Angiosperms (Phylum Anthophyta) • Largest group of plants: 250,000 species! • Still more to be discovered.......
Finding New Species • True New Discoveries: Bibb Glades, AL • Limestone openings in forest Bibb County
Finding New Species • New Discoveries: Bibb Glades, AL • Limestone openings in forest • Surveyed for plants in 1990’s • 8 new taxa discovered. Cahaba paintbrush Cahaba torch Ketona tickseed
Angiosperms (Phylum Anthophyta) • Are land plants, so make embryos, have multicellular gametangia with sterile jackets, etc.
Angiosperms (Phylum Anthophyta) • Are vascular plants, so: • 1) Have vascular tissue (xylem, phloem) • 2) Make cuticle and stomata • 3) Make true stems, roots, leaves (megaphylls).
Angiosperms (Phylum Anthophyta) • Are seed plants, so: • 1) Are heterosporous (make megaspores and microspores in specialized sporangia) • 2) Make pollen grains, ovules/seeds.
Angiosperms • Differ from gymnosperms by: • 1) Producing pollen and ovules/seeds in flower (new structure) • 2) Ovules/seeds made in fruit (new structure) • 3) Life cycle: Double fertilization occurs (two fertilization events when pollen tube reaches female gametophyte) • 4) Ovule has 2 integument layers, rather than 1.
The flower • Flower is short stem with modified leaves
The flower • Additional flower terms: • Androecium: All of the stamens • Gynoecium: All of the pistils • Perianth: All of the petals and sepals (helpful when sepals and petals alike)
The flower • Modified leaves: • easy to see for sepals (leaf-like)
The flower • Modified leaves: • stamens? modified leaf bearing microsporangia (these now pollen sacs) • reduce leaf blade to leave microsporangia.
The flower • Modified leaves: • pistil? modified leaf called carpel, bearing megasporangia in ovules • “ovule taco”
The flower • Modified leaves: • pistils can be simple (1 carpel) or compound (> 1 fused carpels) • generally, number of chambers (locules) in ovary = number carpels. 1 locule= 1 carpel (simple) 3 locules= 3 carpels (compound)
The flower • Modified leaves: • petals? modified stamens, that have lost sporangia and become flat and colored.
Life Cycle • Overview: Fig. 42.2
Life Cycle • Part 1: Making gametophytes (in anther and ovule) • Ovule: integumented megasporangium. • Notice 2 integument layers (gymnosperms had only 1) • Nucellus=megasporangium.
Life Cycle • Pollen grain: immature microgametophyte • Made by meiosis in sacs (microsporangia, or pollen sacs) in anther of stamen • When pollen released, typically has only 2 haploid cells in it.
Life Cycle • Embryo sac: mature megagametophyte • Very reduced: 7 cells and 8 nuclei. • Central cell has 2 haploid nuclei (polar nuclei) • One cell is egg. Note no archegonium made.
Life Cycle • Part 1: Making gametophytes (in anther and ovule) • Note: microsporocyte= microspore mother cell, megasporocyte= megaspore mother cell
Life Cycle • Pollen grain with only 2 cells (immature microgametophyte) • Arrives on stigma (instead of at ovule as in gymnosperms) • Pollen tube (contains 2 sperm cells: no flagella present, don’t swim) grows to ovule.
Life Cycle • Double fertilization • Creates zygote (2n): 1 sperm + egg • Creates endosperm (3n): 1 sperm + 2 polar nuclei.
Life Cycle • Zygote grows into embryo, endosperm also grows • Embryo uses endosperm for nourishment (eats sibling) • Seed: baby plant (embryo), in box (seed coat, made from integuments), with its lunch (endosperm).
Life Cycle • Seed or seeds develop inside of ovary to become fruit • Ovary wall in pistil becomes pericarp in fruit.
Life Cycle • Differences from gymnosperms: • 1) Pollen arrives at stigma rather than ovule • 2) Gametophytes reduced still further: pollen grain only 2 cells, megagametophye 7 cells/8 nuclei and no archegonium • 3) Double fertilization creates zygote and triploid endosperm • 4) Embryo digests endosperm • 5) Seed coat made from 2 integuments • 6) Seeds mature in ovary to make fruit.
Floral variation and evolutionary trends • Earliest fossil flowers show: • many parts • parts spirally arranged rather than in whorls (rings) • parts separate, not fused to similar or different parts • ovary superior • radial symmetry. Magnolia flower
Floral variation • Some flowers have reduced numbers of parts • 4’s and 5’s: Class Dicotyledonae (dicots) • 3’s and multiples of 3: Class Monocotyledonae (monocots). Magnolia flower
Floral variation • Quiz: To which Class does each species belong? Malva flower Sagittaria flowers
Floral variation • Parts may be fused • Example, petals fused to each other • Like parts fused: connation (ex., petals to petals) • Unlike parts fused: adnation (ex., stamens to petals) Snapdragon flower
Floral variation • Fusing of petals can form floral tube (nectar made at bottom) • Only long-tongued pollinators can reach it. Anisacanthus (Acanthaceae) flower
Floral variation • Flowers with stamens and pistils: perfect flowers • Some flowers imperfect. Either pistillate (have pistil) or staminate (have stamens). Pistillate flowers of Sagittaria Staminate flowers of Sagittaria
Floral variation • Note: some species make pistillate flowers and carpellate flowers on separate individuals • This termed dioecious • Monoecious is when both sexes on same individual.
Persimmon fruits Floral variation • Example of dioecious species: Persimmon (Diospyros) Pistillate flower Staminate flower
Floral variation • Some flowers are missing one or more sets of basic parts: incomplete flowers • Note that all imperfect flowers are therefore incomplete!
Floral variation • Floral symmetry: • Radial: can be divided into similar halves by several planes • Bilateral: can be divided into mirror images by 1 plane.
Floral variation • Ovary position • Superior: other parts attach below ovary (hypogynous: “hypo-” =below, “gyn-” =female)
Floral variation • Example of superior ovary in a lily flower (ovary is E)
Floral variation • Ovary position • Perigynous: ovary superior, but cup formed of fused sepals, petals, stamens around it.
Floral variation • Ovary position • Inferior: other parts attach above ovary (epigynous: “epi-”=above, “gyn-”=female)
Floral variation • Example of inferior ovary: squash flower (this one is pistillate) Ovary
Floral variation • Some flowers assembled into groups of flowers: inflorescence • Special inflorescence type: head • Example, sunflower and its relatives • Ray flowers have large fused petals (corollas fused), disk flowers small and crowded. ray flowers disk flowers
Floral variation • Flowering dogwood (Cornus florida) • Inflorescence, white structures are modified leaves (bracts) that act like petals. Closeup showing individual greenish flowers Inflorescence
Pollination • Why flowers so varied? Many form mutualism with animals to achieve pollination • Most gymnosperms are wind pollinated • Must make lots of pollen in hope some reaches ovule in female (seed) cone. Most pollen falls to ground within 100 m of plant.
Pollination • Some flowering plants are wind pollinated too • Ex, most grasses (corn, wheat, etc.), many temperate zone flowering trees (oaks, willows, maples, hickories) • Flowers usually small, no petals, no nectar, make lots of pollen. Small, greenish grass flowers
Pollination • Most flowering plants are pollinated by animals • This usually viewed as mutualism (where both species benefit) • Plant gets pollen transferred • Animal gets “reward” • Pollen: high in protein • Nectar: sugary fluid produced by nectar glands (nectaries) in flower • Oils/Resins: some used as construction materials, “cologne” (male bee uses oil as female attractant).
Pollination • Benefits of animal pollination • 1) Directed dispersal of pollen. Animal can take pollen directly to where plant wants it to go (stigma of flower of same species). Less waste of pollen
Pollination Pollen grains • Benefits of animal pollination • 2) Style of flower as “selective racetrack” • Keep in mind that 1 pollen grain can fertilize 1 ovule • Suppose 5 pollen grains arrive on stigma • Start to make pollen tubes • How many can fertilize an ovule? • 2! First 2 to arrive! • Rest? LOSERS! stigma style ovary 2 ovules
Pollination Pollen grains • Benefits of animal pollination • 2) Style of flower as “selective racetrack” • Pollen tubes are haploid (1n) • Haploid means only 1 allele (gene version) for every trait • If an allele is recessive, then it will be expressed (can’t be masked by another, dominant allele) • So, fittest (fastest) pollen grains mate • Inferior genes don’t get passed to offspring. stigma style ovary 2 ovules
Pollination • Style of flower as “selective racetrack” • Is there evidence that this works? • Example, Coyote melon • Gourd growing in desert
Pollination • Style of flower as “selective racetrack” • Study done in 2000 showed that • 1) takes 900 pollen grains to fully pollinate flower • 2) 1 pollinator visit puts 650 grains/flower. By 2 hours, >4000 grains deposited on stigma • 3) Seeds produced from over-pollinated flowers produced more vigorous seedlings (compared to seeds from flowers with <900 pollen grains on stigma).