An arborescent lycopsid from the Lower Carboniferous Price Formation, southwestern Virginia, USA and the problem of species delimitation

A large assemblage of stems, leaves and reproductive structures collected from a single horizon in the Lower Mississippian (Lower Carboniferous) Price Formation of southwestern Virginia, USA is recognized as representing the components of a distinctive arborescent lycopsid. While similar forms previously were included in Lepidodendropsis Lutz, an eligulate lycopsid in which leaf scars are not apparent, these specimens document the presence of both well-defined leaf scars and ligules. Among larger specimens, leaf base patterns change along the length of a single stem, each morphology conforming to a different species of Lepidodendropsis. Because of the overlapping variability within specimens, we find that stems of different sizes and leaf base patterns are parts of the same plant. This plant was a tree with a trunk that probably attached to a cormose base previously recognized as Protostigmaria Jennings. The trunk extended 3-4. m before branching dichotomously to produce a crown of several orders of branches, with the distal-most ones still bearing long tapering leaves. Sporangia are borne in fertile zones; the plant is heterosporous. The presence of leaf scars and a ligule (features explicitly lacking in the generic diagnosis of Lepidodendropsis) as well as other plant organs for this taxon precludes inclusion in Lepidodendropsis; rather, this plant should be placed in a new genus. A better understanding of this plant, and other specimens attributed to Lepidodendropsis, may aid in elucidating transitions and phylogenetic relationships among Late Devonian-Late Carboniferous arborescent lycopsids.