Tremella
Tremella is a genus of fungi in the family Tremellaceae. All "Tremella" species are parasites of other fungi and most produce anamorphic yeast states. Basidiocarps (fruit bodies), when produced, are gelatinous and are colloquially classed among the "jelly fungi". Over 100 species of "Tremella" (in its wide sense) are currently recognized worldwide. One species, "Tremella fuciformis", is commercially cultivated for food. Taxonomy. History. "Tremella" was one of the original genera created by Linnaeus in his "Species Plantarum" of 1753. The name comes from the Latin "tremere" meaning "to tremble". Linnaeus placed "Tremella" in the algae, including within it a  variety of gelatinous growths, including seaweeds, cyanobacteria, and myxomycetes, as well as fungi. Subsequent authors added additional species to this mix, until Persoon revised "Tremella" in 1794 and 1801, repositioning the genus within the fungi. Persoon's reinterpretation of "Tremella" was sufficiently radical to be considered a separate genus ("Tremella" Pers.) from that originally created by Linnaeus ("Tremella" L.). Tremella Pers. has now been conserved under the International Code of Nomenclature for algae, fungi, and plants, with "Tremella mesenterica" as the type species. Current status. Molecular research, based on cladistic analysis of DNA sequences, has shown that "Tremella" (as previously  understood) is polyphyletic (and hence artificial), with most species not closely related to the type. Accordingly, some species have been transferred to new genera and new families: "Tremella foliacea" and related species are now placed in the genus "Phaeotremella" within the family Phaeotremellaceae; "Tremella encephala" and related species are now placed in the genus "Naematelia" within the Naemateliaceae; "Tremella moriformis" and related species are now placed in the genus "Pseudotremella" within the Bulleraceae; and "Tremella polyporina" is now placed in the genus "Carcinomyces" within the Carcinomycetaceae. Several other species groups have not yet been renamed, pending further research. More than  500 species have been described in "Tremella", but most of these are old names of doubtful application or old names for species later transferred to other genera. In its strict sense, the genus "Tremella" now contains some 30-40 species, including the type "Tremella mesenterica" and the cultivated species "T. fuciformis". Description. Fruit bodies (when present) are gelatinous. In some species they are small (under 5 mm across) and pustular to pulvinate (cushion-shaped). In others they are much larger (up to 150 mm across) and may be variously lobed, cephaliform (like a brain, with folds and ridges), or foliose  (with leaf-like or seaweed-like fronds). Many "Tremella" species, however, are hymenial parasites, producing spores within the fruit bodies of their hosts, and are only visible microscopically. Microscopic characters. "Tremella" species produce hyphae that are typically (but not always) clamped and have haustorial cells from which hyphal filaments seek out and penetrate the hyphae of the host. The basidia are "tremelloid" (globose to ellipsoid, sometimes stalked, and vertically or diagonally septate), giving rise to long, sinuous sterigmata or epibasidia on which the basidiospores are produced. These spores are smooth, globose to ellipsoid, and germinate by hyphal tube or by  yeast cells. Conidiophores are often present, producing conidiospores that are similar to yeast cells. Habitat and distribution. Species are mainly parasitic on wood-rotting fungi in the phyla Ascomycota and Basidiomycota, particularly on species that occur on dead attached branches. Hosts include members of the corticioid fungi and Dacrymycetales in the Basidiomycota and species of "Diaporthe", other Sordariomycetes, and lichens in the Ascomycota. Some "Tremella" species parasitize the fruit bodies of their hosts, others parasitize the mycelium within the wood. As a group, "Tremella" species occur worldwide, though individual species may have a more restricted distribution. Species and hosts. The  list below includes species of "Tremella" (in the wide sense) that have recently been described or redescribed based on fruit bodies. Species based on yeasts are not included. Some additional older species may also be valid, but lack a modern description. The type locality (but not the wider distribution) is given for each species together with the host fungus, where known. Species belonging to "Tremella" in the strict sense are marked as such, as are those that have been transferred to new genera.