The phylogenetic history of and evolutionary trends within the simple thalloid liverworts (Jungermanniopsida, subclass Metzgeriidae) are reconstructed in a combined analysis of molecular and morphological data. The molecular dataset comprises loci from all three genomes, including trnL-F, rps4, rbcL, atp and psbA from the chloroplast, SSU rRNA and LSU rRNA from the nucleus, and nad5 from the mitochondrion, and 65 characters are scored in the morphological dataset. An initial analysis of a molecular dataset that included 16 outgroup and 50 ingroup taxa resolved a Haplomitrium/Treubiaceae clade as the earliest diverging lineage of the ingroup. Subsequent analyses of ingroup only datasets, rooted on this clade, resolve Metzgeriidae as paraphyletic, with Blasiaceae sister to Marchantiopsida in all analyses. A combined analysis of morphological and molecular datasets resolves basically the same clades as analyses of the molecular dataset alone, except for the resolution of a weak sister group relationship between Metzgeriineae and the leafy liverworts. Reconstructions of morphological character evolution on the combined analysis topology confirm that there is substantial homoplasy in the morphology dataset, even in characters that have been traditionally considered diagnostic of hierarchial relationships, such as apical cell geometry, calyptral type and capsule wall thickness. Ancestral state reconstructions contradict many prevailing hypotheses of character evolution in hepatics, including the model of the ancestral liverwort prototype as an erect, radially symmetric plant. Instead, a more likely model is a prostrate, bilaterally symmetric plant with the diagnostic features of a simple thalloid liverwort.
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