A molecular approach to investigate the phylogenetic basis of three widely used species groups in the red algal genus Ceramium (Ceramiales, Rhodophyta)

摘要

The taxonomy of Ceramium (Ceramiales, Rhodophyta) is difficult because of large and complex morphological variation. Three species groups are often recognised; one group that can develop fully corticated internodes, one group with ecorticate internodes, and one group with cortical spines. Two different molecular markers (the plastid rubisco spacer and one part of the large subunit [LSU] of nuclear ribosomal DNA) were used to investigate whether the three species groups have a phylogenetic basis. Sequence analyses of 15–17 North Atlantic species of Ceramium revealed highly conserved partial LSU sequences, whereas the rubisco spacer region was variable among, as well as within several species. Analyses of the rubisco spacer sequences, and in particular the combined data set, produced fairly resolved phylogenies with several well-supported relationships that were highly incongruent with the informal species groups. These results suggest that cortical spines and internode cortication have evolved several times in Ceramium.