Molecular and morphological characterization of Laurencia intricata and Laurenciella mayaimii sp. nov. (Ceramiales, Rhodophyta) in South Florida, USA

Morphological characterization, together with phylogenetic and DNA barcoding analyses on the basis of rbcL and COI-5P, conducted on some species of the Laurencia complex in South Florida confirmed the occurrence of Laurencia intricata and supported the presence and recognition of Laurenciella in the United States. Samples of L. intricata from Florida grouped with full support with the species from the type locality (Antilles). The intraspecific divergence within the L. intricata Glade ranged from 0.0% to 1.3%; the samples from Florida diverged by only 0.06% to 0.20%, the sample from Mexico (EF658643 - Puerto Morelos, Quintana Roo) being the most divergent. The two new species of Laurenciella from Florida, La. mayaimii and La. sp., formed an assemblage with La. marilzae with full support, and the interspecific divergence was high for both molecular markers. Laurenciella mayaimii is characterized mainly by its brownish-yellow main axis and cylindrical, alternate to subopposite branchlets, anastomoses between branches in the basal portions, and a single 'corps en cerise' present in each cortical cell and in trichoblasts. In addition, the walls of the cortical cells near the apices project, and lenticular thickenings are absent. The finding of Laurenciella in Biscayne Bay and Key Largo, South Florida expands its geographic distribution to western Atlantic lower subtropical waters.