Vascular Plants: Success on Land
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A. Carboniferous Forests:
286286-360 m.y.a.
‹ Lower Vascular Plants: Seedless
Plants
‹ Div. Pterophyta: Fern Life Cycle
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Lower Vascular Plants: Seedless Plants
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Cooksonia:
Cooksonia: 425 mya (Silurian) dichotomous
branching, terminal sporangia, no true roots or
leaves, short, marsh habitat
B. Permian Pressures: 280280245 m.y.a.
‹ Higher Vascular Plants: Seed
Plants
‹ 5 Arid Adaptations
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C. The Gymnosperms
‹ General Features
‹ Conifer Life Cycle
Artist’s conception of a Carboniferous forest
based on fossil evidence
Pteridophytes: 2 Divisions of early
(lower) vascular plants
Lycophyta:
Lycophyta: club mosses and ground pines
„ Pterophyta: horsetails, ferns, whisk ferns
(not shown)
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Division Pterophyta: mostly
Ferns
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The life cycle of a fern
Shift in dominance: sporophyte
dominant, reduced and indep.
indep.
gametophyte
homosporous (some heterospory)
heterospory)
Spores represent the dispersal
stage
protected embryophyte
flagellated sperm
Xylem and phloem poorly
differentiated, esp. phloem, no
lignin
Leaves, true roots in sporophyte
stage
1
Life cycle of a fern: mature fern
Fern sporophyll, a leaf specialized for
spore production
Life cycle of a fern: sporangium
Fern sporophyll, a leaf specialized for
spore production
Life cycle of a fern: sorus
Life cycle of a fern: mature sporangium
2
Life cycle of a fern: germinating
Higher Vascular Plants: Permian
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Seed Plants: Gymnosperms and
Angiosperms
Adaptations to a dryer environment:
‹ More specialized vascular tissue
‹ Reduction and retention of the
gametophyte
) Spores for dispersal?
) Diploid dominance?
‹ Complete change from
homospory to heterospory
‹ Pollen
‹ Seeds: dispersal, multicellular,
nucellus,
nucellus, protected embryophyte
The advantages of seeds:
1. Multicellularity
„ 2. Female gametophyte = egg + nutrients
„ 3. Protected & nourished embryophyte
„ 4. Delayed development
„ 5. Multicellular dispersal tool
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Life cycle of a fern: gametophyte
Three variations on
gametophyte/sporophyte
relationships
Hypothetical phylogeny of the seed
plants
3
Gymnosperms: 4 Divisions
Phylum Ginkgophyta: Ginkgo biloba
Cycadophyta,
Cycadophyta, Ginkophyta,
Ginkophyta,
Gnetophyta and
Coniferophyta
„ Conifers: General Features
‹Largest division
‹Commercial value
‹Evergreen status
‹Needles: leaf adaptation
to arid conditions,
continuous growth
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Phylum Cycadophyta: cycads
Ginkgo: Male (left), female (right)
Phylum Gnetophyta: Welwitschia
Phylum Gnetophyta: Gnetum
4
Phylum Gnetophyta: Ephedra
Gymnosperm Life Cycle
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Phylum Coniferophyta: Wollemia pine
The life cycle of a pine
Pine tree = mature sporophyte
Heterospory = male and female cones
‹ Male cone: microsporangia divide meiotically
haploid microspores
mitosis yields 2 celled pollen
grains = immature male gametophyte
‹ Female cone: ovule contain megasporangia
megasp.
megasp.
Mother cells undergo meiosis
one n cell survives
1000’
female gametophyte (also
1000’s of mitoses
contains 22-3 archegonia w/ one egg cell each
‹ Pollination
‹ Fertilization: mitosis of pollen grain yields 2 sperm
nuclei
pollen tube
both injected into one egg,
one disintegrates and diploid zygote forms
‹ Seed: 3 generations under one roof.
‹ Cycle time = 1010-12 years
The life cycle of a pine
The life cycle of a pine
5
Pine embryo
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