Megaspore morphology in the Selaginellaceae in a phylogenetic context: A study of the megaspore surface and wall structure using scanning electron microscopy

Megaspore morphology in the lycopod family Selaginellaceae is studied using scanning electron microscopy. The 52 species examined correspond to taxa included in a molecular phylogenetic analysis of the family, based on rbcL gene sequences, and represent the morphological and geographical variation found within the group. Surface sculpture and wall structure are described. A revised terminology to describe the continuum seen in wall structures is presented. The morphological variation is discussed in a phylogenetic context and several putative synapomorphies of clades within the family are identified. This study allows us to assign extant and fossil megaspores to monophyletic groups within the Selaginellaceae.