The relationships of vascular plants

Recent phylogenetic research indicates that vascular plants evolved from br yophyte-like ancestors and that this involved extensive modifications to th e life cycle. These conclusions are supported by a range of systematic data , including gene sequences, as well as evidence from comparative morphology and the fossil record. Within vascular plants, there is compelling evidenc e for two major clades, which have been termed lycophytes (clubmosses) and euphyllophytes (seed plants, ferns, horsetails). The implications of recent phylogenetic work are discussed with reference to life cycle evolution and the interpretation of stratigraphic inconsistencies in the early fossil re cord of land plants. Life cycles are shown to have passed through an isomor phic phase in the early stages of vascular plant evolution. Thus, the gamet ophyte generation of all living vascular plants is the product of massive m orphological reduction. Phylogenetic research corroborates earlier suggesti ons of a major representational bias in the early fossil record. Megafossil s document a sequence of appearance of groups that is at odds with that pre dicted by cladogram topology. It is argued here that the pattern of appeara nce and diversification of plant megafossils owes more to changing geologic al conditions than to rapid biological diversification.