Abstract
Despite substantial evolutionary interest in the order Gnetales as the extant group of seed plants most similar to the angiosperms, our knowledge of systematic relationships within the genera of the group remains quite limited. The most recent worldwide monograph of Ephedra is that of Stapf (1889), while the only worldwide systematic treatment of Gnetum is that of Markgraf (1930). This article summarizes our current knowledge of the relationships among the ca. 50 species of Ephedra and the ca 39 species of Gnetum and the relationships between these two genera and the monotypic Welwitschia. Preliminary phylogenetic analyses of rbcL gene sequences, including three species each of Ephedra and Gnetum, provide further support for the monophyly of the Gnetales relative to the other extant groups of seed plants and for the sister-group relationship of Ephedra and Gnetum.
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