Gillespiea randolphensis gen. et sp.nov. (Stauropteridales), from the Upper Devonian of West Virginia

Abstract

Numerous compression – limonitized specimens of small, delicate branch systems have been discovered in the Upper Devonian Hampshire Formation near Elkins, West Virginia. The fossils are described as Gillespiea randolphensis gen. et sp.nov., and assigned to the Stauropteridales. Axes are smooth and slender, range from less than 0.1 to 1.1 mm wide, and display quadriseriate branching. The largest axes of each system bear alternating pairs of smaller lateral axes, and this pattern is repeated in all but the smallest orders of branching. All axes are protostelic, consisting of a solid xylem core with marginally mesarch protoxylem strands, a narrow zone of putative phloem, and cortex. In transverse sections, steles of larger axes are three-to four-angled and have one to three protoxylem strands at each angle. Steles of the smaller axes are elliptical or round in cross section. Small, bifurcating lateral axes that bear sporangia are attached at the levels of branching and terminate the larger systems. Megasporangia are approximately 0.6 mm long and 0.3 mm wide, and contain one or two radial, trilete megaspores. Microsporangia have not been identified. This species extends the stratigraphic range of the Stauropteridales from the Carboniferous back to the Upper Devonian and demonstrates that the group had attained the grade of extreme heterospory by the Famennian.