Molecular evolution of the atpB-rbcL noncoding spacer of chloroplast DNA in the moss family Hylocomiaceae

Molecular evolution of the chloroplast noncoding region between the atpB and rbcL genes was investigated in the moss family Hylocomiaceae. Nucleotide substitution contributed to most of the variation among taxa, although an insertion of 29 base pairs was found in Rhytidiopsis robusta. The evolution of atpB-rbcL intergenic spacer was constrained in Hylocomiaceae compared to the evolutionary rates of this chloroplast spacer, and even of the rbcL gene, in angiosperms. Using a relative rate test procedure, substitution rates of the chloroplast spacer were found to be consistent with the hypothesis of a molecular clock, except for three taxa. Based on previous knowledge of the evolutionary rate of this spacer in true mosses, the divergence of the Hylocomiaceae from their common ancestor was estimated to be 29.0 million years ago, which is consistent with the fossil record. The chloroplast sequences supported the monophyly of the Hylocomiaceae with a bootstrap value of 82%. The effects of long branch attraction caused the erroneous placements of Rhytidiopsis and Rhytidium in the parsimony analysis. In contrast, neighbor-joining analysis provided a more congruent estimate of the phylogeny of the Hylocomiaceae based on the cpDNA variation observed.