Phylogeny of the genus Coleochaete (Coleochaetales, Charophyta) and related taxa inferred by analysis of the chloroplast gene rbcL

The genus Coleochaete Breb. is considered to be a key taxon in the evolution of green algae and embryophytes (land plants), but only a few of the approximately 15 species have been studied with molecular phylogenetic methods. We report here the sequences of the gene rbcL from six new cultures of Coleochaete and two of Chaetosphaeridium Klebahn. These sequences were combined with 32 additional sequences, and phylogenetic analyses were performed with maximum likelihood, distance optimality, and parsimony methods. Important subgroups within Coleochaete include two primary lineages, one marked toy fully corticated zygotes and the other by naked or weakly corticated zygotes. In the first lineage there is a subclade with tightly joined filaments and distinctive ("T-shaped") cell division, an assemblage of strains that resembles the endophytic species Coleochaete nitellarum Jost, and a clade with loosely joined ilaments and "Y-shaped" cell divisions. Consistent with recent multigene phylogenies, these analyses support the monophyly of the Coleochaetales, place the Charales as the sister taxon to land plants, and indicate that Chaetosphaeridium is far more closely related to Coleochaete than to Mesostigma Lauterborn.