Morphological and molecular systematic study of Chondracanthus (Gigartinaceae, Rhodophyta) from Pacific North America

Species boundaries in the Gigartinaceae are poorly defined due to the high degree of phenotypic plasticity exhibited by the thallus, with the result that many superfluous taxa have been described. To clarify the taxonomy of species of Chondracanthus Kutzing reported from the Gulf of California and Pacific coast of North America, morphological and molecular phylogenetic studies were performed. Phylogenetic analyses of chloroplast and nuclear DNA yielded nearly congruent hypotheses. DNA from type material was examined from select species to validate the correspondence between modern and historically important collections. Monographic observations on species from Pacific North America were included to clarify species boundaries. Analyses identified two species from the Gulf of California and nine from the Pacific coast. The following statements are supported: (1) Gigartina serrata Gardner is independent of Chondracanthus canaliculatus (Harvey) Guiry, and Chondracanthus serratus (Gardner) comb. nov. ...