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Cryptomycota ('hidden fungi'), Rozellida, or Rozellomycota are a clade of micro-organisms that are either fungi or a sister group to fungi. They differ from classical fungi in that they lack cell walls at any Food web stage in their lifecycle, as reported by Jones and colleagues in 2011. Despite their unconventional phagocytic feeding habits (typical fungi are osmotrophic), chitin has been observed in the inner layer of , and in immature resting spores for some species of Rozella, as indicated with Calcofluor-white as well as the presence of a fungal-specific chitin synthase gene.
The term "Rozellida" was coined in 2010, as it was found that the formally described genus Rozella, previously considered a chytrid, is rather close to LKM11 and other newly-discovered environmental DNA sequences.
Additional members of the group were isolated in 2011 by a team led by Thomas Richards, from the Natural History Museum in London, and also an evolutionary geneticist at the University of Exeter, UK. The team used DNA techniques to disclose the existence of unknown genetic material dredged from the university pond. Once they had a few unknown sequences they fluorescence labeled small DNA sequences and let them bind to the matching DNA in the whole sample (fluorescence in situ hybridization). Under fluorescence microscopy, they could see that the possessor cells were ovoid in shape and 3–5 across. They then established that the Cryptomycota were present in other samples taken from further freshwater environments, soils and marine sediments.
The common characteristic of the clade members known as of 2011 is that they lack the chitinous present in almost all previously discovered fungi (including microsporidia) and which are a major feature of the kingdom. Without the chitin the Cryptomycota can be phagotrophic parasites that feed by attaching to, engulfing, or living inside other cells. Most known fungi feed by osmotrophy—taking in nutrients from outside the cell.
Despite their unconventional phagocytic feeding habits (typical fungi are osmotrophic), chitin has been observed in the inner layer of , and in immature resting spores for some species of Rozella, as indicated with Calcofluor-white as well as the presence of a fungal-specific chitin synthase gene.
An 2014 rDNA analysis by Karpov et al. considers the group, which they now call "Cryptomycota", sister to Microsporidia. The same article lead to the concept of Opisthosporidia (Aphelid + Cryptomycota + Microsporidia), which as a whole was found in the analysis to be sister to fungi.
Also in 2014, Corsaro et al. discovered two new endonucleoparasites they termed Paramicrosporidium. Their SSU rDNA sequences allowed the authors to find that Microsporidia is nested in the Rozellids (which they call "Rozellomycota"). In the same year, they discovered a living Nucleophaga amoebae (described in 1895 and previously also considered a chytrid) and sequenced its SSU rDNA, placing it in Rozellomycota. Both of these genera are shown to branch out in the path connecting Rozella and Microsporidia. These two genera show morphological features similar to both Rozella and Microsporidia, and as a result provide some explanation for the large difference between the two.
In 2018, Tedersoo et al. performed a large phylogenetic study on fungi and related taxa to establish a new set of high-ranking taxa. Trees were built using SSU rDNA, RPB1 protein, and RPB2 protein. The study once again confirmed that Microsporidia belongs in Rozellomycota. After the 2020 Outline of Fungi and fungus-like taxa has accepted the conclusion (and provided an even bigger SSU rDNA tree), it is generally accepted that Microsporidia does, in fact, belong in the Rozellomycota.
The 2020 Outline discusses the related issue of expanding Microsporidia to include Nucleophaga, Paramicrosporidium, Morellospora and Mitosporidium (equivalent to "node 1" above) by Bass et al. (2018), though at that time Opisthosporidia was still thought to be a clade.
There is also the less radical idea of expanding Microsporidia to include the entire clade sister to Nucleophaga. The Outline currently chooses not to, while Corsaro et al. 2020 does and labels the old clade as "classical Microsporidia". The Corsaro idea is labeled as "Microsporidia s.l." in the above.
The branch leading to Rozella ("node 2") is also known as:
The following has unsure placement in the tree:
Phylogeny
Phylogeny of Rozellomycota. Backbone from Wijayawardene et al. (2020), later insertions to the tree referenced by footnotes.
Approaches to circumscription
There are some unresolved issues in cutting up the phylogeny. The main question is that since Rozella branches off early in the phylogeny, some authors elect to give the genus a phylum of its own, giving the rest of the tree ("node 1") a separate "Microsporidiomycota" which would also include LKM11. The relatively authoritative Outline does not divide in such a way, electing to use one phylum ("node 0") like Tedersoo et al. (2018) and Wijayawardene et al. (2018) have done.
Synonymy
The broadest node (node 0; Rozellomycota as interpreted by Outline) has also been known as:
Additional names not recognized by the Outline
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