15.—Calathopteris heterophyllagen. et sp. nov., a Lower Carboniferous Pteridosperm bearing Two Kinds of Petioles

Abstract

Synopsis: Calathopteris heterophyllagen. et sp. nov. is described from a single petrified stem found in a loose block at Oxroad Bay, East Lothian. It is approximately 17 cm long and 2 cm diameter, being clothed with the swollen bases of incomplete petioles, many reflexed, and arranged in a dense 2/5 phyllotactic spiral. In most petioles the vascular bundle becomes U-shaped in transverse section with six abaxial mesarch lobes. Other leaf-traces divide in the inner cortex to form three concentric xylem strands which differentiate as they pass outward to form a median triarch bundle flanked by two tetrarch bundles. The stem possesses a medullated stele in which short wide tracheids occur in the medulla. Similarities between the petioles and those ofCalathospermum fimbriatumBarnard are pointed out while those with three bundles were probably trichotomous (and ?microsporangiate) likeDiplopteridium teilianumWalton.