Morphogenesis, developmental anatomy and bryophyte phylogenetics: contraindications of monophyly

Abstract

Three case studies are presented to prove that different ontogenetic patterns can produce similar morphologies. In Case I, it is shown that differences in leaf insertion and branch ontogeny between frullanioid and lejeuneoid lines are correlated with distinctive sequences of division in the apical derivatives. Case II demonstrates that the progression to distichy involves different mechanisms in mosses and liverworts. That Takakia is uniquely different from all other extant bryophytes and possesses a generalized meristem, rather than an apical cell system, is proven in Case III. Developmental similarities between Takakia and certain primitive tracheophytes are noted, and the division Takakiophyta is established for this truly phylogenetically isolated archegoniate. A coupling of palaeobotanical data about Silurian/Devonian terrestrial floras with the morphogenetic divergences that exist between liverworts, hornworts, mosses, takakiophytes and tracheophytes are seen to support a polyphyletic origin of archegoniates.