Rhacophyton from the Upper Devonian of West Virginia

Abstract

A new species of Rhacophyton, R. ceratangium, is described from Upper Devonian rocks of West Virginia, U.S.A.; this is synonymous with R. incertum (Dawson) Krausel and Weyland but reasons are cited to indicate that the latter species name is not appropriate. The collections include: stems up to 2 cm in diameter bearing bipinnate, non-laminate vegetative fronds; abundant well preserved fertile fronds that show clearly the distinctive morphology of their sterile and fertile pinnae; fragments of axes with woody tissues petrified. The sporangia are particularly distinctive with their long slender tip; they dehisced longitudinally and contained several hundred spores; all available evidence indicates that the plant was homosporous. All petrified axes have a slender bar-shaped strand of primary wood swollen at either end and surrounded by strongly developed secondary wood consisting of scalariform tracheids and rays. R. ceratangium is closely related to the Belgian R. zygopteroides Leelercq. A comparison with other Devonian and Carboniferous pteridophytes suggests that Rhacophyton is probably a primitive member of the Progymnospermopsida or immediately ancestral to that group.