A NEW GENUS OF GIGANTOPTERID FROM THE MIDDLE PERMIAN OF THE UNITED STATES AND CHINA AND ITS RELEVANCE TO THE GIGANTOPTERID CONCEPT

摘要

The gigantopterids are a poorly understood group of plants defined primarily on the basis of a particular type of reticulate leaf venation in combination with stratigraphic distribution. It is generally agreed that many, if not all, are seed plants. A new genus of gigantopterid, Euparyphoselis gen. nov., is described from foliage only, derived from the Middle Permian of the southwestern United States and eastern China. One species occurs in each area: Euparyphoselis gibsonii sp. nov. in the United States and Euparyphoselis marginervum (Yao and Liu) comb. nov. in China. The most significant characteristic of the new genus is a marginal vein. The foliage displays three and occasionally four orders of venation, with a variably distinct suture vein between second-order veins, formed by the fusion of tertiary veins from adjacent secondaries. The leaves are obovate in shape and unforked, tapering toward the base. Leaf margins are smooth or bluntly toothed with broad, shallow sinuses between the teeth. Secondary veins end or dissipate into the teeth, where present. Leaves are amphistomatic; stomatal complexes are haplocheilic and monocyclic. The two species differ mainly in the characteristics of the epidermal surfaces, including the shape and size of the epidermal and subsidiary cells, stomatal complexes, number of subsidiary cells, orientation of the stomatal complexes, and secretory structures. Euparyphoselis marginervum was originally described as a species of Gigantopteridium, with which it shares certain characteristics of venation. However, it clearly differs from Gigantopteridium in the details of venation and in leaf architecture. It is argued that leaf venation should not be given primacy over all other characteristics when assessing gigantopterid relationships and therefore as a basis for taxonomy. As previously suggested, the gigantopterids, as presently construed, may not be a monophyletic group.