Summary:
Features include a disc-shaped to cup-like, brownish fruitbody, growth on hardwood especially birch, and microscopic characters. Klett(2) restricted Exidia repanda to the narrow spored form 11-15 x (2.5)3-4 microns examined from AK, Sweden, and Germany, and distributed "Probably throughout Alaska, northern Canada, and northern Europe", and had not seen any North American collections of the wider spored form (12-16.5 x 4-6 microns) which is supposed to occur sporadically in middle and western Europe.

Microscopic:
spores mostly 12-13 x 3-4 microns, allantoid [curved sausage-shaped]; probasidia 10-13(16) x 9-11(13) microns, ovate to nearly spherical, brownish, becoming cruciate-septate or sometimes merely 2-celled, epibasidia slender, 2-2.5 microns wide below the expanded tips, up to 50 microns long, (Martin), spores 8.5-17 x 2-4 microns, oblong-elliptic to reniform or allantoid, with broad (about 1 micron) apiculus, colorless, aseptate before germination, germination by conidial formation or germ tube; basidia in cymose clusters, probasidia 8-17 x 4.5-9.5 microns, at first subcylindric to clavate, becoming predominantly subspherical or obovate, some spherical or ellipsoid, with or without short stem, with basal clamp connections, 2-4-celled by longitudinal to slightly oblique septa, hypobasidia 9-17.5 x 6-10 microns, differentiating 2-4 segments, epibasidia cylindric, up to 45 microns long, 1-2.5 microns wide at broadest point, somewhat contorted; dikaryophyses forming a layer 35-65 microns thick above the basidial zone, "contorted, irregularly branched, and branches tapering toward the pointed apices", with basal clamp connections; hyphae 1-4 microns thick, thin-walled, with conspicuous clamp connections, (Aoki), spores 11-15 x (2.5)3-4 microns, cylindric-curved, colorless, white in mass, capable of germinating by repetition; basidia "arising as clavate structures subtended by clamp connections, proliferating through the clamp connections to form cymose clusters", probasidia becoming ellipsoid to obovate, then 10-15 x 7.5-10.5 microns, becoming 2-celled to 4-celled by longitudinal to slightly oblique septa, hypobasidia mostly ellipsoid, 11-15 x 8-11 microns, epibasidia 1.5-2.5 microns wide at bases; dikaryophyses with basal clamp connections, forming a layer 10-40 microns thick above the level of the basidia, mostly 2-3.5 microns wide toward bases, contorted, irregularly branched apically, with occasional ones cylindric, up to 5 microns wide, contorted, unbranched, or abruptly narrowed apically and branched; hyphae 1.5-3.5 microns wide, thin-walled, "with conspicuous clamp connections varying from closed to keyhole to looplike, occasionally spurred", (Klett)

Notes:
Exidia repanda has been reported from AK (Klett), WA, ID, ON, AL, LA, ME, MN, and NJ, (Ginns), and France, Germany, Poland, Sweden, USSR, and Japan, (Aoki). There is a BC collection from 1965 by J. Holms at the University of British Columbia and another BC collection from 1969 by Robert Gilbertson at the University of Arizona.

Synonyms and Alternate Names:
Parmastomyces transmutans (Overh.) Ryvarden & Gilb.