<P> Gnetaceae Gnetum Welwitschiaceae Welwitschia Ephedraceae Ephedra </P> <Tr> <Td_colspan="2"> Distribution, separated by genus: Green--Welwitschia Blue--Gnetum Red--Ephedra Purple--Gnetum and Ephedra </Td> </Tr> <P> Gnetophyta is a division of plants, grouped within the gymnosperms (which also includes conifers, cycads, and ginkgos), that consists of some 70 species across the three relict genera: Gnetum (family Gnetaceae), Welwitschia (family Welwitschiaceae), and Ephedra (family Ephedraceae). Fossilized pollen attributed to a close relative of Ephedra has been dated as far back as the Early Cretaceous . Though diverse and dominant in the Tertiary, only three families, each containing a single genus, are still alive today . The primary difference between gnetophytes and other gymnosperms is the presence of vessel elements, a system of conduits that transport water within the plant, similar to those found in flowering plants . Because of this, gnetophytes were once thought to be the closest gymnosperm relatives to flowering plants, but more recent molecular studies have largely disproven this hypothesis . </P> <P> Though it is clear they are all closely related, the exact evolutionary inter-relationships between gnetophytes are unclear . Some classifications hold that all three genera should be placed in a single order (Gnetales), while other classifications say they should be distributed among three separate orders, each containing a single family and genus . Most morphological and molecular studies confirm that the genera Gnetum and Welwitschia diverged from each other more recently than they did from Ephedra . </P>

List 2 characteristics that separate the gnetophyta from the other 3 phyla of gymnosperms
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