Systematics of the gracilariaceae (Gracilariales, rhodophyta):: A critical assessment based on rbcL sequence analyses

Generic concepts in the economically important agarophyte red algal family Gracilariaceae were evaluated based on maximum parsimony, Bayesian likelihood, and minimum evolution analyses of the chloroplast-encoded rbcL gene from 67 specimens worldwide. The results confirm the monophyly of the family and identify three large clades, one of which corresponds to the ancestral antiboreal genera Curdiea and Melanthalia, one to Gracilariopsis, and one to Gracilaria sensu lato, which contains nine distinct independent evolutionary lineages, including Hydropuntia. The species currently attributed to Hydropuntia comprise a single well-supported clade composed of two distinct lineages. The two most basal clades within Gracilaria sensu lato deserve generic rank: a new genus centered around G. chilensis Bird, McLachlan et Oliveira and G. aff. tenuistipitata Chang et Xia and a resurrected Hydropuntia encompassing primarily Indo-Pacific (G. urvillei [Montagne] Abbott, G. edulis [S. Gmelin] P. Silva, G. eucheumatoides Harvey, G. preissiana [Sonder] Womersley, and G. rangiferina [Kutzing] Piccone) and western Atlantic species (G. cornea J. Agardh, G. crassissima P. et H. Crouan in Maze et Schramm, G. usneoides [C. Agardh] J. Agardh, G. caudata J. Agardh, and G. secunda P. et H. Crouan in Maze et Schramm). Cystocarpic features within the Gracilaria sensu lato clades appear to be more phylogenetically informative than male characters. The textorii-type spermatangial configuration is represented in two distinct clusters of Gracilaria. The rbcL genetic divergence among the Gracilariaceae genera ranged between 8.46% and 16.41%, providing at least 2.5 times more genetic variation than does the 18S nuclear rDNA. rbcL also resolves intrageneric relationships, especially within Gracilaria sensu lato. The current number of gracilariacean species is underestimated in the western Atlantic because of convergence in habit and apparent homoplasy in vegetative and reproductive anatomy.