Polarity of peatmoss (Sphagnum) evolution: who says mosses have no roots?

DNA sequences from 16 genomic regions representing the mitochondrial, chloroplast, and nuclear genomes (ca. 16 KB) were obtained from 24 species of Sphagnum plus one species each from Takakia and Andreaea. Two to four species represented each section of the genus (based on previous analyses). The analyses were conducted in a two-step fashion because variable regions of the genome, necessary to resolve relationships among sections within Sphagnum, could not be aligned with those from the outgroups, and more conserved regions were too-little variable within Sphagnum. Analyses based on the 8 conserved regions resolved two species, S. sericeum and S. lapazense, as sister to the rest of the genus (Fig. 1).

Subsequent analyses including all available sequence data (15 loci) were rooted to S. lapazense and S. sericeum and Takakia/Andreaea were deleted from the dataset. The main Sphagnum lineage consists of two clades; one includes the sections Sphagnum, Rigida, and Cuspidata, and the other includes Subsecunda, Acutifolia, and Squarrosa (Fig. 2). The placement of section Subsecunda is weakly supported, but other nodes are strongly supported by maximum parsimony, maximum likelihood, and Bayesian analyses.

In addition to homogeneous Bayesian analyses, heterogeneous models were employed to account for different patterns of nucleotide substitution among genomic regions. Critical morphological characters were reconstructed on this phylogeny using likelihood-based methods (implemented in MESQUITE; Maddison & Maddison 2003).

Reference:

Shaw, A. J., C. J. Cox, & S. B. Boles. 2003. Polarity of peatmoss (Sphagnum) evolution: who says mosses have no roots? American Journal of Botany 90: 1777-1787. reprint suppl.

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