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The green seaweed Ulva is important from ecological and economic perspectives, but the identification of species is often problematic. Here we assessed and discussed different perspectives to establish a stable taxonomic framework for Ulva, which will benefit both ecological and applied research. We evaluated (1) the performance of commonly used DNA-barcode markers (ITS rDNA, rbcL, and tufA) using species delimitation methods (PTP and GMYC), (2) the usage of species names in the literature, and (3) the geographic coverage of genetic data to identify poorly sampled regions. Species delimitation employing the tufA gene was the most consistent across methods. Not surprisingly, DNA-based species delimitation was often in disagreement with traditional morphology-based species definitions. Biological species concepts, where tested, proved to be generally narrower than DNA-based species delimitation. Although the use of molecular markers has greatly improved our view of Ulva diversity, the names associated with DNA sequences in public databases are often unreliable, complicating species identification. Recently, sequencing type materials has considerably reduced the gap between DNA sequence data and Linnaean names, but our knowledge on Ulva diversity remains inadequate, especially in tropical regions. Perspectives for Ulva taxonomy include the consistent use of multiple DNA-barcode markers assisted by species delimitation methods, applications of genomic data, and crossing experiments. To arrive at a stable nomenclature, we outline the benefits and shortcomings of adhering to the rules and practices of the International Code of Nomenclature for algae, fungi, and plants, for example, by sequencing name-bearing types and discuss alternative approaches. [ABSTRACT FROM AUTHOR]

The green algal genus Ulva is widely distributed around all continents. Plants with both distromatic or monostromatic thalli now form a single taxon based on ITS rDNA and rbcL gene sequencing. Ulva is known to occupy several ecological niches including freshwater and marine (intertidal and subtidal) habitats, attributed to its tolerance to key determinants such as light, temperature, and salinity. The genus is perceived as model system to study life cycle, morphogenesis and development from simple to complex multicellularity. The life cycle is isomorphic and biphasic type, knowledge of which is important in developing viable cultivation techniques. The culture of Ulva is by photo-bioreactor, land-based, and open-sea farming producing about 1500 t dry annum−1 biomass. The understanding of scientific basis for eutrophication-driven green tide events is of paramount importance for coastal ecosystem management. Studies related to cross-kingdom cross-talk between Ulva and surrounding microbes have been recently undertaken through high-throughput techniques to understand their role in growth, development, and morphogenesis. Several regional species are rich in vital nutrients and thus qualify in the functional food sector, and recent research is poised to develop a bio-refinery model for complete utilization of feedstock. Ulva spp. are also used as a feed source in aquaculture and for environmental bioremediation. [ABSTRACT FROM AUTHOR]