Lepidodendron hickii and Generic Delimitation in Carboniferous Lepidodendrid Lycopods

Abstract

hickii is the only anatomically preserved Carboniferous lepidodendrid with leaf cushions referable to the compression-based L. aculeatum, the type of Lepidodendron. His- torically has come to encompass several kinds of arborescent lycopods with distinc- tive vegetative and reproductive morphologies, among which no truly intermediate forms are known. These include totally or in part Lepidophloios (and Sublepidophloios, a possible congener), Paralycopodites, Lepidodendron sensu L. vasculare and others, and a large number of fragmentary specimens of varying affinities. The discrete nature of the character states defining these genera suggests that anatomy is sufficient for delimitation of lepidodendrid genera. Simple leaf-cushion shape is of dubious value in the delimitation of because the Lepidodendron-shape appears to be plesiomorphic (ancestral). hickii is associated with Achlamydocarpon takhtajanii megasporangium-sporophyll units, which suggests close alliance with the herbaceous L. serratum, also a producer of A. takhtajanii. At the generic level, (sensu L. hickii and L. serratum) is most similar phenetically to Lepidophloios.