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Seed Plants I : Seed Plants Without Flowers ("Gymnosperms")…
Seed Plants I : Seed Plants Without Flowers
("Gymnosperms")
Concepts
Lignophytes
The cambium arose just once, in one group of plants that then give rise to a monophyletic group of woody plants.
Spermatophytes
Seed plants
Monoxylic wood
very soft, spongy, parenchymatous wood
Pycnoxylic wood
hard, strong wood with little parenchyma
Gymnosperms
They have naked ovules located on flat sporophylls.
Angiosperms
They are flowering plants with carpels
Division
Progymnospermophyta: Progymnosperms
Order
Aneurophytales
They have more relictual progymnosperms.
Archaeopteridales
Reproduction is heterosporous.
Evolution of Seeds
Megasporangium
is surrounded by a layer of tissue called integument.
Micropyle
a hole in the integument which permits sperm cells to swim to the egg after the megaspore had developed into a megagametophyte and had produced eggs.
Pollen chamber
microspores settle here.
Pteridospermophyta: Seed ferns
Pteridospermophyta , all extinct
evolved from Aneurophytales
Cycadophyta , cycads extant
Pollen cone
Microsporophyll in cycads may bear many microsporangia
Sperm cells of cycads have hundreds of flagella and must swim to the egg cell.
Cycadeoidophyta , cycadeoids, all extinct
Vegetatively, cycadeoids such as Cycadeoidea were similar to cycads. They had a broad cortex and a tough outer protective layer formed by persistent leaf bases.
Coniferophyta: Conifers
Order
Voltziales
Family Voltziaceae , Lebachia
Coniferales
Family
Pinaceae
Pine
Two types of shoots
Long shoots
Short shoots
Simple cones
Araucariaceae
Agathis
Taxodiaceae
Sequoia
Podocarpaceae
Podocarpus
Cupressaceae
Juniperus
Cephalotaxaceae
Cephalotaxus
Taxales
Family , Taxaceae
Taxus
Ginkgophyta: Maidenhair Tree
Ginkgo leaves are broad.
dichotomous venation like leaves of cycads and seed ferns.
Microsoporophylls occur in small, cone like clusters
Ovules occur in pairs at the end of a stalk-like megasporophyll.
Gnetophyta
strongly resembles dicots, having broad leaves and woody stems.
Ovules are not borne in cones.
