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Kingdom Plantae: Angiosperms 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

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Kingdom Plantae:Angiosperms


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Angiosperms (Phylum Anthophyta)

  • Largest group of plants: 250,000 species!

  • Still more to be discovered.......


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Finding New Species

  • True New Discoveries: Bibb Glades, AL

  • Limestone openings in forest

Bibb County


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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


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Angiosperms (Phylum Anthophyta)

  • Are land plants, so make embryos, have multicellular gametangia with sterile jackets, etc.


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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).


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Angiosperms (Phylum Anthophyta)

  • Are seed plants, so:

  • 1) Are heterosporous (make megaspores and microspores in specialized sporangia)

  • 2) Make pollen grains, ovules/seeds.


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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.


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The flower

  • Flower is short stem with modified leaves


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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)


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The flower

  • Modified leaves:

    • easy to see for sepals (leaf-like)


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The flower

  • Modified leaves:

    • stamens? modified leaf bearing microsporangia (these now pollen sacs)

    • reduce leaf blade to leave microsporangia.


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The flower

  • Modified leaves:

    • pistil? modified leaf called carpel, bearing megasporangia in ovules

    • “ovule taco”


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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)


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The flower

  • Modified leaves:

    • petals? modified stamens, that have lost sporangia and become flat and colored.


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Life Cycle

  • Overview:

Fig. 42.2


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Life Cycle

  • Part 1: Making gametophytes (in anther and ovule)

  • Ovule: integumented megasporangium.

  • Notice 2 integument layers (gymnosperms had only 1)

  • Nucellus=megasporangium.


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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.


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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.


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Life Cycle

  • Part 1: Making gametophytes (in anther and ovule)

  • Note: microsporocyte= microspore mother cell, megasporocyte= megaspore mother cell


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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.


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Life Cycle

  • Double fertilization

  • Creates zygote (2n): 1 sperm + egg

  • Creates endosperm (3n): 1 sperm + 2 polar nuclei.


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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).


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Life Cycle

  • Seed or seeds develop inside of ovary to become fruit

  • Ovary wall in pistil becomes pericarp in fruit.


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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.


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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


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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


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Floral variation

  • Quiz: To which Class does each species belong?

Malva flower

Sagittaria flowers


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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


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Floral variation

  • Fusing of petals can form floral tube (nectar made at bottom)

  • Only long-tongued pollinators can reach it.

Anisacanthus (Acanthaceae) flower


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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


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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.


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Persimmon fruits

Floral variation

  • Example of dioecious species: Persimmon (Diospyros)

Pistillate

flower

Staminate

flower


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Floral variation

  • Some flowers are missing one or more sets of basic parts: incomplete flowers

  • Note that all imperfect flowers are therefore incomplete!


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Floral variation

  • Floral symmetry:

  • Radial: can be divided into similar halves by several planes

  • Bilateral: can be divided into mirror images by 1 plane.


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Floral variation

  • Ovary position

  • Superior: other parts attach below ovary (hypogynous: “hypo-” =below, “gyn-” =female)


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Floral variation

  • Example of superior ovary in a lily flower (ovary is E)


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Floral variation

  • Ovary position

  • Perigynous: ovary superior, but cup formed of fused sepals, petals, stamens around it.


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Floral variation

  • Ovary position

  • Inferior: other parts attach above ovary (epigynous: “epi-”=above, “gyn-”=female)


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Floral variation

  • Example of inferior ovary: squash flower (this one is pistillate)

Ovary


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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


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Floral variation

  • Flowering dogwood (Cornus florida)

  • Inflorescence, white structures are modified leaves (bracts) that act like petals.

Closeup showing individual

greenish flowers

Inflorescence


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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.


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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


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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).


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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


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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


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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


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Pollination

  • Style of flower as “selective racetrack”

  • Is there evidence that this works?

  • Example, Coyote melon

  • Gourd growing in desert


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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).


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Pollination

  • Style of flower as “selective racetrack”

  • Other studies with some crop plants have shown similar results.


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