Molecular and morphological analyses of Bryopsis (Bryopsidales, Chlorophyta) from the western North Atlantic and Caribbean

Three species of Bryopsis have commonly been reported from the western Nort h Atlantic, but continuous morphological variation has often confounded spe cimen identification. This study evaluates the utility of the coding and no n-coding sequences of the psbB gene cluster of Bryopsis. compared to morpho logical characters, as a means of distinguishing Bryopsis species. The sequ ences examined include a group Il intron within the psbT gene, the 3' exon of this gene, the spacer separating psbT and psbH, as well as the 5' part o f the latter gene. Sequences of 616 bp of Bryopsis from 28 collections from the study area were aligned with those for eight collections from elsewher e in the Atlantic and Pacific. in order to test the monophyly of Atlantic B ryopsis. The phylogenies were rooted using Lambia as an outgroup. Parsimony analysis resolved the sequences into five clades. with strong bootstrap su pport. Three of the clades had wide distributions. two including individual s from both the western and eastern North Atlantic and the Pacific and one including plants from the Caribbean and the Pacific. The other two clades w ere more restricted: one clade was found only in the warm temperate western North Atlantic. and the other derived from the central California coast. T hree methods of cluster analysis were applied to the morphological data but failed to find robust higher level structure; they neither supported nor r efuted the molecular data. The four clades from the western North Atlantic and Caribbean appear to be either seasonally or geographically disjunct thr oughout this region. The molecular data support the current recognition of multiple species of Bryopsis along the western North Atlantic, some with wo rldwide distributions, but the morphological data do not correlate with thi s.