AppearanceThe fruit body has an irregular shape, and usually breaks through the bark of dead branches. It is up to 7.5 cm broad and 2.5 to 5.0 cm high, rounded to variously lobed or brain-like in appearance. The fruit body is gelatin-like but tough when wet, and hard when dry. The surface is usually smooth, the lobes translucent, deep yellow or bright yellow-orange, fading to pale yellow, rarely unpigmented and white or colorless. The fruit bodies dry to a dark reddish or orange. The spores, viewed in mass, are whitish or pale yellow.The basidia are ellipsoid to roughly spherical in shape, not or rarely stalked, and typically 15–21 µm wide. They contain two to four septa that divide it into compartments; the septa are most frequently diagonal or vertical. Asexual reproduction in ''T. mesenterica'' is carried out through the formation of spores called conidia, which arise from conidiophores—specialized hyphal cells that are morphologically distinct from the somatic hyphae. The conidiophores are densely branched and normally abundant in the hymenium; young specimens may be entirely conidial. The conidia are roughly spherical, ovoid, or ellipsoid, and about 2.0–3.0 by 2.0–2.5 µm. They may be so numerous that young fruit bodies may be covered in a bright yellow, conidial slime. The spores are broadly ellipsoid to oblong, on average 10.0–16.0 by 6.0–9.5 µm; they germinate by germ tube or by yeast-like conidia of identical form to the conidia produced on the conidiophores.
Naming''Tremella mesenterica'' is frequently confused with ''Tremella aurantia'', a widespread species parasitic on the plant pathogenic fungus ''Stereum hirsutum''. ''Tremella aurantia'' can often be recognized by the presence of its host, which typically grows on logs, stumps, and trunks. Though the two species are similarly colored, the surface of ''T. aurantia'' is usually matte, not greasy or shiny, and its lobes or folds are thicker than those of ''T. mesenterica''. Fruit bodies of ''T. aurantia'' contain unclamped, thick-walled host hyphae and consequently retain their shape when dried, rather than shriveling or collapsing to a film . Microscopically, ''T. aurantia'' has smaller basidia and smaller, differently shaped spores measuring 8.5–10 by 7–8.5 µm. ''T. brasiliensis'', known from neotropical areas and Japan, and the North American species ''T. mesenterella'' are also similar.
''Tremella mesenterica'' may also be confused with members of the Dacrymycetaceae family, like ''Dacrymyces chrysospermus'' , due to their superficial resemblance. Microscopic examination shows that the Dacrymycetaceae have Y-shaped basidia with two spores, unlike the longitudinally split basidia characteristic of ''Tremella''; additionally, ''D. chrysospermus'' is smaller, has a whitish attachment point to its substrate, and grows on conifer wood.
Distribution''Tremella mesenterica'' has a cosmopolitan distribution, having been recorded from Europe, North, Central, and South America, Africa, Asia, and Australia. Fruit bodies are formed during wet periods throughout the year. In British Columbia, Canada, it is sometimes found on maple, poplar, or pine, but is most abundant on red alder. It prefers to grow in habitats ranging from mesic to wet. The fungus grows parasitically on the mycelium of wood-rotting corticioid fungi in the genus ''Peniophora''. Occasionally, ''T. mesenterica'' and its host fungus can be found fruiting together.
Behavior''Tremella mesenterica'' has a yeastlike phase in its life cycle that arises as a result of budding of basidiospores. The alternation between asexual and sexual propagation is achieved by mating of yeast-form haploid cells of two compatible mating types. Each mating type secretes a mating pheromone that elicits sexual differentiation of the target cell having the opposite mating type to the pheromone-producing cell. The sexual differentiation is characterized by the arrest of the growth in the G1 phase of the cell division cycle and subsequent formation of an elongated mating tube. Formation of the mating tube, initiated by the pheromones A-10 and a-13, is similar to the process of bud emergence during bipolar budding in yeasts. Tremerogen A-10 has been purified and its chemical structure found to be ''S''-polyisoprenyl peptide. Fruit bodies arise from a primordium located beneath the wood bark, and sometimes more than one fruit body can originate separately from the same primordia.
Habitat''Tremella mesenterica'' has a cosmopolitan distribution, having been recorded from Europe, North, Central, and South America, Africa, Asia, and Australia. Fruit bodies are formed during wet periods throughout the year. In British Columbia, Canada, it is sometimes found on maple, poplar, or pine, but is most abundant on red alder. It prefers to grow in habitats ranging from mesic to wet. The fungus grows parasitically on the mycelium of wood-rotting corticioid fungi in the genus ''Peniophora''. Occasionally, ''T. mesenterica'' and its host fungus can be found fruiting together.
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