Summary:
{See also Stereum Table.} Care must be taken not to confuse this genus with Trametes (see Polypore category), whose underside will reveal pores when examined with a hand lens. |Features of Stereum hirsutum include 1) growth on hardwood, and occasionally conifer wood, 2) elastic, tough fruitbody that is semicircular to fan-shaped, usually shingled and forming rows, but may be resupinate, or bent outward from resupinate surface to form a shelf, 3) cap surface that is hairy-tomentose, zoned, yellow-orange to reddish brown with grayish white tomentum, with wavy surface and margin, the margin lobed and lighter in color, 4) spore-bearing surface that is grayish to yellowish, ochraceous, pale orange or orange-brown (with a whitish margin in actively growing specimens), not generally turning red when bruised, 5) spores that are narrowly elliptic to cylindric, smooth, weakly amyloid, and colorless, 6) conducting hyphae ending in pseudocystidia, and also sharp-tipped hyphidia present, 7) 2 types of hyphae, neither with clamp connections: thin-walled to thick-walled and branching, and thick-walled, branching less. |Stereum complicatum, Stereum gausapatum, Stereum hirsutum, and Stereum ochraceoflavum are members of the subgenus Stereum, having sharp tipped hyphidia but lacking the pseudoacanthohyphidia found in subgenus Aculeatostereum. The Stereum hirsutum complex according to Welden(4) in 1971, referred to in Chamuris(4) in 1985, includes 1) Stereum hirsutum, 2) Stereum complicatum, 3) Stereum gausapatum (excluded by Chamuris(4) on the grounds that it is easily distinguished), 4) Stereum versicolor (Swartz: Fr.) Fr. (found in Florida and other tropical / subtropical areas), 5) Stereum styracifluum (Schwein.: Fr.) Fr. reported from Alabama and North Carolina, said to be effused or slightly reflexed and bleed yellow, regarded by Chamuris as a synonym of S. hirsutum, and 6) Stereum subtomentosum Pouzar, reported from Northwest Territories, Ontario, and Quebec, said to be effused-reflexed to stemmed and bleed yellow, regarded by Chamuris as a synonym of S. hirsutum, but suspected by Ginns(5) to be a common species, with specimens being misnamed S. ostrea. |The distinctions are sometimes not easy in practice - Welden(4) in 1971 despaired of differentiating Stereum complicatum and Stereum gausapatum from Stereum hirsutum because they were little different microscopically and morphological features were not dependable. Welden''s solution was to synonymize the other five taxa in the complex with Stereum hirsutum.

Microscopic:
SPORES 5.5-6.5 x 2-3 microns, elliptic-cylindric, smooth, weak amyloid reaction, colorless; BASIDIA 4-spored, 30-45 x 3.5-4.5 microns, narrowly clavate, without basal clamp connection; CYSTIDIA none, but cystidia-like ends of the skeletal hyphae "thick-walled, tips obtuse, 4-5 microns across (conducting hyphae)"; HYPHAE dimitic, 1) generative hyphae 2-3 microns wide, thin-walled to thick-walled, without clamp connections, 2) skeletal hyphae 3-5 microns wide, thick-walled, (Breitenbach) |SPORES 5-8 x 2-4(3.5) [sic] microns, narrowly elliptic to cylindric, smooth, amyloid, thin-walled; BASIDIA 4-spored, 25-60 x 3-5 microns, elongated-clavate; CYSTIDIA of 2 types: 1) pseudocystidia "abundant, arising from the trama and forming a fairly dense layer next to the hymenium, not or rarely projecting", 7-10 microns wide and often more than 100 microns long, thick-walled except for the apical part, sometimes with "a schizopapillae" [sic], the cystidium "in the upper part filled with an oily content", [illustrated more or less cylindric], 2) acutocystidia [sharp-tipped hyphidia] numerous, 20-30 x 2-4 microns, projecting slightly "and easily observed in a thin section"; HYPHAE monomitic, simple-septate, of 2 types, "in the hymenium thin-walled to slightly thick-walled and frequently branched, in the trama thick-walled, less branched, generally 4-6 microns wide, in the cortex yellowish-brown and thick-walled, in the tomentum thick-walled and with numerous adventitious septa, often 5-8 microns wide"; hymenium may be two-layered, (Eriksson)

Notes:
Stereum hirsutum is found in BC, WA, OR, ID, and also AB, NB, NF, NS, NT, ON, PE, PQ, SK, AK, AL, AR, AZ, CA, CO, CT, DC, FL, GA, IA, IN, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, NH, NJ, NM, NY, OH, OK, PA RI, SC, SD, TN, TX, VA, VT, WI, WV, and WY, (Ginns(5) who recognize the members of the complex as independent species). Stereum hirsutum is common in Scandinavia (Eriksson), and found in Europe including Switzerland, and in Asia, (Breitenbach). It is also found in Mexico, Ecuador, Germany, Italy, Malawi, Uganda, and the Philippines, (Chamuris(4)).

Synonyms and Alternate Names:
Phlebia mellea Overh.
Phlebia subalbida W.B. Cooke