Diversity of the green macroalgal genus Ulva (Ulvophyceae, Chlorophyta) from the east and gulf coast of the United States based on molecular data

Ulva (Ulvophyceae, Chlorophyta) is common in intertidal environments and can also be found in freshwater ecosystems. The difficulty to morphologically identify Ulva species due to cryptic diversity and morphological plasticity has caused a taxonomic conundrum. Fortunately, molecular data have begun to unravel a better understanding of its diversity. Here, we present a molecular analysis with 247 samples of Ulva from the Gulf of Mexico and Atlantic USA based on chloroplast (rbcL and tufA) and nuclear (ITS1-5.8S-ITS2) molecular markers. Twenty-four Ulva taxa had previously been reported for this area based on morphology and earlier molecular studies mostly from Northeastern USA and Canada. In this study, sixteen Ulva clades were identified representing 13 named clades and putatively three undescribed species. Only nine of the 24 taxa previously reported for the Western Atlantic were confirmed. Four species were identified for the first time in the U.S. East and Gulf Coast (U. aragoensis, U. californica, U. meridionalis, and U. tepida). This study provides a foundation for future research on Ulva in this area and reiterates the necessity of using molecular-assisted identifications for this group.

Automated summary

Ulva is a common algae in intertidal and freshwater ecosystems, with difficulties in morphological identification due to cryptic diversity and morphological plasticity. Molecular data has helped to better understand its diversity. A study in the Gulf of Mexico and Atlantic USA identified 16 Ulva clades, including 13 named clades and potentially three undescribed species. Only nine of the previously reported 24 Ulva taxa in the Western Atlantic were confirmed, with four species identified for the first time in the U.S. East and Gulf Coast.