DIAPHORODENDRACEAE, FAM-NOV (LYCOPSIDA, CARBONIFEROUS) - SYSTEMATICS AND EVOLUTIONARY RELATIONSHIPS OF DIAPHORODENDRON AND SYNCHYSIDENDRON, GEN-NOV

Synchysidendron, gen. nov., is segregated from Diaphorodendron DiMichele emend. Both genera are determinate, rhizomorphic, arborescent lycopsids that share identical reproductive organs but differ radically in growth architecture and consequently in the timing of reproduction. Cones in Synchysidendron (two species) are borne on late-formed crown branches; in Diaphorodendron (three species) cones are borne on deciduous lateral branches, produced over much of the life of the tree. The two genera also differ in several characteristics of the stele and periderm. We hypothesize that Diaphorodendron gave rise to Synchysidendron within their shared Late Carboniferous coal-swamp habitat, by heterochronic suppression of lateral branching during ontogeny. Together, these genera form a highly apomorphic clade, here recognized as the new family Diaphorodendraceae, that is distinguished primarily by siphonostelic axes, a bifacial periderm, distinctive megasporangia, and gulate megaspores.