Phylogenetic Considerations: Ephedra, Welwitschia and Gnetum
The Gnetopsida has been studied for over a century. The scanty fossil record, restricted to the Tertiary, does not indicate the origin and relationship of this enigmatic group. The discovery of Ephedripites pollen (related to modern Gnetopsida pollen, specially Welwitschia) in the lower Cretaceous (Trevisan 1980) is significant, as it suggests that at least some member of the group was present at the time of the origin of angiosperms. According to Stewart (1983), based on fossil record, a polyphyletic origin of angiosperms from gymnosperms appears more plausible than previously presumed. As in progymnospermopsida (gymnospermous wood and pteridophytic reproduction), the preangiospermopsida (proangiosperms) could have any one, of a several combinations. Those gymnosperms, that combine a few/some angiospermic characters and form a complex from which evolutionary lines lead to the flowering plants, should be investigated for the origin of angiosperms.
KeywordsChlorophyll Cretace_ous Perforation
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