, a parasite of green algae, is probably conspecific with , a parasite of red algae.

The genus () of the includes several species of holocarpic obligate aquatic parasites. These organisms are widely occurring in marine and freshwater habitats, mostly infecting filamentous green algae. Presently, all species are only known from their morphology and descriptive life cycle traits. None of the seven species classified in including the type species, has been rediscovered and studied for their molecular phylogeny, so far. Originally, the genus was established to accommodate all parasites of filamentous marine green algae. In the past few decades, however, has undergone multiple taxonomic revisions and several species parasitic in other host groups were added to the genus. While the phylogeny of the marine rhodophyte- and phaeophyte-infecting genera and , respectively, has only been resolved recently, the taxonomic placement of the chlorophyte-infecting genus remained unresolved. In the present study, we report the phylogenetic placement of infecting the filamentous marine green algae sampled from Skagaströnd in Northwest Iceland. Phylogenetic reconstructions revealed that is either conspecific or at least very closely related to the type species of , . Consequently, the type species of genus , , is reclassified to . Further infection trials are needed to determine if and are conspecific or closely related. In either case, the apparently recent host jump from red to green algae is remarkable, as it opens the possibility for radiation in a largely divergent eukaryotic lineage. Buaya AT, Scholz B, Thines M (2021). , a parasite of green algae, is probably conspecific with , a parasite of red algae. 223-231. doi: 10.3114/fuse.2021.07.11.