New species of freshwaterUlva,Ulva limnetica(Ulvales, Ulvophyceae) from the Ryukyu Islands, Japan

SUMMARY Ulva limneticaIchihara et Shimada, sp. nov. (Ulvales, Ulvophyceae) is described from the Ryukyu Islands, Japan, and is characterized by thalli that are: (i) branched, tubular, fragile and wrinkled; (ii) up to 80 cm in height and up to 2 cm in diameter; (iii) light to yellowish green in color; and (iv) having an asexual reproduction by means of quadriflagellate swarmers. Rhizoidal cells bear tubular extensions on the outside of the cell layer in the stipe.Ulva limneticais distinguished from species with similar thalli by chloroplast disposition, branching pattern, number of pyrenoids per cell and gross morphology. It is also distinguished by sequences of the nuclear‐encoded 18S ribosomal RNA gene, internal transcribed spacer 2 region and the plastid‐encoded large subunit of ribulose‐1,5‐bisphosphate carboxylase/oxgenase gene (rbcL).Ulva limneticawas clustered with otherUlvaspecies in an early diverging lineage within the genus.