A new family, genus, and species record, Gayralia brasiliensis (Gayraliaceae, Ulotrichales, Chlorophyta) is reported in Singapore using chloroplast elongation factor Tu (tufA) and nuclear internal transcribed spacer (ITS) markers alongside gross and microscopic examination. This species was likely missed by previous surveys due to its limited local distribution, superficial similarity to the much more common Ulva, and its small size. Morphologically, G. brasiliensis in Singapore is more similar to G. oxysperma than to G. brasiliensis in Brazil. This study demonstrates the importance of integrative molecular and morphological analysis for characterising macroalgal diversity.