On the Megagametophytes of Two Lepidodendracean Cones

Lepidodendracean fructifications with well-preserved megagametophytes are described from Pennsylvanian petrifactions of eastern Kentucky. One cone is megasporangiate with one functional alate spore in each sporangium; the other cone is bisporangiate with spinose megaspores and papillate microspores. Both strobili have megaspores that contain prothallia with rhizoids and well-developed archegonia. Ontogenetic stages of megagametophytic development in these cones are comparable to stages that occur in extant heterosporous lycopods. This study provides further evidence of a close phylogenetic relationship between the lepidodendrids and the extant genus Isoetes.