Morphological and molecular studies on the genus Gayralia (Ulotrichales, Chlorophyta) in northeastern Brazil with expansion of its species distribution

The genus Gayralia has a complex taxonomy, often with morphological and ontogenetic characteristics that overlap with those of other monostromatic green algae, mainly Monostroma. Molecular studies of monostromatic green algae are still rare, especially in Brazil, where G. brasiliensis was described originally. Considering the difficulties in delimiting genera and species based on morphological criteria, we investigated the genus Gayralia through ITS sequencing of field collections in the tropical northeastern region of Brazil. Our 14 newly generated sequences formed a fully supported clade with G. brasiliensis showing low intraspecific divergence (0–0.6%). The distribution of G. brasiliensis in Brazil was expanded to the northeastern Brazilian coast, with the first record for the states of Rio Grande do Norte, Paraíba, Alagoas, and Sergipe. In addition, two sequences from India identified as G. “oxysperma” were grouped in the G. brasiliensis clade, indicating that they correspond to the same genetic species. This finding extends the geographical distribution of G. brasiliensis to India. Our results place Monostroma kuroshiense within the Gayralia clade, which warrants a new combination – Gayralia kuroshiensis (F.Bast) comb. nov.