Species diversity and molecular phylogeny of tubular Ulva (Ulvaceae, Ulvophyceae) in Taiwan, including U. taiwanifretensis sp. nov

Tubular Ulva species are a prominent component of marine macroalgal communities along the coasts of Taiwan. However, their species diversity remains poorly known. Here, we sequenced and examined collections made over the past 15 years from various habitats in Taiwan. RbcL phylogenetic analyses identified 12 species, and these were largely confirmed by tufA analyses. These included a new species (U. taiwanifretensis sp. nov.), four species recorded for the first time from Taiwan (U. flexuosa subsp. linziformis, U. tepida, U. torta and U. tentaculosa), four undescribed taxa, and three previously reported species [U. aragoënsis (previously recorded as U. linza), U. prolifera, U. meridionalis]. In contrast, three tubular species previously recorded in Taiwan (U. clathrata, U. compressa and U. intestinalis) were not detected in this study. These species may have been misidentified as their tubular morphology superficially resembles that of U. aragoënsis or U. prolifera. Notably, U. taiwanifretensis sp. nov. from the Taiwan Strait is morphologically similar to U. intestinalis.