Rozella is a fungal genus of obligate endoparasites of a variety of hosts, including Oomycota, Chytridiomycota, and Blastocladiomycota.[2][3][4] Rozella was circumscribed by French mycologist Marie Maxime Cornu in 1872.[5] Considered one of the earliest diverging lineages of fungi, the widespread genus contains 27 species, with the most well studied being Rozella allomycis.[6][7] Rozella is a member of a large clade of fungi referred to as the Cryptomycota/Rozellomycota. While some can be maintained in dual culture with the host, most have not been cultured, but they have been detected, using molecular techniques, in soil samples, and in freshwater and marine ecosystems. Zoospores have been observed, along with cysts, and the cells of some species are attached to diatoms.[8]
Rozella species grow inside their hosts. At first, the thallus is unwalled and indistinguishable from the host. As growth continues, the thallus will either form a zoosporangium using the wall of the host or a thick-walled resting spore that can be smooth or spiny.[9] From its conception, there have been two divergent morphologies within the genus. Monosporangiate species form a single zoosporangium within the host. Polysporangiate species form multiple zoosporangia that are separated with septa.[7]
Most described species are parasites of Oomycota, Chytridiomycota, and Blastocladiomycota. Rozella itersoniliae is a parasite of the basidiomycete Itersonilia perplexans,[7] though some authors doubt its placement in the genus.[4] Rozella coleochatis parasitizes a species of the green alga Coleochaete.[7]
The genus name of Rozella is in honour of Ernest Roze (1833–1900), who was a French Administrator and high official in the Ministry of Finance of France, botanist (Bryology, Mycology and Algology).[10]
French mycologist Marie Maxime Cornu in 1872 circumscribed the genus to accommodate four species: R. septigena, R. monoblepharidis-polymorphae, R. rhipidii-spinosi, and R. apodyae-brachynematis. Later authors shortened these to R. septigena, R. monoblepharidis, R. rhipidii, and R. apodyae. Based on the monosporangiate/polysporangiate differences in development and morphology, Fischer circumscribed Pleolpidium using R. monoblepharidis as the type and leaving R. septigena as the type species in Rozella. Clemonts and Shear also designated R. setigena as the type of Rozella in 1931. Later, R. allomycis and R. achlyae were described, and later authors treated Pleolpidium as a synonym of Rozella. Batko later circumscribed Skirgiella to accommodate the polysporangiate species and retained the monosporangiate species in Rozella. However, because this removed the type from the genus, it was nomenclaturally invalid. Additionally, molecular phylogenies consistently group monosporangiate and polysporangiate species together, thus validating the monophyly of the genus.[7]
Traditionally, Rozella has been classified as a member of Chytridiomycota, either as a member of Chytridiales[9] or Spizellomycetales.[4] However, molecular phylogenies place it well outside of Chytridiomycota with a plethora of environmental sequences.[11][2][12][13] There is considerable debate over the name of this larger clade: Cryptomycota, Rozellida, Rozellamycota.[7][14]