The microspores of Pleuromeia rossica Neuburg (Lycopsida; Triassic):: comparative ultrastructure and phylogenetic implications

The ultrastructural features of the microspores of the Triassic lycopsid Pleuromeia rossica are similar to those of the microspores of the living Isoetes, except that the latter have an additional outermost wall. These features differ greatly from those of the spores of all the other extant Pteridophyta. Likewise, the megaspores of P. rossica, of which the comparative analysis will be presented later, are also ultrastructurally analogous to the megaspores of Isoetes. These ultrastructural similarities very likely imply close relationships between Pleuromeia and Isoetes. Moreover they suggest that these genera belong to a distinct group among the heterosporous lycopsids, in which the ultrastructural features of the microspores remained outstandingly steady. ((C) 1999 Academie des sciences / Editions scientifiques et medicates Elsevier SAS.).