1 Answer | Add Yours
The gnetophyta, named for the genus Gnetum (Ephedra and Welwitschia are the other two extant genera), is an ancient group that has characteristics of both angiosperms and gymnosperms. This division of land plants first appears in the fossil record during the Triassic, and was widespread during the Carboniferous.
Gnetophyta are similar to angiosperms because both groups have vessel elements in the xylem, a feature lacking in conifers and cycads. Like the angiosperms, Welwitschia and Gnetum also demonsrate double fertilization; however in angiosperms, this results in an embryo and its associated endosperm material arising from two separate sperm, whereas in gnetophytes the one embryo develops into the seed and the other is aborted. Additionally,the gnetophyte egg migrates toward the pollen tube, an unusual event only seen in this group.
The reproductive structures of the gnetophytes are generally considered to be flower-like. This group also demonstrates netted venation similar to that found in angiosperms.
We’ve answered 319,202 questions. We can answer yours, too.Ask a question