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

Summary:
Features include 1) resupinate growth on wood, 2) a fruitbody that is thin, chalk-white to ochraceous, the older specimens usually with abrupt margins and a tuberculate surface, 3) cylindric-curved spores, 4) obovate basidia that are longitudinally septate, 5) two types of dikaryophyses, 6) clamp connections, and 7) mineral crystals especially in the vicinity of the hymenium.

Exidiopsis macrospora has been found in BC, NS, ON, CO, FL, IA, OH, MO, NH, NY, TN, TX, and WI, (Ginns), as well as Europe (Wells).

Fruiting body:
leathery, dry, "at first very thin, whitish to pale drab or dingy ochraceous, orbicular, appressed, with a cottony, concolorous or white margin, becoming broadly expanded by growth and confluence, up to 10cm or more in extent and much thicker, with determinate, reflexed, often subapplanate margins, hymenium at first smooth, then developing scattered, forked or branching spines and tubercles on the surface, ochraceous or brownish, finally shining white when dry, usually with ochraceous or pinkish brown patches", (Martin), thin at first, (0.0025)0.006-0.03(0.055)cm thick in section, in scattered patches, coriaceous [leathery], dry, with adnate [firmly attached], fimbriate [fringed] margins, becoming confluent, thicker, and with abrupt margins that may become reflexed [curl back] with drying; "at first pale drab or ochraceous, becoming white with ochraceous patches to chalk-white", dries to ochraceous to shining white layer; at first smooth, often finely pruinose at low magnification, becoming scattered-tuberculate, (Wells)

Microscopic:
SPORES 10-15(17) x 5-7(8) microns, suballantoid to ovate; PROBASIDIA 18-22 x 10-12 microns, ovate, often becoming nearly spherical, eventually cruciate-septate or sometimes 2-celled, epibasidia up to 20 microns or more long, 2-3.5 microns wide, coarse; "slender, tortuous, sparsely branched paraphyses, together with clavate and often septate paraphyses arising from the same hyphae as the basidia and with a clamp-connection at the septum, the tips of the slender paraphyses forming an agglutinated layer 20-40 microns thick above the basidia"; in section, very thin to 300(450) microns thick, consisting of a horizontal layer of interwoven hyphae parallel with the substrate, (at first colorless, then brown), an intermediate layer of gelatinized hyphae, (often calcareous), and a rather wide hymenial zone of closely aggregated basidia and paraphyses, (Martin), SPORES 10-15(17) x 5-7.5(8) microns, usually cylindric-curved, guttulate, "germinating by formation of germination tube or by repetition"; hymenium consists of fertile hyphae and two types of dikaryophyses: fertile hyphae 2-5 microns wide, toruloid, forming basidia in clusters by lateral proliferation through or near subbasidial clamp connections, probasidia arising as elongate structures becoming ovate, obovate or almost subspherical with 2 or 4 longitudinal septa, guttulate, 15-22 x 8-14 microns, epibasidia 2-4(5) microns wide, up to 75 microns long; DIKARYOPHYSES of two types: a) slender ones 1.5-4(5) microns wide, "simple to little branched, usually nodulose, becoming indistinct", forming a well defined layer 20-75 microns thick above the mature basidia, b) subcylindric septate dikaryophyses 35-70 x 3.5-10 microns, cylindric (or sometimes clavate or subfusiform), flexuous [wavy], colorless, apparently arising from the fertile hyphae; basal layer of hyphae 2.5-4 microns wide, becoming yellowish and somewhat thick-walled, with clamp connections, either parallel with substrate or interwoven and ascending, superficial to that an ascending interwoven layer of indistinct toruloid hyphae 2.5-4(6) microns wide, with clamp connections, terminating in the hymenium; mineral granules usually abundant throughout, often very abundant in vicinity of hymenium, (Wells)