This research promotes the correlation of molecular phylogenies and morphological data with biogeographic hypotheses for the economically important agarophyte family Gracilariaceae. The generic concepts are evaluated on the basis of chloroplast-encoded rbcL sequences from 150+ specimens worldwide. The results confirm the monophyly of the family and identifies 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 identifies at least nine distinct independent evolutionary lineages, including Hydropuntia. The species currently attributed to Hydropuntia comprise two well-supported clades with different biogeographic patterns, one composed of Indo-Pacific species and the other of Atlantic species. At least the three most basal clades within Gracilaria sensu lato deserve to be considered distinct genera: 1) a new genus centered around G. chilensis and G. tenuistipitata; 2) Hydropuntia sensu stricto encompassing Pacific species (G. urvilleii, G. eucheumatoides, G. edulis), and 3) a new genus composed of Atlantic species currently placed in Hydropuntia (G. cornea, G. crassissima, G. usneoides). Cystocarp features within the Gracilaria senso lato clades are more phylogenetically informative than do male characters. The henriquesiana-type of spermatangial concepacle appeared independently at least 4 times. The textorii-type of male apparatus is represented in two distinct clusters of Gracilaria. Several unknown and poorly described species are being described, resurrected from synonymy or recircunscribed. G. textorii seems to be part of a major complex of flat species in the Pacific Ocean. The current number of Gracilariaceae is underestimated in the Western Atlantic due to convergence in habit type and the apparent homoplasy in vegetative and reproductive anatomy.

Key words: agar, algae, Gracilariaceae, phylogeny, rbcL, Rhodophyta