Summary:
Crustoderma longicystidiatum is a rare fungus identified in North America only as cultured from unseasoned conifer lumber, and from about 5 collections on coniferous wood in Europe: features include 1) a resupinate, closely attached, soft-waxy fruitbody colored ash-gray to brownish gray with smooth surface that is velvety under a lens, 2) spores measuring 6-9 x 4-5 microns, and 3) cylindric cystidia that are 100 microns or more long and thick-walled in their lower part.

Microscopic:
SPORES 6-9 x 4-5 microns, elliptic-oblong, smooth, inamyloid, acyanophilic, with 1 large oil droplet or 2 or more smaller ones; BASIDIA 4-spored, 20-30 x 5-6 microns, narrowly clavate, with basal clamp connection; CYSTIDIA numerous, 100 microns or more long (according to Litschauer up to 370 microns), 7-12 microns wide, cylindric, obtuse, thin-walled in apical part, thick-walled toward base, "in old cystidia walls swelling in KOH, more or less encrusted with crystals or resinous matter"; HYPHAE monomitic with clamp connections, hyphae in subhymenium 2-3 microns wide, thin-walled, densely conglutinate, BASAL HYPHAE 3-4 microns wide, with thin to somewhat thickened walls, "next to the wood a thin layer of horizontal hyphae", "old tissue containing a yellowish, resinous encrustation"; chlamydospores "in multitude in the type specimen, formed in the end of vertical hyphae in the hymenium", "at first rounded, claviform or fusiform and finally loosening, then rounded or angular, thick-walled, with one or more oildrops", young chlamydospores gray in Melzer''s reagent, mature ones 12-15 x 7-10 microns, (Eriksson), BASIDIOSPORES 6-9 x 4-5(6) microns, elliptic to broadly cylindric, slightly thick-walled; CYSTIDIA 100-160(200) x 10-14 microns, lightly encrusted with resinous or crystalline material; type specimen has numerous slightly thick-walled cystidioles, also referred to as chlamydospores in Eriksson(6) or paraphyses (by Litschauer in 1928) in the hymenium and rather small BASIDIA (20-30 microns long), the cystidioles are rare and have only been observed in one other specimen (Nakasone), SPORES 6.4-8.0 x 4.0-4.6 microns, elliptic, some nearly cylindric, with broadly rounded apices, smooth, inamyloid, colorless, thin-walled; BASIDIA 4-spored, 50 x 7-8 microns, narrowly clavate; HYPHIDIA scattered in the hymenium, 2.5-3 microns wide, filiform; CYSTIDIA common, projecting through the hymenium, about 140 x 10 microns, cylindric with obtusely rounded apex, smooth, colorless, walls thickened over the basal two thirds "and in some staining weakly blue-gray in Melzer''s reagent"; SUBHYMENIAL HYPHAE 2-5 microns wide, vertically oriented, much branched, short-celled, with single clamp connections; SUBICULAR HYPHAE 3-4 microns wide, loosely woven, colorless, walls irregularly thickened, a single clamp connection at each septum; chlamydospores scattered in the subiculum, mostly round, generally about 9 microns in diameter but a few up to 15 microns in diameter, "the walls thick, smooth, in Melzer''s reagent swelling slightly and staining weakly to moderately intense blue-grey", (Ginns(13)), SPORES 7-8 x 4-5 microns (variable), elliptic, inamyloid, slightly thick-walled; BASIDIA normally more than 20 microns long, more or less clavate with tapering base, 4-spored; CYSTIDIA cylindric, "with thickened walls, terminal and usually 90-120 x 8-9 microns, sometimes up to 200 microns or more and 10-12 microns wide", sulfo-negative, inamyloid; HYPHAE monomitic, about 4 microns wide, subhymenial hyphae thin-walled or with slightly thickened walls, subicular hyphae distinctly differentiated, thick-walled, and irregular, (Hjortstam)

Notes:
Crustoderma longicystidiatum was cultured from unseasoned lumber in BC (Ginns(5)). It has been found in Austria, and Norway, (Nakasone), and Finland, (Eriksson).

Synonyms and Alternate Names:
Hypoxylon mammatum (Wahlenb.) P. Karst.
Sphaeria mammata Wahlenb. 39 1879