).
• They contain pyrenoids.
• They exhibit symbiotic nitrogen fixation.

Bryopsida

• Mosses are higher bryophytes consisting of two stages: protonema and leafy stage.
• Protonema are green, filamentous, branched, creeping structures developed from spores and bear rhizoids and lateral buds.
• Leafy developmental stages come from the secondary protonema as a lateral bud.
• Plant bodies consist of root-like, stem-like, and leaf-like structures (Funaria).
• Rhizoids are multicellular and branched, and leafy stages bear sex organs.
• Vegetative reproduction occurs by fragmentation and budding in the secondary protonema.
• Spore dispersal mechanisms are elaborate in mosses (Funaria, Polytrichum, Sphagnum).

Economic importance of Bryophytes

• They are food for herbaceous animals.
• Sphagnum Moss is used as peat fuel.
• Sphagnum Moss is used to transport of living material because of its water holding capacity
• Prevents soil erosion.
• Colonize barren rocks alongside lichens.
• Decompose rocks to create higher plant growth substrate.

Pteridophytes

• They are vascular cryptogams.
• The first terrestrial plants with xylem and phloem.
• Commonly known as botanical snakes.
• Plant bodies are differentiated into true roots, stems, and leaves.
• Sporophytic plant body.
• Stems are rhizomatous and regenerate after aerial parts are destroyed.
• Leaves can be small (microphyll) as in Selaginella or large (macrophyll) as in ferns.
• Young leaves exhibits circinate vernation (coiling of young leaves).
• Leaves are vegetative or fertile (spore-bearing sporophylls).
• Spores form inside the sporangia.
• Spore mother cells in sporangia undergo meiosis to produce spores.
• Spores germinate to form photosynthetic prothalli, bearing antheridia and archegonia.
• Prothalli require cool, damp, shady areas with water for fertilization.
• Antheridia bear antherozoids, and archegonia bear egg cell.
• Zygotes form from the sperm cell and egg cell fusion forming sporophyte.
• Most pteridophytes are homosporous, produce similar spores.
• Selaginella and Salvinia are heterosporous.
• Heterosporous plants possess microspores and macrospores germinate accordingly, becoming male and female gametophytes, respectively.
• In heterosporous conditions, female gametophytes are retained in the parent sporophyte until embryo development begins.
• Seed-bearing plants evolved from heterosporous pteridophytes.

Classification of Pteridophytes

• Psilopsida (Psilotum), Lycopsida (Selaginella), Sphenopsida (Equisetum), and Pteropsida (Pteris).

Pteridophytes Economic Importance

• Some are medicinal (Dryopteris), help in soil binding, are ornamental, edible (Marcelia), used in crop rotation (Azolla), and help with symbiotic nitrogen fixation and plays an important role in plant succession
• Creeping pine/club moss- Lycopodium
• Spike moss- Selaginella
• Water fern- Azolla
• Walking fern- Adiantum
• Adder's tongue fern- Ophioglossum
• Horse tail- Equisetum

Gymnosperms

• Have naked seeds because ovules are not enclosed in an ovary.
• They are flowerless seed-bearing plants, because Ovules are not enclosed by ovary walls.
• They were the dominant plants during the Jurassic period, and consist of medium-sized trees, tall tress and shrubs.
• Gymnosperms possess tap root systems which associate symbiotically with mycorrhiza fungi.
• Coralloid roots in Cycas contain nitrogen-fixing bacteria.
• Stems can be branched (Pinus) or unbranched (Cycas).
• Leaves adapt to extreme conditions with needle-like shapes, thick cuticles, and sunken stomata (Pinus).
• Leaves can be simple or compound.
• Vascular systems are well-developed with xylem without vessels.
• Sporophylls aggregate into strobili or cones, which exist in male and female forms.
• Male ones are short-lived while female long-lived.
• Male strobili bear microsporophylls bearing microsporangia and microspores, developing into pollen grains.
• Female strobili bear megasporophylls and megasporangia, containing megaspores.
• One megaspore becomes a female gametophyte with archegonia and pollen grains, carried by wind, reaching ovules.
• Pollen tubes reach archegonia, releasing male gametes.
• Gamete fusion produces embryos and ovules develop into seeds.
• Endosperm in gymnosperms is a pre-fertilization product and haploid.
• Photosynthetic stage is sporophyte.
• Gametophytes exist in a reduced form and not free-living.
• Classified into Cycadopsida (Cycas), Coniferopsida (Pinus), Gnetopsida (Gnetum), and Gingopsida (Ginko).

Gymnosperms Economic Importance

• Used as timber for furniture, pulp wood, pencil boxes, and musical instruments.
• Production of resins and turpentine (Pinus).
• The seeds of Cycas, Pinus, and Ginkgo are edible.
• Ephedrine is derived from Ephedra, and used for respiratory relief.
• Taxol from Taxus to freeze cancer cells
• Ginkgo is also known as Maiden hair tree.
• Cycas is also known as sago palm.

Angiosperms

• Angiosperms are flowering plants with covered seeds.
• Angiosperms are divided into Dicotyledons (two cotyledons) and Monocotyledons (one cotyledon).
• The smallest angiosperm is Wolfia.
• The large tree is Eucalyptus, which is over 100 meters.
• Reproductive organs are developed in flowers.

Angiosperms Reproductive System

• Male sex flowers possess organs called stamens with filament and anther. Anthers produce pollen grains.
• Female reproductive part is gynoecium with stigma, style and ovary.
• The ovary has one or many ovules with female gametophytes.
• Embryo sacs have seven cells and eight nuclei including an egg cell, two synergids, three antipodal cells, and one central cell having two polar nuclei.
• Pollen grains are carried by wind, water, birds, etc. and reach the stigma.
• Pollen tubes grow into the embryo sac, containing two male gametes.
• One male gamete fertilizes the egg cell syngamy, which is formed through a zygote, which later develops into an embryo.
• The other male gamete merges with secondary nuclei triple fusion to form triploid primary endosperm nucleus PEN, where PEN develops into the tissues.
• Ovules develop into seeds and ovaries into fruits.

Angiosperms Double Fertilization

• Two fertilizations occur through syngamy and triple fusion, called double fertilization.
• Endosperm is triploid.

Angiosperms Alteration of Generation

• Haplontic life cycle is the first reproductive stage: The dominant photosynthetic, free living gametophyte is produced by haploid spores. The gametophyte produces gametes by mitosis and the gametes fuse to form zygotes to represent the sporophytic stage. Zygotes undergo meiosis from haploid spores. The gametophytic phase is the most apparent at this stage. For example, Chlamydomonas.
• Diplontic life cycle: Here the diploid sporophyte is the dominant photosynthetic independent phase of the plant. The gametophytic phase is the least present shown in few gametophyte structure. The sporophytic phase is dominant. For example, angiosperms and gymnosperms.
• Haplo-diplontic life cycle: Haploid and diploid stages both go go through multicellular stages. This is seen in bryophytes and pteridophytes.