Systematics of Ulvaceae (Ulvales, Ulvophyceae) and the genus Ulva L. based on nuclear and chloroplast sequence data
Systematic hypotheses for Ulvaceae were tested using sequences for the chloroplast gene encoding the large subunit of RUBISCO (rbc L) and nuclear small subunit ribosomal DNA (18S rDNA). Ulvaceae sensu Floyd and O'Kelly (1990), including Percursaria, Ulvaria and a complex of closely related species of Chloropelta, Enteromorpha and Ulva, is supported. Morphological synapomorphies for the family include the early development of vegetative thalli and motile cell ultrastructure. Method of flagellate release and gross morphology are not systematically reliable characters. The Ulvales and Ulotrichales sensu Floyd and O'Kelly (1990) are monophyletic. Blidingia and Kornmannia are allied with the former and Capsosiphon with the latter, though relationships among these and other taxa in these orders remain uncertain.Sequences of the internal transcribed spacers of nuclear ribosomal DNA (ITS nrDNA) and rbcL were analyzed to test the monophyly of the cosmopolitan genera Ulva and Enteromorpha . Phylogenetic analyses indicate that neither Ulva nor Enteromorpha are monophyletic; however, with the exception of Ulva olivascens, all sampled Ulva and Enteromorpha form a strongly supported clade. Within this clade, there are smaller clades comprised of all distromatic, all tubular, and both distromatic and tubular species; however, few morphological synapomorphies defining these clades can be identified, given the simple morphology and high degree of phenotypic plasitcity in these algae.A phylogeny of Ulva and Enteromorpha in the northeast Pacific was reconstructed to test existing species hypotheses. ITS nrDNA and rbcL sequences were determined for accessions from the northeast Pacific, Australia, Chile, Hawaii and Japan and were combined with existing sequences for European taxa, for analysis. Species were inferred based on monophyly of sampled sequences, and secondarily, sequence divergence. Three species of Enteromorpha and seven species of Ulva are inferred to occur in this region: E. intestinalis, E. linza, E. prolifera, U. californica, U. lactuca, U. lobata, U. pseudocurvata, U. rigida, U. stenophylla and U. taeniata. Three of these appear to be polyphyletic: E. linza, E. prolifera and U. taeniata. The presence of an eighth species, U. rotundata, is uncertain. The monospecific genus Chloropelta is nested among Ulva and Enteromorpha species. Chloropelta caespitosa is recognized as Ulva caespitosa.
- Biology