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Species Information
Summary: Polyporus tuberaster has a yellowish brown cap with darker scales, white to pale tan decurrent pores, and a central to lateral stem with a black base. It arises from a large, rubbery to rock hard, blackish sclerotium that incorporates debris and dirt. The sclerotium is sold in European markets, and if well watered will produce fruiting bodies for eating (Lincoff). According to Paul Kroeger (pers. comm.) the sclerotium has been mistaken for old pemmican.
Gilbertson(1) show records on a map from CA and AZ, but give distribution as "Western United States south to Arizona in the aspen zone and Southern Canada, widespread in the northern boreal zone", in Canada this fungus occurs in the aspen parkland belt of the prairies, (Schalkwijk-Barendsen who illustrates it from AB, and mentions its occurrence in Netherlands, Italy, and Switzerland), known from BC, AB, SK, WA, OR, CA, and AZ, in western North America, (Ginns). It also occurs in Eurasia (Breitenbach).
Cap: up to 15cm across, 0.5-1.5cm thick, simple when on wood, often more compound when on the ground, circular to semicircular or even fan-shaped in compound fruitbodies, depressed in center, fleshy when fresh; whitish, ochraceous to pale yellowish brown; "covered with small tan to dark brown scales with a broad base and especially towards margin, split and fibrillose, in pale specimens the scales are pale and thus not especially distinct", when old becoming more bald from center as scales partly wear away, partly are glued to surface; margin thin and mostly finely ciliate [fringed with fine hairs] or torn, (Gilbertson), 4-15cm, convex to flat with depressed or umbilicate center, "margin often indented or lobed"; tan to brown or ocher, darker when old; dry, developing darker brown fibrils or fibrillose scales often radially arranged, (Arora)
Flesh: up to 1cm thick, "fleshy-tough when fresh, drying rigid and brittle"; white, (Gilbertson), thin, rigid when dry; pallid, (Arora)
Pores: 1-2mm long and 0.5-1mm wide, decurrent, "often lacerate to dentate, angular, often somewhat radially elongated"; white to pale tan; tube layer up to 0.5cm thick, colored as pores, (Gilbertson), 1-3 per mm, usually decurrent; white to pale tan; tube layer 0.1-0.3cm thick, (Arora)
Stem: 0.5-6cm x 0.5-1.5cm, central to lateral, straight or curved at base; white to ochraceous except "at base with white hairs under which there is a thin black cuticle which may extend a short distance above the tomentum"; sclerotium "normally present in the ground, round to oval or irregular, heavy, up to 30 lbs, but normally far less than that, fleshy and tough when fresh, shrinking considerably on drying and becoming hard and brittle, surface ochraceous to dark dirty brown, densely mixed with sand, stones and roots, often in considerable quantities so it looks like ground material has been penetrated by mycelial strands and white spots of hyphae", (Gilbertson), 2.5-10(20)cm x 1-2.5(4)cm, "more or less equal, central or off-center", solid, tough; brown or cap-colored; arising from a large brown to black underground sclerotium that is rubbery when fresh but rock hard when dry, exterior of sclerotium "rough and irregular", "interior often marbled with blackish-brown and paler areas and usually full of dirt and debris", (Arora), underground sclerotium round to irregular, black, fleshy, tough, heavy (up to 13 kg), and large (about 15cm in diameter), (Ginns), sclerotium gristly and rubbery, with a black and gray pattern, (Schalkwijk-Barendsen)
Microscopic: spores 10-16 x 4-7 microns, cylindric to oblong elliptic, inamyloid, colorless; basidia 4-spored, 25-40 x 6-10 microns, clavate, with basal clamp; cystidia absent; hyphae dimitic, generative hyphae 3-9 microns wide, with clamp connections; hairs at base of stem and the scales mostly of wide generative hyphae; "binding hyphae of the Bovista type with tapering sidebranches, thick-walled to solid, sparingly branched, up to 12 microns in the main stem"; "sclerotium mainly with binding hyphae, in parts very finely branched and very thin, in most parts sparingly branched, thick-walled and variable in diameter, 3-10 microns wide, in some cases with apical swellings", (Gilbertson), spores 10-16 x 3.5-6 microns, cylindric, smooth, (Arora)
Spore Deposit: white (Arora)
Habitat / Range
annual, on hardwoods or on the ground from a large blackish sclerotium (even on wood, there is often a connection through wood to underground sclerotium), causing a white rot of hardwoods, (Gilbertson), spring, late summer, fall, (Bacon)
Similar Species
Polyporus squamosus has similar cap scales but 1) it has no sclerotium, 2) it normally has thicker more robust fruitbody, and 3) scales "are normally rounded and more agglutinated and not raised and tufted as in P. tuberaster", (Gilbertson). Polyporus umbellatus fruitbodies sometimes develop from a "branched, elongated, finger-shaped, black" sclerotium 1-2cm in diameter, (Ginns(28)). Polyporus radicatus and Polyporus melanopus develop root-like underground structure.
