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 are currently recognized worldwide. Two species, Tremella fuciformis and Tremella aurantialba, are commercially cultivated for food. 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 Botanical Nomenclature, with Tremella mesenterica as the type species. Molecular research, based on cladistic analysis of DNA sequences, suggests that Tremella is polyphyletic (and hence artificial), the genus not being clearly separated from other genera within the Tremellaceae. Comparatively few species, however, have yet been sequenced. 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. Over 100 species are currently accepted within the genus. 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. 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. 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, polypores, 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 (sometimes incorporating host hyphae), others parasitize the mycelium within the wood.