Anatomy and frond architecture of Neuropteris ovata and N. scheuchzeri from the Upper Pennsylvanian of the Appalachian Basin

Abstract

Two medullosan fronds have been reconstructed from permineralized fragments collected at one late Pennsylvanian outcrop in the Appalachian Basin. Fragments are assignable to Myeloxylon, Neuropteris ovata, N. scheuchzeri, Mixoneura, and Cyclopteris and attached stems correspond to Medullosa noei. The fronds are pinnately compound. Branching patterns, anatomical features, and size ranges intergrade from the largest to the smallest axes. Thin areas in the hypodermal sclerenchyma zone on the adaxial sides of rachises and primary pinnae are sites of attachment of intercalary vascularized emergences. Vascularized emergences and tertiary pinnae are identical in configuration: they have five–seven vascular bundles and are about 2 mm in diameter. Neuropteris ovata pinna rachises and N. scheuchzeri petiolules are similar in size and vascular configuration to vascularized emergences and tertiary pinnae. Mixoneura pinna rachises are identical to axes sometimes found attached to Neuropteris ovata pinna rachises. The differences in the epidermal features of N. ovata and N. scheuchzeri pinnules support the conclusion that they represent two distinct species. Proximal frond members are identical in anatomy and general architecture.