Summary:
Features include 1) resupinate growth on wood, 2) fruitbodies that are thin, whitish to yellowish to grayish, 3) smooth, amyloid, elliptic to cylindric spores (seen to advantage only scattered through the hymenial layer in Melzer''s reagent), 4) a catahymenium comprised of a) basidial elements (basidia rarely seen emergent), b) paraphysoids, c) variously shaped pseudocystidia, and d) bottlebrush-like acanthophyses that are filiform to subclavate, and 5) context that is monomitic with clamp connections. This is a collective species, with limits yet to be defined precisely, (Lemke).

Microscopic:
SPORES about 10 x 6 microns, elliptic to subcylindric, smooth, amyloid; BASIDIA 4-spored, about 40-50 x 7-8 microns; PSEUDOCYSTIDIA numerous, about the same size as basidia, variable in shape but usually with a more or less moniliform apex, contents colorless or slightly yellowish and finely granular; ACANTHOPHYSES numerous, with apical protuberances [giving a somewhat bottlebrush-like appearance]; HYPHAE monomitic with hyphae 2-4 microns wide, thin-walled, clamped, (Eriksson), SPORES inconspicuous in KOH and "may be seen to advantage only in Melzer''s, where they initially appear as embedded, often collapsed, amyloid fragments which tend to regain their shape after about 10 minutes", (7)8-10(11) x (4.5)5-6(7) microns, oval to oval-elliptic, slightly flattened adaxially, smooth, amyloid, thin-walled; catahymenium consisting of basidial elements, paraphysoids, variously shaped pseudocystidia, and filiform to subclavate acanthophyses; BASIDIA 4-spored, rarely seen emergent, 30-35 x 6-8(9) microns, sterigmata incurved, basidioles embedded, (25)35-50 x (5.5)6-8(9.5) microns, clavate; PARAPHYSOIDS 2-2.5 microns wide, filiform to singly branched in upper part; PSEUDOCYSTIDIA (macrocystidia) "variable, scattered to numerous, initially embedded as long flexuous-cylindric elements", 40-65(85) x (7)8-12(14) microns, "becoming emergent to the level of the hymenium, and then subclavate to fusiform", measuring (30)40-50 x (5.5)6-10(11) microns, apically moniliform, contents of pseudocystidia faintly yellowish in KOH; ACANTHOPHYSES thin-walled, subclavate to filiform, mostly subclavate, 30-40 x (4)5-7 microns, "aculeate to acicular-pronged at the apex", pronged parts thick-walled to semisolid, 4-6 microns wide, covering the upper quarter of the acanthophysis, also filiform acanthophyses, 2.5-3.5 microns wide, pronged at apices; HYPHAE monomitic, of hyphae 2-2.5 microns wide, "branched, subregular, thin-walled, clamped", BASAL HYPHAE reaching 3.5-4 microns wide, clamped, with partially thickened walls, (Lemke)

Notes:
Acanthophysium cerussatum has been recorded from BC, WA, OR, ID, AB, MB, ON, AZ, CO, FL, MN, NM, and SD, (Ginns). Collections were examined from BC, ID, MB, ON, FL, NM, Italy, France, and Austria, (Lemke).