Molecular phylogenetic reconstructions of the marchantioid liverwort radiation

Molecular phylogenies of the complex-thalloid liverworts (Marchantiales) we re reconstructed using independent nuclear and plastid data sets to explore relative age, relationships, and character evolution in this ancient group . The sample includes 10 carpocephalate taxa and 24 acarpocephalate taxa (e mphasizing Riccia) within Marchantiales sensu stricto. In addition, Monocle a, Sphaerocarpos, Riella, three Metzgeriales (Fossombronia, Pellia, and Bla sia), the hornwort Anthoceros, four mosses, and outgroup Coleochaete are al so sampled. Two nucleotide sequence alignments were used 1) partial nuclear -encoded Large Subunit rDNA (LSU rDNA) for all 48 taxa and 2) the plastid-e ncoded trnL-F region for the marchantioids and outgroup Blasia. Alignment-a mbiguous regions of each alignment were culled. A combined matrix consistin g of concatenated nuclear and plastid culled alignments was assembled for m archantioids and Blasia The two alignments were utilized in four analyses: 1) nuclear LSU rDNA for all taxa, 2) nuclear LSU rDNA for marchantioids + B lasia, 3) plastid trnL-F region for marchantioids plus Blasia and 4) combin ed nuclear and plastid data for marchantioids plus Blasia Selected pairwise comparisons reveal significant rate heterogeneity in the nuclear LSU rDNA data; metzgerioid liverworts, hornworts and primitive mosses evolve signifi cantly slower than other taxa relative to the outgroup Coleochaete. The LSU rDNA genes of some marchantioid taxa and sampled bryalean mosses are appar ently evolving relatively fast. Rate heterogeneity is also documented withi n Marchantiales. Lunularia positions as the most basal of sampled Marchanti opsida; Sphaerocarpales, Marchantia, and Corsinia represent early diverging lines. A monophyletic Aytoniaceae, Cleveaceae, and Riccia are indicated. T opologies imply that extant acarpocephalate taxa are derived from carpoceph alate forms. Monoclea positions well within Marchantiales sensu stricto. A well-supported long branch (Decay Index = 19) unites all sampled Marchantio psida and isolates this clade from other liverworts and bryophytes. This lo ng branch may suggest extensive extinction of proto- and eomarchantioid for ms that led to modern taxa. A recurring theme in the topologies presented h ere is the unresolved marchantioid polytomy that follows well-supported bas al nodes. A similar polytomy results from either independent data set and m ay correspond to a rapid radiation of marchantioid forms (e.g., Aytoniaceae , Cleveaceae, Targionia, Monoclea, and riccioids) coincident with extreme c onditions and ecological reorganizations of the Permo-Triassic. The origin of Marchantiopsida probably occurred long before; amidst, perhaps, a series of long-extinct Blasia-like ancestors that colonized and innovated on any of various xeric surfaces (either cool or warm) that were available through out embryophyte history in the Paleozoic.