A mycoparasite most often seen on old, rotting bracket fungi, where it forms a loose, cobwebby white to yellowish subiculum dotted with a dense, pimply crust of tiny orange perithecia. Its asexual stage, Cladobotryum varium, is one of the agents of cobweb disease on cultivated mushrooms, reported on Agaricus bisporus and enoki (Flammulina velutipes).
Not edible. Discard mushrooms showing cobweb-like mould.
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Habitat
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Parasitic on the fruit bodies of rotting polypores (e.g. Polyporus durus, Trametes versicolor, Fomitopsis), also recorded on Armillaria. On farms, the asexual stage causes cobweb on mushroom crops.
Distribution
Widespread; recorded across the UK and Europe and in New Zealand. Cobweb caused by C. varium is reported from Korea.
Characteristics
Sexual stage: densely clustered, orange, pear-shaped perithecia up to about 0.3 mm across, on a loose white to yellowish cobwebby subiculum over the host's surface. KOH: perithecia and subiculum stain purple. Ascospores: two-celled, long, with sharp-pointed ends. Asexual stage (Cladobotryum varium): hyaline conidia; this cobweb-type mould is known on mushroom crops and occasionally on wild hosts such as honey fungus. Identification: microscopy and a KOH test are needed; sequence data for farm isolates.
