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Belong to the group Phanerogams i.e., seed bearing plants. They have naked seeds (not enclosed within a fruit). They are mainly xerophytes.
Have diplontic life cycle.
Plant body is the sporophyte & the gametophytic generation is very much reduced.
Sporophyte is well differentiated into root, stem & leaves.
Stem: Thick, woody with scars of fallen leaves.
Leaves are 2 types: foliage leaves & scale leaves.
They are either monoecious or dioecious.
They are heterosporous and bear male & female cones.
Male cones are smaller in size & short lived.
They consist of spirally arranged microsporophylls.
Microsporophyll bear microsporangia inside which the microspores/pollens are produced after meiosis.
Pollen/microspore starts dividing in the microsporangium.
They produce 1-2 prothallial cells, a generative cell & a tube cell.
Further development occurs after pollination.
The generative cell divides to form body cell & stalk cell. The body cell then produces 2 male gametes. Tube cell forms the pollen tube carrying the male gametes.
FEMALE REPRODUCTIVE PART:
Female cones are larger in size.
They consist of spirally arranged megasporophylls.
Megasporophyll bear megasporangia.
Megasporangia/ovule is orthotropous type.
Inside ovule develops megaspore mother cell that undergoes meiosis to form 4 megaspores, 3 of which degenerate.
The 4th functional megaspore forms the female gametophyte, that possesses 2-8 archegonia. Egg are produced in archegonia.
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Pollination is anemophilous.
Fertilization occurs in archegonia.
Development of embryo is meroblastic.
The zygote divides to form the embryo having cotyledons, plumule & radicle.
Ovule matures into seed & the female gametophyte forms the endosperm.
Coniferopsida: e.g., Pinus, Abies, Cedrus.
Cycadopsida: e.g., Cycas, Zamia.
Ginkgopsida: e.g., Ginkgo.
Gnetopsida: e.g., Gnetum, Ephedra, Welwitschia.
Stem shows monopodial branching.
Simple, needle-shaped leaves.
2 microsporangia per microsporophyll.
Pollens possess 2 air sacs that act as wings.
pycnoxylic wood(densely packed).
Unbranched stem with a crown of leaves.
Leaves are pinnately compound.
Microsporangia develop in groups called sori in the microsporophylls.
Female cone is not formed. Megasporophylls lie scattered.
They possess largest egg, sperm & ovule.
Wood is manoxylic (not compact).
Also Read Bryophyta and Alteration of generation.
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