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The Enigmatic Paleozoic plants Spermopteris and Phasmatocycas reconsidered¹

²Department of Biological Sciences, LSCB 124, University of South Alabama, Mobile, Alabama 36688 USA; ³Division of Paleobotany, Natural History Museum and Biodiversity Research Center, Lawrence, Kansas 66045 USA; ⁴Bayerische Staatssammlung für Paläontologie und Geologie, Funktionseinheit Paläontologie, Richard-Wagner-Straße 10, 80333 Munich, Germany; ⁵Department of Ecology and Evolutionary Biology and Natural History Museum and Biodiversity Center, University of Kansas, Lawrence, Kansas 66045 USA; ⁶Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 205609 USA

Ovule-bearing leaves from the Paleozoic of North America assigned to Spermopteris and Phasmatocycas have been interpreted as primitive cycad megasporophylls. According to this hypothesis, Cycas megasporophylls were derived from a Spermopteris-like ancestor via Phasmatocycas and various other taeniopterid forms. This putative transformation entailed the phyletic shift of ovule attachment from the abaxial lamina surface of Spermopteris to the leaf midrib in Phasmatocyas. However, reexamination of the original Spermopteris specimens from the Lawrence Shale of Kansas has shown that the ovules are attached to the leaf midrib. Therefore, Spermopteris and Phasmatocyas differ only in a few details of lamina morphology. The apical cleft of the ovules of both forms is interpreted as an original feature rather than a preservational artifact; however, the abaxial flange is probably a result of compression of a terete midrib. Spermopteris is typified by sterile specimens of Taeniopteris coriacea from Europe, which are of uncertain affinity to the fertile leaves. Therefore, we propose that the ovule-bearing leaves now known as Spermopteris coriacea be named as a new species of Phasmatocycas (Phasmatocycas bridwellii sp. nov.). The new concept of Phasmatocyas is less cycad-like than previously thought, and the phylogenetic position of the genus is unclear.

Key Words: Carboniferous • cycads • Permian • Phasmatocyas • pteridosperms • Spermopteris • Taeniopteris

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