Department of Biological Sciences, LSCB 124, University of South Alabama, Mobile, Alabama 36688 USA;
Am J Bot. 2003 Nov;90(11):1585-95. doi: 10.3732/ajb.90.11.1585.
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.
来自北美的古生代具胚珠的叶子被分配给鳞木属和拟大羽羊齿属，被解释为原始苏铁大孢子叶。根据这一假说，苏铁大孢子叶是通过拟大羽羊齿属和其他各种 taeniopterid 形式从鳞木属的祖先中衍生而来的。这种假定的转变涉及到胚珠附着从鳞木属的背腹面叶表皮转移到拟大羽羊齿属的叶片中脉。然而，对堪萨斯州劳伦斯页岩中原始鳞木属标本的重新检查表明，胚珠附着在叶片中脉上。因此，鳞木属和拟大羽羊齿属仅在叶片形态的几个细节上有所不同。这两种形式的胚珠的顶端裂隙被解释为原始特征，而不是保存上的假象；然而，背面的翅可能是圆形中脉压缩的结果。鳞木属的典型特征是来自欧洲的 Taeniopteris coriacea 的不育标本，它们与可育叶的亲缘关系不确定。因此，我们建议将现在称为鳞木属 coriacea 的具胚珠的叶子命名为拟大羽羊齿属的一个新种（Phasmatocycas bridwellii sp. nov.）。拟大羽羊齿属的新概念比以前认为的更不具有苏铁特征，而且该属的系统发育位置尚不清楚。
