The Gnetales is a group of around 65 to 75 gymnosperm seed plants in just three extant genera: Ephedra, Gnetum, and Welwitschia. At one time the Gnetales were believed to be the sister group to the angiosperms (flowering plants), but this relationship is inconsistent with most recent molecular phylogenetic analyses, which have variously placed the group as sister to all the extant conifers, as sister to the Pinaceae within the conifers, or as sister to all the non-Pinaceae conifers within the conifers.
Ephedra includes around 50 species, which are distributed in both temperate and subtropical arid environments in the Northern Hemisphere and South America. About a dozen of these species, often known as Mormon Tea, are found in arid regions in western North America.
Gnetum consists of fewer than three dozen species, mainly large woody climbers (two are trees). Ten species occur in tropical South America, one in West Africa, and the remainder in tropical and subtropical Asia. The seeds and foliage of some species are eaten by humans.
Welwitschia includes just a single species, Welwitschia mirabilis, which is found in the Namib Desert of southwestern Africa (Namibia and Angola). The species is dioecious (i.e., individual plants are either male or female) and each adult plant consists of a giant taproot, a very short woody stem, and two permanent strap-shaped' leaves.
(Won and Renner 2006; McCoy et al. 2008; Zhong et al. 2010; Loera and Ickert-Bond 2012 and references therein)
- Loera, V. and S.M.Ickert-Bond. 2012. Diversification in North American arid lands: Niche conservatism, divergence and expansion of habitat explain speciation in the genus Ephedra. Molecular Phylogenetics and Evolution 65(2): 437-450.
- McCoy, S.R., J.V. Kuehl, J.L. Boore, and L.A. Raubeson. 2008. The complete plastid genome sequence of Welwitschia mirabilis: an unusually compact plastome with accelerated divergence rates. BMC Evolutionary Biology 8: 130.
- Won, H. and S.S. Renner. 2006. Dating dispersal and radiation in the gymnosperm Gnetum (Gnetales) - Clock calibration when outgroup relationships are uncertain. Systematic Biology 55(4): 610-622.
- Zhong, B., T. Yonezawa,Y. Zhong, and M. Hasegawa. 2010. The Position of Gnetales among Seed Plants: Overcoming Pitfalls of Chloroplast Phylogenomics. Molecular Biology and Evolution 27(12): 2855-2863.