Genetic analysis of Ulva (Ulvaceae, Chlorophyta) type specimens resolves northeast Pacific blade-forming species

Abstract

Misapplication of Ulva epithets in GenBank has led to confusion in the scientific literature and community. To solve some of the problems, targeted DNA sequencing of plastid encoded rbcL gene amplicons or high-throughput sequencing was performed on all blade-forming Ulva type specimens from the northeast Pacific. Recently collected specimens from at or near type localities were also analyzed for some taxa. Based on these genetic analyses, we confirmed currently recognized species: U. californica, with U. angusta and U. scagelii as heterotypic synonyms, U. stenophylla, U. taeniata, and U. tanneri. Ulva dactylifera, currently considered a synonym of U. taeniata based on morpho-anatomy, is recognized as a distinct species, as is U. expansa whose type specimen was sequenced in 2018. All but two of the ITS, rbcL and tufA sequences in GenBank that were labeled U. californica were correctly named, in contrast to U. taeniata, for which only one of 14 sequences was correctly labeled. These results show that DNA sequencing of Ulva type specimens is essential for the correct application of names.