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THE VASCULAR PLANTS (vascular plants (sporophyte with cuticle, apical…
THE VASCULAR PLANTS
vascular plants
sporophyte with cuticle
apical meristems (growth from tips) on branching sporophytes
lignin – strength and rigidity
mycorrhizal associations with fungi help gather water and nutrients
efficient and effective internal transport of water and photosynthates
alternation of generations with dominant sporophyte
sporophyte is dominant
Gymnosperms
Coniferophyta, Cycadophyta, Gnetophyta, Ginkophyta
seeds have seed coat, food supply and embryo
seeds from exposed ovules (Gymno = naked)
pollen and pollen tube
the importance of conifers
cold-adapted
major economic and cultural importance
dominate key ecosystems such as boreal forest, temperate rain forest
have male and female cones - microsporangia and megasporangia
pine alternation of generations
microspore produces pollen grain which removes need of water for sperm to swim to egg, megaspore produces megagametophyte which produces eggs, sperm swim to eggs in pollen tube, fertilisation, zygote, young embryo (which is a sporophyte), tissue around embryo in seed is haploid
many vascular plants have secondary (thickening) tissue and adaptations to dry environments – e.g. pine
earliest known vascular plant
dichotomous branching (no overlapping)
few cm high
Cooksonia
sporangia at tips (an enclosure in which spores are formed)
phylum Pteridophyta
mostly ferns
alternation of generation with independent sporophyte
spores germinate, form gametophytes which are tiny and insignificant, gametophytes produce sperm (antheridium) and egg (archegonium) , fertilisation, zygote, embryo, leaf of young sporophyte, adult sporophyte (leaf we see)
cross section through fern vascular tissue shows phloem and xylem
sporophyte is less vulnerable which shows progressive evolution (in moss, gametophyte is dominant which is much more delicate and vulnerable)
phylum Lycopodiophyta
Lycopodiaceae and Selaginellaceae
heterospory
male spores small – microspores → microgametophyte → sperm
female spores large – megaspores → megagametophyte → egg (and support for the embryo)
male and female spores produced in different sporangia
specialisation of spores to reflect roles of male and female gametophytes
led to evolution of two critical developments
pollen – sperm no longer needs to swim
seeds – protects and disperses embryo
selaginella alternation of generations
microspore produces microgametophyte which produces sperm, megaspore produces megagametophyte which produces eggs, fertilisation, zygote, young embryo, heterosporous
embryo protected inside seed
other extant phyla of plants and numbers of species
with seeds
Cycadophyta – cycads – 140
Ginkophyta – Ginko – 1
Coniferophyta – conifers – 630
Gnetophyta – gnetophytes – 70
Anthophyta – flowering plants, angiosperms – 300,000
seedless
Lycopodiophyta – lycophytes 1200
Pteridophyta - ferns - 11,000