Systematics of Grateloupia filicina (Halymeniaceae, Rhodophyta), based on rbcL sequence analyses and morphological evidence, including the reinstatement of G-minima and the description of G-capensis sp nov.

Grateloupia filicina (C. Agardh) Lamouroux, originally described from the Mediterranean Sea, has long been considered a textbook example of a marine red alga with a cosmopolitan distribution. An rbcL-based molecular phylogeny, encompassing samples covering the entire geographic distribution of the species, revealed a plethora of cryptic species, whereby the presence of genuine G. filicina is limited to the Mediterranean basin. The phylogeny revealed a strong biogeographic imprint, with specimens from temperate regions resolved in clades composed of species inhabiting the same geographic region. Presence of widely divergent morphologies in the temperate clades indicated that several lineages have converged independently to a G. filicina-type morphology. Tropical representatives are resolved in a single clade with very uniform G. filicina-type morphology and pairwise sequence divergences that are lower than the average divergence observed in temperate lineages. This, combined with a lack of clear geographic structure among the tropical lineages, may indicate a more recent divergence with long-range dispersal capacities. Violations to the biogeographic signal in temperate lineages seemed to be due to either inadequate taxonomy or recent introductions. Grateloupia minima P. G H. Crouan, a taxon placed in synonymy under G. filicina, is reinstated as a separate species distributed in the northeast Atlantic Ocean. Grateloupia capensis sp. nov. is described to accommodate specimens from South Africa with a G. filicina-type morphology, and G. filicina var. luxurians is elevated to species status. Morphological and anatomical characters were put forward that support the distinctiveness of these three distinct species.