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Transcript
Green Plants Flowering Plants Seed Plants Vascular Plants Land Plants PHYLOGENETIC OVERVIEW Green Plants Angiosperms: flowering plants – ~235,000 species; are the dominant plants on Earth. – Wide variety of sizes and forms, from small herbaceous plants to huge trees – Flowers may be conspicuous or cryptic – Are vascular plants that reproduce sexually by forming flowers, and after a double fertilization process , produce seeds within fruits – Possess efficient water-conductive cells called vessel elements in xylem; efficient sugar-conducting cells called sieve tube members in the phloem Double Fertilization: The Embryo Sac • Angiosperms are heterosporous • Produce microspores and macrospores • Megasporocyte in ovule undergoes meiosis to produce 4 1n megaspores • 3 disintegrate – one divides by mitosis to produce the female gametophyte called the embryo sac. – Most commonly the embryo sac contains 7 cells with 8 1n nuclei – 6 have 1 nucleus – one of the six is the egg; a central one has two polar nuclei • All cells but the egg and the polar nucleus cell disintegrate Double Fertilization Flowering Plant Evolution Spermatophytes -- Seed Plants “Gymnosperms” Gnetophytes Medullosa Lyginopteris Welwitschia Ephedra Conifers Gnetum Cycads Angoisperms Ginkgos (flowering plants) Reticulate venation reduced gametophytes Carpel, endosperm, reduced gametophytes Mesozoic Seed Ferns, etc. ? >325 MYBP Bi-radial seed symmetry, sealed micropyle >360 MYBP IMPACT OF NEW DATA Loss of cupule, loss of lagenostome column Seed, axillary branching Spermatophytes: Hypotheses of Seed Plant Phylogeny Cyc Gin Con Gne Ang Con Gne “anthophyte” hypothesis Pineaceae Cyc Ang “gnetifer” hypothesis Gne Other Conifers Gin Cyc “gnepine” hypothesis IMPACT OF NEW DATA Gin Ang Ang = Angiosperms Cyc = Cycads Gin = Ginkos Gne = Gnetophytes Con = Conifers Spermatophytes: Hypotheses of Seed Plant Phylogeny Phytochrome genes 1557 base pairs 74 taxa S. Mathews et al. Conifers Ginkos Cycads Gnetophytes Angiosperms Phytochrome duplication event new hypothesis IMPACT OF NEW DATA Flower Structure The Reproductive Apparatus • The reproductive structures arise from whorls inside the petals • Stamens are the structure s that hold the pollen-bearing anthers – Male reproductive component – Have a stalklike filament – In the anthers, meiosis produces microspores that develop into pollen – Each pollen grain develops into two cells – one divides to produce the sperm cells, or male gametes – while the other produces the pollen tube through which sperm cells travel to the ovum The Female Reproductive Apparatus • Centermost whorl is the carpels – Also called the pistil – 3 sections to the pistil – • The stigma, where pollen lands • The style, or long structure through which pollen tube grows • The ovary, which contains one or more ovules, which in turn develop into embryos when fertilized A flower Pistil Structure • Pistils may be simple or compound • Nearly always have stigma, style and ovary structure • Simple has single carpel • Compound has several carpels fused together The Flower • Reproductive shoots – usually on a stem; flower is referred to as the inflorescence • Four parts arranged in whorls; i.e. circles – sepals, petals, stamens and carpels – Complete flowers have all four parts – Incomplete flowers have one or more parts missing • Held on a stalk called a peduncle • Male parts are the stamens; female the carpels • Sepals are lowermost and outermost whorl – Leaf like, often green – Cover flower when in bud – All sepals together called the calyx • Petals are the whorl above the sepals – Broad, flat and thin – Often brightly colored – Petals referred to as the corolla Amborella Water lily Evolution of Flowers • Generally accepted that flower components are all derived from leaves • This seems to be clearly indicated for the plant Drimys piperita. The carpel looks like a folded leaf Angiosperms -- Flowering Plants “Dicotyledons” Magnoliids Nymphaeales Amborella Magnoliales Austrobaileyales Canellales Laurales Chloranthaceae Piperales Eudicots Ceratophyllum Monocots tricolpate pollen 1 cotyledon >125 MYBP postgenital fusion of carpel margins (?), plicate carpels vessels >140 MYBP PHYLOGENETIC OVERVIEW Carpel, endosperm, reduced gametophytes The Sporophyte Adaptations • The sporophyte – the emergent and most obvious part of the plant, has undergone enormous adaptation, all of which aid in survival in a given region; for example: • Cacti • Trees • Lilies • Vines • Shrubs Cotyledons Ginger Grass Orchid Monocots – Palms, grasses, orchids, irises, onions and lilies are all monocots – Mainly herbaceous with long narrow leaves with parallel veins – Flowers in threes or groups of three – Monocots have a single cotyledon, or embryonic seed leaf and endosperm, a nutritive tissue in the mature seed A Second Class: The Dicots • Dicots (Class Dicotyledones) – Oaks, roses, mustards, cacti, blueberries and sunflowers are all dicots – Herbaceous or woody – Typically broader leaves than monocots – Flower parts usually in fours or fives – Two cotyledons in the seeds Polygala Buttercup Water lotus Monocots and “Dicots” • Typical features of monocots and dicots Feature Dicot Monocot Seeds Embryo w/2 cotyledons Embryo w/ 1 cotyledon Flower parts In fours/fives In threes Pollen grains 3 furrows/pores 1 furrow/pore Leaf venation Netted Parallel Vascular bundles in stem Arranged in ring Scattered or complex Roots Taproot system Fibrous roots Secondary growth (wood, bark) Often present Absent Seeds and Fruit • Each seed contains the embryo and its nutritive endosperm and is surrounded by a seed coat • As seed develops, the ovary wall may thicken and entirely surround the seed(s) • The ovary becomes a fruit • Fruits protect the seed from desiccation and also aid in dispersal Adaptations of Flowering Plants • Seed production is advantageous to longevity of the genetic material and dispersal • Closed carpels that develop to make fruit aid in dispersal also via animals that eat the fruit • Pollen is well-adapted to cross-fertilization via bees, bats, birds, etc • Flowers attract pollinators • Angiosperms have improved water and sugar transport in the xylem and phloem compared to gymnosperms and seedless vascular plants • Broad leaves, well-developed roots that can store as well as collect nutrients, critical to success Evolution of Seed Plants • Molecular analysis suggests . . . • Monocots are monophyletic • Dicots are paraphyletic – containing the common ancestor and some but not all of the descendents.
