Gymnosperms:

There are 4 phyla of gymnosperms with living species:

Cycadophyta: cycads-have male and female trees	Gingkophyta- maidenhair tree
Coniferophyta: conifers-575 species include pines, firs, spruces, hemlocks etc. gingkoes	Gnetophyta: only 3 genera

 

General Characteristics of gymnosperms: 1. The name gymnosperms means "naked seed": their ovules and seeds are exposed on the surface of sporophylls - no such protective fleshy coating as we will find with the angiosperms. 2. Polyembryony; Usually the female gametophyte produces several archegonia leading to the production of many eggs, but only 1 embryo survives per seed. 3. Unlike their earlier ancestors, gymnosperm sperm do not swim to the egg using water as the transfer vector. Instead the male gametophyte is a 'pollen grain' which is carried by wind or animal to the female gametophyte. This process is called pollinaton. After pollination the pollen grain produces a pollen tube which grows to the egg's vicinity. In cycads and ginkgo, eventually the flagellated sperm do swim to the egg; in the conifers and gnetophytes the tube grows directly to the egg so sperm are nonmotile... this means a release from a dependency on moisture for reproduction.. important in the drier climate which formed after the carboniferous period.

 

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Cycadophyta:

Gingkophyta-

Gnetophyta:

Gnetophyte: ephedra

Gnetophyte: weltwitschia

Coniferophyta:

Introduction