Protohydnum is a genus of fungi in the order Auriculariales. Protohydnum cartilagineum, the type, occurs in Central and South America and produces effused, gelatinous basidiocarps (fruit bodies) on wood, wholly covered in small spines. Molecular research, based on cladistic analysis of DNA sequences, has shown that the genus is distinct, but that other similar-looking species previously referred to Protohydnum belong in the genera Hyalodon or Elmerina. More recent molecular research has shown that the genera Bourdotia and Ductifera, producing smooth, effused or lobed, gelatinous basidiocarps, are synonyms of Protohydnum.

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