Angiosperms II Lecture Notes

Lecture 10 Angiosperms II Reproductive features II Lecture Outline Flowers – diversity (variations) primitive v. advanced Inflorescences – very brief Fruits – classification Seeds – structure of two main types patterns of germination Parts of a ‘typical’ flower 1) Calyx: Outermost layer or whorl: se...

Lecture 10 Angiosperms II Reproductive features II Lecture Outline Flowers – diversity (variations) primitive v. advanced Inflorescences – very brief Fruits – classification Seeds – structure of two main types patterns of germination Parts of a ‘typical’ flower 1) Calyx: Outermost layer or whorl: sepals Protective function Green Encircle & protect the immature flower Later open to expose the mature flower 2) Corolla: petals Attract pollinators Many forms 3) ANDROECIUM: STAMENS male reproductive whorl stamen comprised of filament anther anther (microsporophyll) bears pollen sacs (microsporangia), usually four, containing microspore mother cells (microsporocytes, 2n) producing pollen grains (microspores, n) may be in two whorls 4) GYNOECIUM (Pistil): CARPELS The female reproductive whorl carpel(s) megasporophyll(s) (often fused together) – contains the ovule(s) (megasporangium developing into megagametophyte) Diversity of flowers: modifications/variations of structure 1. number of whorls: a. if both ♀ + ♂ = bisexual/hermaphrodite (perfect flower) b. if only ♀ or ♂ = unisexual (imperfect flower) i. monoecious (e.g. corn, breadfruit) or ii. dioecious (e.g. pimento) 2. numbers of parts per whorl 3. fusion of parts 4. planes of symmetry Diversity of flowers: modifications/variations of structure 5. usually related to methods of pollination &/or seed dispersal 6. often complex! (Also: position of insertion relative to ovary; degree to which the petals overlap in bud/immature flower) 2. Number of parts per whorl Flower structure cont’d Eudicots: – Flower parts in sets of 5, sometimes 4 Monocots: – Flower parts in sets or multiples of three sepals & petals may be similar: called tepals Flower structure cont’d 3. Fusion of flower parts between members of same whorl (for most of their length): – FUSED = sym/syn- (or gamo-) – e.g. sympetalous, gamosepalous – FREE or SEPARATE members = apo- (or poly-) – e.g. apopetalous, polysepalous between members of neighbouring whorls: often stamens and petals fused: stamens said to be epipetalous (e.g. Hibiscus) Flower structure cont’d 4. Planes of Symmetry Actinomorphic – radial symmetry – regular – cut across in more than one plane & retain symmetry (gives mirror-images) Symmetry in flower structure cont’d Zygomorphic – bilateral symmetry – only one plane of symmetry – Irregular Flower evolution PRIMITIVE TRAITS Flower parts many Flower parts of indefinite number Flower parts free Flower parts spirally arranged All types of parts present Flowers bisexual Ovary superior Flower of regular symmetry Flowers conspicuous ADVANCED TRAITS Flower parts few Flower parts of definite number Flower parts fused Flower parts whorled Some whorl(s) missing Flowers unisexual Ovary inferior Flower of bilateral or irregular symmetry Flowers inconspicuous Examples of flowers with primitive and advanced traits Primitive: Nymphaea water lily Advanced Flowers: used in taxonomic classification (a) half-flower drawing (b) floral diagram ALSO: floral formula, e.g. Br, Ebrl, %, ♀♂, K5, C5 A (5) G (5) Inflorescence: cluster of flowers in a particular arrangement See info, Practical 4 in Manual Left to right: umbel, capitulum/head, spike/raceme FRUITS The use of the term fruit in Biology strictly refers to: – REPRODUCTIVE STRUCTURE formed from OVARY – as a result of FERTILIZATION of OVULE(s) ovule develops into the seed ovary develops into the fruit So, a fruit normally contains one or more seeds (depending on how many ovules were in ovary & how many of these were fertilized). At maturity, fruit consists of three layers: ✓ Outermost epicarp (or exocarp) or fruit wall or skin of the fruit ✓ Middle layer or mesocarp, may be fleshy or fibrous and dry ✓ Inner layer, the endocarp, surrounds the seed. All three layers collectively known as the PERICARP separate layers not easily distinguishable in ‘dry’ fruits Note Fruits have two ‘scars’ on opposite ends: - scar of attachment to receptacle - scar from dried/withered style. Seeds have only one scar: from attachment of ovule to placenta in ovary Fruit ‘Types’ Fruits can be categorized in four ways: FLORAL ORIGIN (number of flowers/fusion of carpels) TISSUE ORIGIN SUCCULENCE DEHISCENCE (A) FLORAL ORIGIN (1) Simple Fruit from one flower with one carpel or fused carpels, e.g. mango, apple, tomato. (2) Multiple Fruit from inflorescence: several fruits develop, merging and fusing into a single fruit body, e.g. pineapple, noni, breadfruit. (3) Aggregate Fruit from one flower with several unfused carpels, each carpel becoming a ‘fruitlet’, which fuse together (partially or mostly) e.g. sweetsop, soursop, raspberry. Simple, multiple and aggregate fruits Pictures: - Morton, J. 1987. Mango. p. 221– 239. In: Fruits of warm climates, https://hort.purdue.edu/newcrop/mort on/mango_ars.html. - Wikipedia (B) TISSUE ORIGIN On basis of the tissues, which form fruit. (1) TRUE FRUIT Develops from nothing but ovary wall – most fruits – after pollination, all other parts of flower fall off receptacle; style and stigma abscise. (2) ACCESSORY FRUIT Develops from other parts of flower as well as ovary wall – Receptacle often becomes the accessory tissue, e.g. temperate (Golden Delicious, etc.) apple, temperate (Bosch, etc.) pear, strawberry. Cashew (Anacardium occidentale) native to American tropics Accessory fruit (from pedicel and receptacle) – “cashew apple” True fruit (nut-like drupe; single, edible seed) http://www.hort.purdue.edu/newcrop/ morton/cashew_apple.html (C) SUCCULENCE, (D) DEHISCENCE (C) Fruits may also be described on basis of whether mature fruit is - fleshy/succulent (juicy) or - dry (stony, papery, woody, etc.). (D) opens to release seeds: dehiscent or remains closed: indehiscent; seeds are retained & dispersed within fruit. Sub-categories of fruit depend on: number of seeds type of ovary structure of layers of pericarp how fruit splits open (if dehiscent) (these details not covered here) Note: "fruit and nut" is botanically a ‘redundant’ expression because a nut is a fruit! Many vegetables are actually fruits, e.g. pumpkin, cucumber, egg plant, chocho. Not everything we commonly call a "nut" is a true nut. What is a NUT? - one-seeded, dry, indehiscent fruit with hard pericarp FYI (not expected to learn these): The peanut = seed from a legume. The almond ‘nut’ = seed from a drupe. The ’dry coconut’ = pit from a drupe. The Seed Reproductive structure containing new sporophyte generation. After fertilization, embryo makes initial development (usually producing a central axis with radicle, cotyledon(s) and first leaves); – integuments become the seed coat or testa. Then no further development occurs, regulated water loss → mature seed. seed is in ‘quiescent’ state (some species: dormant) dual role: - unit of dispersal - unit of perennation (survival from one growing season to next) capable of surviving adverse environmental conditions. Depending on type of nutritive tissue, seeds classified into two main types: ENDOSPERMIC (ALBUMINOUS) SEEDS Endosperm is nutritive tissue, e.g. Ricinus (eudicot), Zea (monocot) - rich in carbohydrates and sometimes lipids Endosperm occupies most of space of seed Cotyledon(s) are small Endospermic/Albuminous, e.g. corn/maize (corn grain = fruit) NOTE For grass (Poaceae) endospermic seeds: – single cotyledon called scutellum, e.g. Zea mays (corn, maize) NON-ENDOSPERMIC (EXALBUMINOUS) SEEDS Do not possess endosperm – endosperm tissue does not develop after double fertilization Instead, cotyledon(s) stores nutritive tissue, – Cotyledons occupy most space within seed, e.g. Phaseolus and other legumes Seed structure Endospermic seed a) testa (seed coat) b) endosperm c) cotyledon d) embryo axis Non-endospermic seeds above: pea; below right: avocado pear - hilum Schematic of embryo http://aob.oxfordjournals.org/content/early/2011/05/11/aob.mcr096/F1.large.jpg Seed Germination 1. Epigeal seeds germinate with cotyledons being raised above ground level as the hypocotyl elongates, e.g. Phaseolus 2. Hypogeal seeds germinate with cotyledon(s) remaining below ground level as the epicotyl elongates, e.g. Cajanus, Zea Epigeal Germination (Phaseolus vulgaris) Hypogeal Germination (Zea) Herbarium Block A, DLS, UWI Natural History Division, Institute of Jamaica Jamaica Virtual Herbarium – http://www.jamaicavirtualherbarium.com/ http://www.ibiblio.org/botnet/glossary/a_i.html http://botanydictionary.org/ http://en.wikibooks.org/wiki/Botany