Barcoding the green macroalgae (Ulvophyceae) from the Alagoas coast: new records and an updated checklist

Abstract Marine green macroalgae remain poorly characterized along much of the Brazilian coast, particularly in Alagoas, where most records rely exclusively on morphology. This study aimed to assess the diversity of Ulvophyceae along the Alagoas coast using DNA barcoding and to provide a revised state checklist, including new geographic records. Samples collected from eight reef and estuarine sites were examined morphologically and analyzed using tuf A, rbc L, and LSU rDNA sequences and phylogenetic analysis. We generated 38 new sequences, and our phylogenetic analysis confirmed 20 species, comprising six Ulvales, five Bryopsidales, and nine Cladophorales. Molecular data revealed several discrepancies with morphology, especially in Ulva and Cladophorales, and exposed cryptic diversity within the Cladophora vagabunda and Boodlea composita–Phyllodictyon anastomosans complexes. Ulva tentaculosa is recorded for the first time in the Atlantic Ocean, U. meridionalis in the South Atlantic, U. chaugulei and U. tepida in northeastern Brazil, and U. ohnoi in Alagoas. The study adds five species to the known Ulvophyceae flora of Alagoas and revises the state total to 79 reported species, nearly twice the number listed in the national database. These findings demonstrate that morphology alone underestimates regional diversity and emphasize DNA barcoding as an essential tool for accurate identification, biodiversity monitoring, conservation, and improvement of public reference databases.