The Gnetales are a class apart, including three living genera, of which we know next to nothing as regards their past history or line of descent.
Although there are several morphological features in the three genera of Gnetales which might seem to bring them into line with the Angiosperms, it is usual to regard these resemblances as parallel developments along distinct lines rather than to interpret them as evidence of direct relationship.
Flowers unisexual, except in a few cases (Gnetales) without a perianth.
Secondary xylem and phloem produced by a single cambium, or by successive cambial zones; no true vessels (except in the Gnetales) in the wood, and no companioncells in the phloem.
The three existing genera, usually spoken of as members of the Gnetales, differ from one another more than is consistent with their inclusion in a single family; we may therefore better express their diverse characters by regarding them as types of three separate families-0) Ephedroideae, genus Ephedra; (2) Welwitschioideae, genus Welwitschia; (3) Gnetoideae, genus Gnetum.