TRANSITION TO A LAND FLORA: PHYLOGENETIC RELATIONSHIPS OF THE GREEN ALGAE AND BRYOPHYTES

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Abstract
— Separate cladistic analyses of the green algae, liverworts, and hornworts are presented. Classificatory and evolutionary implications of these analyses, in addition to our previously published cladistic analyses of mosses and the embryophytes as a whole, are discussed. The embryophytes are monophyletic, and are part of a larger monophyletic group that includes some of the green algae (the “charophytes”). Important evolutionary transformations in the early phylogeny of the land plants include: (1) retention of the zygote on the haploid plant (gametophyte), with the sporophyte generation arising de novo by delaying meiosis, (2) independent elaboration of an elongate sporophyte in some liverworts, some hornworts, and in the moss-tracheophyte clade, (3) independent origin of radial (axial) symmetry in the gametophyte in some liverworts and in the moss-tracheophyte clade, (4) independent origin of leaves on the gametophyte in some liverworts and in mosses, and (5) the unique development of a branching sporophyte with multiple sporangia in the tracheophytes.