Holocarpic oomycete parasitoids of red algae are not .

is a genus of obligate holocarpic endobiotic oomycetes. Most of the species classified in the genus are known only from their morphology and life cycle, and a few have been examined for their ultrastructure or molecular phylogeny. However, the taxonomic placement of all sequenced species is provisional, as no sequence data are available for the type species, , to consolidate the taxonomy of species currently placed in the genus. Thus, efforts were undertaken to isolate from its type host, and to infer its phylogenetic placement based on 18S rDNA sequences. As most species of for which sequence data are available are from rhodophyte hosts, we have also isolated the type species of the rhodophyte-parasitic genus , and obtained partial 18S rDNA sequences. Phylogenetic reconstructions in the current study revealed that from forms a monophyletic group with a morphologically similar isolate from , and a morphologically and phylogenetically more divergent species from . However, they were widely separated from a monophyletic, yet unsupported clade containing and red algal parasites previously classified in . Consequently, all holocarpic parasites in red algae should be considered to be members of the genus as previously suggested by some researchers. In addition, a new species of , is introduced to accommodate the pathogen of .