Evolution and Diversity of Plants
Mader: Biology 8th Ed.
Outline
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Evolutionary History
Alternation of Generations
Nonvascular Plants
Vascular Plants
– Seedless
– Seed
– Angiosperms
 Monocots and Dicots
 Flowers
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Evolutionary History of Plants
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Plants are thought to have
evolved from freshwater algae
over 500 million years ago.
Marked by four evolutionary
events associated with four
major groups of plants…..
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Evolutionary History of Plants
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Nonvascular Plants
 nourishment of a multicellular embryo
within the body of the female plant.
Seedless Vascular Plants
 Advent of vascular tissue.
Gymnosperms and Angiosperms
 Produce seeds.
Flowering Plants
 Attract pollinators that give rise to fruits.
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Alternation of Generations
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All plants have a life cycle that includes
an alternation of generations.
– Two multicellular individuals
alternate, each producing the other.
Sporophyte = diploid generation.
Gametophyte = haploid generation.
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Alternation of Generations
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Alternation of Generations
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Alternation of Generations
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Sporophyte (2n) is named for its
production of spores by meiosis.
– Spore is haploid reproductive cell.
Gametophyte (n) is named for its
production of gametes.
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Reduction in Size of Gametophyte
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Alternation of Generations
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Appearance of generations varies widely.
– In ferns, female portions are archegonia
and are fertilized by flagellated sperm.
– In angiosperm, female gametophyte
(embryo sac), consists of an ovule.
 Following fertilization, ovule becomes
seed.
– In seed plants, pollen grains are mature
sperm-bearing male gametophytes.
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Protection of Eggs and Embryos
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Other Terrestrial Adaptations
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Vascular tissue transports water and
nutrients to the body of the plant.
Cuticle is an effective barrier to water
loss.
Stomata bordered by guard cells that
regulate opening, and thus water loss.
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Leaves of Vascular Plants
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Nonvascular Plants
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Do not have true roots, stems, or leaves.
Gametophyte is dominant generation.
 Produces eggs in archegonia and
flagellated sperm in antheridia.
 Sperm swim to egg in film of water.
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Nonvascular Plants
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Hornworts (phylum Anthocerophyta) have
small sporophytes that carry on
photosynthesis.
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Nonvascular Plants
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Liverworts (phylum Hepatophyta) have
either flattened thallus or leafy appearance.
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Nonvascular Plants
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Mosses (phylum Bryophyta) usually have a
leafy shoot, although some are secondarily
flattened.
– Can reproduce asexually by
fragmentation.
– Dependent sporophyte consists of foot,
stalk, and sporangium.
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Moss Life Cycle
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Vascular Plants
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Xylem conducts water and dissolved
minerals up from roots.
Phloem conducts sucrose and other organic
compounds throughout the plant.
Lignin strengthens walls of conducting cells
in xylem.
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Vascular Tissue
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Seedless Vascular Plants
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Club Mosses (phylum Lycophyta)
– Typically, branching rhizome sends up
short aerial stems.
– Leaves are microphylls (have only one
strand of vascular tissue).
– Sporangia occur on surfaces of
sporophylls.
 Grouped into club-shaped strobili.
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Club Mosses
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Seedless Vascular Plants
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Ferns and Allies
– Horsetails (phylum Sphenophyta)
 Rhizome produces tall aerial stems.
 Contains whorls of slender, green
branches.
 Small, scalelike leaves also form whorls
at the joints.
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Horsetail
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Ferns
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Whisk Ferns (phylum Psilotophyta)
– Branched rhizome has rhizoids.
– Mutualistic mycorrhizal fungus helps
gather nutrients.
Ferns (phylum Pterophyta)
– Large conspicuous fronds.
 Divided into leaflets.
 Dominant sporophyte produces
windblown spores.
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Whisk Ferns and Ferns
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Fern Life Cycle
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Fern Life Cycle
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Seed Plants
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Seed plants are the most plentiful plants in
the biosphere.
– Seed coat and stored food allow an
embryo to survive harsh conditions during
long period of dormancy.
– Heterosporous
 Drought-resistant pollen grains.
 Ovule develops into seed.
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Gymnosperms (naked seeds)
Gymnosperms have ovules and
seeds exposed on the surface of
sporophylls.
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Conifers
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Conifers, as well as other gymnosperm
phyla, bear cones.
– Tough, needlelike leaves of pines
conserve water with a thick cuticle and
recessed stomata.
 Considered a “soft” wood because it
consists primarily of xylem tissue.
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Conifers
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Pine Life Cycle
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Pine Life Cycle
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Cycads
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Cycads (phylum Cycadophyta) have large,
finely divided leaves that grow in clusters at
the top of the stem. Oldest of the
gymnosperms (about 320 million years ago)
– Pollen and seed cones on separate plants
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Ginkgoes
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Ginkgoes (phylum Ginkgophyta)
– are dioecious (male and female plants)
with some trees producing seeds and
others producing pollen.
– One surviving species =Gingko biloba
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Gnetophytes
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Gnetophytes (phylum Gnetophyta)
believed to be closest to angiosperms
because of similarity in xylem tissue and
some even produce nectar for pollinators!
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Angiosperms (covered seeds)
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Angiosperms (phylum Anthophyta)
– are an exceptionally large and successful
group of plants.
 Produce flowers
 Seeds are enclosed in a fruit.
 Oldest fossils are 130 million years old
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Monocots and Eudicots
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Two classes of flowering plants.
– Monocotyledones (Monocots)
 One cotyledon in seed.
– Eudicotyledones (Dicots)
 Two cotyledons in seed.
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The Flower
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Penducle (flower stalk) expands at tip into a
receptacle.
– Bears sepals, petals, stamens, and
carpels, all attached to receptacle in
whorls.
– Calyx (collection of sepals) protect flower
bud before it opens.
– Corolla (collection of petals).
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The Flower
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Each stamen consists of an anther and a
filament (stalk).
Carpel has three major regions.
 Ovary - Swollen base.
 Fruit
 Style - Elevates stigma.
 Stigma - Sticky receptor of pollen grains.
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Flowering Plant Life Cycle
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Flowering Plant Life Cycle
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Flowers and Diversification
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Wind-pollinated flowers are usually not
showy.
Bird-pollinated flowers are often colorful.
Night-blooming flowers attract nocturnal
mammals or insects.
– Usually white or cream-colored.
Fruits of flowers protect and aid in dispersal.
– Utilize wind, gravity, water, and animals
for dispersal.
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