This subdivision consists of 3 living genera and approximately 70 species, some quite unusual and still very apparent today:
1. An interesting feature of all gnetophytes is the presence of both tracheids and vessel elements in their xylem tissue. Most flowering plants contain vessel elements, too, providing evidence to some botanists that the Gnetophyta might have been ancestral to angiosperms.
Gnetophyta's unique fertilization feature is that a tube grows from the eggs to unite with the pollen tubes in order for fertilization to take place between the gametophytes. The sperm themselves are not motile, like we see in the cycads and gingko.
This is the only type of gymnosperm that undergoes double fertilization, however no endosperm forms and the 2nd egg fertilized disintegrates. Also like the angiosperms, some of the species produce nectar and are visited by insects.
It is thought that it is this group may have evolved the angiosperms- but certainly not any of the extant species .. most likely an early progenitor of both this group and the angiosperms.
|Cycadophyta:||Gingkophyta-||Gnetophyta:||Gnetophyte: ephedra||Gnetophyte: weltwitschia||Coniferophyta:||Introduction|