E-Flora BC: Electronic Atlas of the Flora of British Columbia

Summary:
Features include 1) resupinate growth on hardwood of a firmly attached fruitbody that is whitish to ocher-brown color with a smooth to tuberculate surface, 2) oblong to suballantoid, smooth, amyloid spores, 3) basidia narrowing in the basal direction, 4) paraphysoid hyphae often between the basidia, 5) tubular gloeocystidia with granular, oily, yellowish contents, 6) a monomitic hyphal system, the hyphae with clamp connections, and 7) crystals in the trama of old fruitbodies. The name Megalocystidium leucoxanthum (Bres.) Julich is accepted by Ginns(24), but Stalpers(2) still called it Gloeocystidiellum leucoxanthum, as did the online Species Fungorum, accessed May 31, 2016.

Collections were examined from BC, WA, OR, ID, AB, MB, NB, NF, ON, YT, AK, AZ, CA, CO, MN, MT, NH, and WI, (Ginns(24)). It has been found in Europe including Denmark, Finland, Norway, Sweden, and central Europe, (Eriksson), and including France (Bourdot).

Fruiting body:
resupinate, adnate [tightly attached] or when old detachable in pieces, at first thin but thickening (up to 0.1cm), orbicular [circular] at first but soon becoming confluent; whitish to creamish pale, then melleo-ochraceous [honey-ochraceous] to isabel-colored [pale tan] or light ocher-brown; at first smooth but becoming uneven to conspicuously tuberculate and deeply rimose [cracked]; margin byssoid [cottony] when young, not especially differentiated when mature or old, (Eriksson), effused, up to 30cm x 5cm and up to 0.05cm thick, ceraceous [waxy], "pinkish buff", "cinnamon buff", to "clay color" when dry, "smooth to strongly tuberculate, not cracked or cracked extensively exposing the nearly white subiculum"; margin abrupt to slightly pruinose, whitish or colored as the rest of the surface, up to 0.1cm wide, (Ginns(24)), spore deposit white (Buczacki)

Microscopic:
SPORES 12-20 x 4.5-7 microns, oblong to suballantoid, adaxial side somewhat concave, smooth, amyloid, thin-walled; BASIDIA normally 4-spored, 40-60 x 6-8 microns, clavate, narrowing toward base, with basal clamp connection; paraphysoid hyphae frequently occurring between the basidia; GLOEOCYSTIDIA (= pseudocystidia) numerous, 100-150 x 8-15 microns, shorter when young, occasionally broader ones can be found, tubular, sinuose, contents granular, oily, yellowish in water and KOH, often with moniliform apical appendices; HYPHAE monomitic 2-3.5 microns wide, "with thin or somewhat thickened walls", with clamp connections, BASAL HYPHAE forming layer about 100 microns thick "of irregularly intertwined hyphal branches in a rather loose tissue, subhymenial trama denser; old fruitbodies with plenty of crystals in the trama context", (Eriksson), SPORES (12.8)15.2-17.6(21.0) x 4.5-7.0 microns, elliptic to suballantoid, smooth, amyloid, easily collapsed, with distinct, blunt apiculus; BASIDIA 4-spored, 45-65 x 5.0-7.5 microns, clavate, sterigmata up to 5.0 microns long; GLOEOCYSTIDIA numerous, 60-160 x 10-16 microns, "cylindric to subfusoid, some with constrictions and some with a bulb at the apex, the walls thin to 0.5 microns thick, the contents yellow in KOH, granular, sulfo-negative, but many appear to be empty"; HYPHIDIA scattered, 2-2.6 microns wide, filiform, simple, projecting up to 16 microns; HYPHAE monomitic, 2.5-5.0(5.5) microns wide, "with clamp connections, the walls thin, distinct, forming a loosely interwoven to compact, distinct, parallel layer about 50-100 microns thick next to substrate"; marginal hyphae weakly amyloid en masse; gloeoplerous hyphae in margin, (Ginns(24))