a color plate from the essay
The Origin and Early Diversification of Angiosperms
by Peter R. Crane, Else Marie Friis and Kaj Raunsgaard Pedersen
Figure 5 (from page 246 of Shaking the Tree: Readings from Nature in the History of Life edited by Henry Gee)
Gnetales consist of only three extant genera: Ephedra (a, about 40 species in arid and semiarid areas); Welwitschia mirabilis (b, one species restricted to the Namibian Desert); and Gnetum (c, about 30 species of tropical rainforest lianas and small trees). Despite the obvious morphological differences the group is widely regarded as monophyletic (Box 1) and is united by multiple axillary buds, opposite/decussate phyllotaxis (also reflected in the reproductive structures), circular bordered pits in the protoxylem, vessels (?derived independently to those in angiosperms) and a feeder in the embryo.10,11 In addition, Welwitschia and Gnetum share several derived characters that are thought to be convergent with similar features in angiosperms10,11 (see Box 1).
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About the book: Shaking the Tree: Readings from Nature in the History of Life edited by Henry Gee, published by the University of Chicago Press.