Updating the Ulvaceae in the green seaweeds of Britain and Ireland

The 2007 flora “Green Seaweeds of Britain and Ireland” did not present the molecular data underpinning the Ulvaceae treatment, mostly ITS sequences. Subsequently, names have changed as type material of Ulva species is sequenced and intensive sampling with DNA barcoding adds new European species. To update the Ulvaceae, we systematically sampled from 2007 to 2021, identifying specimens using various molecular markers alongside DNA from type material of four species. We show here that Ulva gigantea, based on rbcL, tufA and ITS sequences of its holotype, is assigned to Ulva compressa, as is the lectotype of Ulva curvata. Ulva gigantea sensu GenBank and Ulva pseudocurvata are conspecific. The correct name is U. pseudocurvata based on rbcL sequences of the lectotype. Two species of monostromatic Ulvaceae were included in the 2007 flora, but we show that both of them and all earlier British monostromatic collections represent Ulvaria splendens, a species originally described from Alaska. Analysis of two rbcL amplicons of the Ulva sordida lectotype shows that it is conspecific with Ulvaria splendens. Our first genuine collections of Ulvaria obscura from SW England and SW Wales correspond to topotype material from the Bay of Biscay, recent samples from Galicia and unpublished tufA sequences from Britanny.