Meripilus sumstinei is a large polypore that forms clustered rosettes of fan-shaped, whitish to brownish caps from a shared, branched base at the foot of hardwoods, especially oaks. Its pore surface and cap margins bruise dark brown to black when handled. It is the North American species that field guides long called Meripilus giganteus, a name now restricted to a European species.
Edible when young and fresh (Missouri Department of Conservation), with caution. Only young, soft caps or their soft outer edges are worth eating; older material turns leathery. Cook thoroughly and slowly; the flesh blackens and can stain other food. The closely related European M. giganteus is reported to upset some people's stomachs, so try a small portion first. Similar polypores (hen of the woods, Berkeley's polypore, cauliflower mushroom) do not bruise black.
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Habitat
Parasitic on the roots of living oaks and other hardwoods, and saprobic on dead stumps and deadwood; also reported on Douglas-fir. Grows in large clusters on the ground around the bases of trees and stumps, causing a white rot, and often returns to the same spot in later years. Summer and fall (July to September in Missouri).
Distribution
North America: widely distributed east of the Rocky Mountains, with occasional reports from the West (MushroomExpert); recorded statewide in Missouri. North American reports of Meripilus giganteus refer to this species; M. giganteus in the strict sense is European.
Characteristics
Fruiting body: a rosette of many overlapping caps on a branched, stemlike base, up to about 30 cm across (MushroomExpert); the Missouri Department of Conservation gives clusters up to about 80 cm (32 in). Caps: 5-20 cm across, fan-shaped, finely velvety or bald; whitish, becoming brownish with age, often radially streaked and concentrically zoned; the thin margin bruises and ages black. Pore surface: whitish, becoming dirty tan; bruising dark brown to black when fresh; 6-8 round to angular pores per mm; tubes up to 8 mm deep. Stem: short, tough, often off-center; whitish, becoming brown to blackish. Flesh: white, firm, somewhat stringy, blackening when cut. Odor and taste: mild. Spore print: white. Spores: 5-5.5 x 4.5-5 µm, inamyloid. Hyphal system monomitic; clamp connections absent (MushroomExpert).
