PHYLOGENY OF ATLANTIC SPECIES OF GRACILARIACEAE (RHODOPHYTA) BASED ON SMALL SUBUNIT RIBOSOMAL GENE SEQUENCING

The complete small subunit ribosomal nuclear gene (ssu rDNA) sequence was determined for nine species of Gracilaria and one species of Gracilariopsis which are common on the American Atlantic waters. The sequences were aligned using the secondary structure as reference, including the published sequences of nine other species of Gracilariaceae. A matrix of 1736 sites was constructed with a proportion of 91% invariable sites and very few assumed indels events. All the inferred trees show three main lineages: 1) the strongly divergent lineages of Gracilariopsis; 2) the austral genera Curdiea / Melanthalia; and 3) the lineage of Gracilaria sensu stricto. The later encompasses the following groups: 1) Gracilaria chilensis from the Pacific ocean; 2) a group of cylindrical tropical species with "henriquesiana" spermatangial type; 3) a group of warm temperate cylindrical species with "verrucosa" spermatangial type; and 4) a group of flattened tropical species with mainly "textorii" spermatangial type. The relationship of a species described as Gracilaria pauciramosa from Venezuela was not inequivocally solved. The inferred phylogenetic groups are congruent with morphology and quality of agar.