Biogeography and systematics of Hildenbrandia (Rhodophyta, Hildenbrandiales) in Europe: inferences from morphometrics and rbcL and 18S rRNA gene sequence analyses

Twenty-one marine and freshwater specimens of Hildenbrandia from Europe wer e compared by analyses of morphometric data and sequences of the rbcL chlor oplast gene (which codes for the large subunit of the ribulose-1,5-bisphosp hate carboxylase/oxygenase enzyme) and the nuclear 18S ribosomal RNA (rRNA) gene. Eleven freshwater specimens, all corresponding to H. ribularis, were collected from the British Isles, Germany, France, Austria Spain and Italy . Six marine specimens, representing H. rubra, were obtained from Northern Ireland, Wales, France, Norway, Sweden and the Netherlands, while four mari ne specimens, corresponding to H. crouanii, were collected from Scotland an d Germany. Morphometric analyses of vegetative and reproductive characters distinguished three groups of specimens, which correspond to the three spec ies. Parsimony and distance analyses of the rbcL and 18S rRNA genes were pe rformed on these samples and sequences of North American representatives we re included to determine their inter-relationships. The rbcL gene sequence analyses separated the marine and freshwater specimens, with the H. rivular is and H. angolensis representatives forming a well-supported monophyletic clade. The rbcL sequence analyses did not resolve the groupings of marine s pecimens determined in the morphometric analysis. Analyses of the 18S rRNA gene sequences also supported separation of the marine samples from freshwa ter samples, although the bootstrap and decay support was not as strong as for the rbcL gene. H. rubra formed a monophyletic clade that was weakly sup ported. In terms of biogeographic trends, the fairly low intraspeci8e diver gence of H. rivularis (0-1.9% for the rbcL gene and 0-3.6% for the 18S rRNA gene) and the positioning of these samples in the gene trees supports the concept that they are derived from marine populations.