Holomycota or Nucletmycea are a basal Opisthokont clade as sister of the Holozoa. It consists of the Cristidiscoidea and the kingdom Fungi. The position of nucleariids, unicellular free-living phagotrophic amoebae, as the earliest lineage of Holomycota suggests that animals and fungi independently acquired complex multicellularity from a common unicellular ancestor and that the osmotrophic lifestyle (one of the fungal hallmarks) was originated later in the divergence of this eukaryotic lineage. Opisthosporidians is a recently proposed taxonomic group that includes aphelids, Microsporidia and Cryptomycota, three groups of endoparasites.
Rozella (Cryptomycota) is the earliest diverging fungal genus in which chitin has been observed at least in some stages of their life cycle, although the chitinous cell wall (another fungal hallmark) and osmotrophy originated in a common ancestor of Blastocladiomycota and Chytridiomycota, which still contain some ancestral characteristics such as the flagellum in zoosporic stage. The groups of fungi with the characteristic hyphal growth, Zoopagomycota, Mucoromycotina and Dikarya, originated from a common ancestor ~700 Mya. Zoopagomycota are mostly pathogens of animals or other fungi, Mucoromycotina is a more diverse group including parasites, saprotrophs or ectomycorrhizal. Dikarya is the group embracing Ascomycota and Basidiomycota, which comprise ~98% of the described fungal species. Because of this rich diversity, Dikarya includes highly morphologically distinct groups, from hyphae or unicellular yeasts (such as the model organism Saccharomyces cerevisiae) to the complex multicellular fungi popularly known as mushrooms. Contrary to animals and land plants with complex multicellularity, the inferred phylogenetic relationships indicate that fungi acquired and lost multicellularity multiple times along Ascomycota and Basidiomycota evolution.
