Tremella

Belongs within: Tremellales.

Tremella is a genus of fungi parasitic on other fungi. Fruiting bodies, when present, are gelatinous; many species also have an anamorphic yeast form.

Jelly and yeast

Browse the shelves of your local Asian grocer (or, if you happen to be in Asia, your grocer) and one product you are likely to find for sale is something that may be labelled as ‘white fungus’ or ‘snow fungus’. The frilled, sheet-like fruiting bodies of this fungus, Tremella fuciformis, are sold dried, and become jelly-like when soaked in water. White fungus does not have that much of a taste but is mostly used in Chinese and other eastern Asian cuisines to add texture to dishes (particularly desserts). As such, T. fuciformis is perhaps the most familiar representative of the jelly fungi of the genus Tremella.

A large number of species of Tremella have been described around the world, often found growing on wood or other fungi. Defining the genus has been a challenge owing to their multi-stage life cycle and wide divergence in fruiting morphology between species. Representatives are united by the morphology of septal pores within hyphae and structure of the meiotic spore-producing basidia (Zamora et al. 2016). Fruiting bodies (basidiocarps), if well developed, are typically frond-like and gelatinous. However, many species are microscopic and basidiocarps are inconspicuous. Many species also produce asexual conidia, often in association with the basidiocarp (Bandoni & Boekhout 2011). Molecular phylogenetic analyses have not supported Tremella in its current state as monophyletic but the issue remains unresolved.

After their release from the basidiocarp, Tremella basidiospores do not directly germinate into hyphae but instead bud into yeast cells. Tremella species may remain in the yeast phase indefinitely, continuing to divide and multiply, until two yeast cells of compatible reproductive strains come into contact. The two yeast cells will then fuse to produce a dikaryotic hypha.

Whereas Tremella in the yeast stage are presumably independent saprobes, in the hyphal stage they are all more or less associated with other fungi. Tremella hyphae latch onto host hyphae via specialised haustoria, through which they leach nutrients. The degree to which Tremella species are obligate parasites or capable of obtaining their own nutrients saprobically is not always clear and presumably varies between species. Tremella fuciformis, for instance, is cultured commercially on sawdust that has also been inoculated with its host, the ascomycete Annulohypoxylon archeri. Laboratory studies have indicated that T. fuciformis is capable of independent growth (Bandoni & Boekhout 2011) but the host is still necessary for economically viable production. Conversely, lichenicolous micro-Tremella may grow entirely embedded within their lichen host (Zamora et al. 2016), from which they presumably obtain all their nutrients. Parasitism, after all, is a matter of degrees.

Systematics of Tremella

Characters (from R. J. Bandoni): Sporocarps conidial or basidial; conidia not arising as conjugating pairs; basidia typically single, terminal, rarely catenate and virtually always producing epibasidia and ballistospores; basidiospores mostly abstricted forcibly.

Tremella Pers. 1794 (nom. cons.)KC01 (see below for synonymy)
    |--T. albidaKC01
    |--T. caloceraticolaKS01
    |--T. encephalaKS01
    |--T. exiguaKS01
    |--T. foliaceaKS01
    |--T. fuciformisKS01
    |--T. giraffaKS01
    |--T. globisporaKS01
    |--T. mesentericaKS01
    |--T. meteorica [=*Actinomyce meteorica]S92
    |--T. microsporaKS01
    |--T. moriformisKS01
    |--T. mycophagaKS01
    |    |--T. m. var. mycophagaKS01
    |    `--T. m. var. obscuraKS01
    |--T. neofoliaceaKS01
    |--T. nivalisKS01
    |--T. occultiferoideaKS01
    |--T. penetransKS01
    |--T. simplexKS01
    `--T. taiwanensisKS01

Tremella Pers. 1794 (nom. cons.)^KC01 [incl. Actinomyce Meyen 1827 (nom. rej.) non Actinomyces Harz 1877^S92, Corticioides Lloyd 1908^KC01, Dermatangium Velen. 1926^KC01, Encephalium Link 1816^KC01, Epidochium Fr. 1849^KC01, Gelatina Raf. 1806^KC01, Gyraria Nees 1816^KC01, Hepataria Raf. 1808^KC01, Nakaiomyces Kobayasi 1939 (n. d.)^KC01, Phaeotremella Rea 1912^KC01]

*Type species of generic name indicated

References

Bandoni, R. J., & T. Boekhout. 2011. Tremella Persoon (1794). In: C. P. Kurtzman, J. W. Fell & T. Boekhout (eds) The Yeasts: A taxonomic study 5^th ed. vol. 3 pp. 1567–1590. Elsevier.

[KC01] Kirk, P. M., P. F. Cannon, J. C. David & J. A. Stalpers. 2001. Ainsworth & Bisby’s Dictionary of the Fungi 9^th ed. CAB International: Wallingford (UK).

[KS01] Kirschner, R., J. P. Sampaio, M. Gadanho, M. Weiß & F. Oberwinkler. 2001. Cuniculitrema polymorpha (Tremellales, gen. nov. and sp. nov.), a heterobasidiomycete vectored by bark beetles, which is the teleomorph of Sterigmatosporidium polymorphum. Antonie van Leeuwenhoek 80: 149–161.

[S92] Schaal, K. P. 1992. The genera Actinomyces, Arcanobacterium, and Rothia. In: Balows, A., H. G. Trüper, M. Dworkin, W. Harder & K.-H. Schleifer (eds) The Prokaryotes: A handbook on the biology of bacteria: Ecophysiology, isolation, identification, applications 2^nd ed. vol. 1 pp. 850–905. Springer-Verlag: New York.

Zamora, J. C., A. M. Millanes, M. Wedin, V. J. Rico & S. Pérez-Ortega. 2016. Understanding lichenicolous heterobasidiomycetes: new taxa and reproductive innovations in Tremella s.l. Mycologia 108 (2): 381–396.