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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
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New Discoveries: Bibb Glades, AL
Limestone openings in forest
Surveyed for plants in 1990’s
8 new taxa discovered.
Cahaba paintbrush
Ketona tickseed
Cahaba torch
Angiosperms (Phylum Anthophyta)
• Are land plants, so make embryos, have
multicellular gametangia with sterile jackets,
etc.
Angiosperms (Phylum Anthophyta)
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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.
• Overview:
Fig. 42.2
Life Cycle
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
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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.
Floral variation
Persimmon fruits
• 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.
Inflorescence
Closeup showing individual
greenish flowers
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)
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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
• 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!
Pollen grains
stigma
style
ovary
2 ovules
Pollination
• 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.
2 ovules
Pollen grains
stigma
style
ovary
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).
Pollination
• Style of flower as “selective racetrack”
• Other studies with some crop plants have shown
similar results.