Biogeography and systematics of Bangia (Bangiales, Rhodophyta) based on the Rubisco spacer, rbcL gene and 18S rRNA gene sequences and morphometric analyses. 1. North America

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Marine and freshwater populations of the red alga Bangia were sampled throughout most of the known geographic range in North America. Marine samples were obtained from the Pacific and Atlantic coasts, central Arctic, Gulf of Mexico, and the Virgin Islands. Freshwater samples came from populations in the Laurentian Great Lakes, St. Lawrence River, and Lake Simcoe. In addition, specimens from freshwater populations from Italy, England, and Ireland were included for comparison. DNA sequence analyses of the Rubisco spacer, rbcL gene, and 18S rRNA gene, plus morphometric analysis, were used to discern possible biogeographic and taxonomic trends. No correlation was detected between the molecular and morphological analyses; however, some trends were consistent among the three molecular analyses. For example, all the freshwater collections were nearly identical, indicating that a single lineage may exist in freshwater systems. In addition, the Virgin Islands sample was distinct from all others in both the rbcL and 18S rRNA gene sequences, but quite similar in morphology to those collections with small filament diameter. The Alaska sample clustered consistently with a primarily Atlantic clade with few sequence differences. This finding may indicate a transarctic invasion. Sequence analysis of the 18S rRNA gene yielded a previously unreported intron (in Bangia) located between helices 21 and 20′. All freshwater collections contained this intron, but it was present only in some marine collections. Considerable sequence divergence occurred among groups of collections in both the rbcL (0–16%) and 18S rRNA (0–10.6%) genes with little corresponding diversity in morphology. These values are higher than those reported previously for intergeneric, intrafamilial, or interfamilial comparisons in higher red algal taxa, but are consistent with those reported for the members of the Bangiales. Sequence analysis of the 18S rRNA gene of Bangia collections with six Porphyra species yielded a tree in which Porphyra is paraphyletic within Bangia. In addition, the molecular divergence appears to be quite low between the two genera.