Summary:
Features include 1) effused growth on wood and other substrates, 2) a yellow brown surface that develops low ridges forming a reticulum, then conic spines that are olive-yellow, yellow, or brownish, when fresh bruising red-brown, 3) a margin that is whitish to honey-yellow to brownish yellow, typically matted-cottony, 4) hyphal strands that are common to rare, microscopically composed of few to several wide core hyphae surrounded by narrow, branched hyphae, 5) spores that are broadly elliptic, smooth, (usually) weakly dextrinoid, yellow, cyanophilic, and with a wall about 0.8 microns thick, 6) cystidioles that are thin-walled and mostly clavate, and 7) numerous to rare black sclerotia.

Microscopic:
SPORES (4.8)5-6(7) x 3.6-4.4(4.8) microns, broadly elliptic, some broadly oval to nearly round, "the adaxial surface slightly to distinctly flattened", smooth, usually weakly dextrinoid ("but sometimes only the walls of a few spores becoming red-brown"), pale yellow to yellow, cyanophilic, wall about 0.8 microns thick; BASIDIA 4-spored, 20-38 x 6-7.6 microns, clavate to narrowly clavate, sterigmata nearly 5 microns long; CYSTIDIOLES numerous, colorless, thin-walled, occasionally projecting 5(10) microns, usually clavate or narrowly clavate, 4-7 microns wide, "some narrower ones with apices irregularly inflated, forked, or crooked, or with finger-like extensions"; SUBHYMENIUM about 50-70 microns thick, the hyphae 2-4 microns wide, rather loosely woven, much branched, short-celled, staining with difficulty and may be embedded in a gelatinous matrix, with clamp connections; TRAMAL HYPHAE 5-8(12) microns wide, "closely packed, parallel, forming a distinct core in the larger ridges and teeth", colorless, thin-walled, clamp connections scattered and inconspicuous, branches of 2 types: 1) "to hyphae of comparable diameter, these uncommon, arising at an acute angle from the parent hypha and near a septum", and 2) to very narrow hyphae (2-4 microns wide), "arising from hyphae on the exterior of tramal core and giving rise to the subhymenium"; CONTEXT HYPHAE 3-8 microns wide, woven, colorless "or some next to the substrate with pale yellow to brownish walls", thin-walled, with frequent clamp connections; HYPHAL STRANDS up to 150 microns wide, composed of few to several wide (6-12 microns wide) core hyphae that are surrounded by numerous, narrow (3-5 microns wide), branched hyphae, (Ginns(15))

Notes:
Collections were examined from BC, WA, ID, ON, PQ, CA, NC, NY, OH, PA, SC, WI, Puerto Rico, Belgium, Denmark, Finland, Sweden, United Kingdom, Uganda, and New Zealand, (Ginns(15)), Hydnomerulius pinastri has also been recorded from OR, AK, AR, AZ, CO, DC, FL, IA, IL, IN, KY, LA, MA, MD, ME, MI, MO, MT, NE, NH, NM, TN, VA, VT, and WV, (Ginns(5)).

Synonyms and Alternate Names:
Irpiciporus lacteus (Fr.) Murrill
Sistotrema lacteum Fr.