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Grifola (order Polyporaceae) A genus of fungi in which the fruit body consists of a branched stem, each branch ending in a flattened, fan-like pileus. In G. frondosa the tuft of pilei may reach 40 cm across; each pileus measures 4–10 cm across, is leathery in texture, and typically has a greyish and wrinkled upper surface. The pores on the under-side are whitish and extend down the stem. This species has a distinctive odour of mice (acetamide). It is parasitic on trees, especially oak and beech, and grows at the base of the trunk.