Summary:
Features include a cinnamon to ochraceous sappy fruitbody with a violet reaction to KOH, growing shelf-like or bent outward from a flat pore surface on wood. The description is derived from Gilbertson(1) except where noted. It is common in the eastern United States and in the southwest, but rare elsewhere in western North America (Gilbertson).

Chemical Reactions:
all parts of fruitbody with light violet to purplish reaction to KOH

Odor:
sweetish (Phillips)

Taste:
mild (Breitenbach)

Microscopic:
spores 3.5-5 x 2-2.5(3) microns, elliptic to cylindric, smooth, inamyloid, colorless, thin-walled; basidia 4-spored, 18-22 x 5-6.5 microns, clavate, with basal clamp; cystidia none but cystidioles present, 18-22 x 4-5 microns, fusoid, with basal clamp; hyphal system monomitic: context generative hyphae up to 10 microns wide, "distinctly thick walled and richly branched, mostly smooth, but also covered partly with amorphus [sic] substances mixed with polygonal, light pinkish to brownish crystals", with conspicuous clamp connections, in trama and hymenium up to 6 microns wide, more straight and narrow

Spore Deposit:
white (Lincoff, Phillips)

Notes:
Hapalopilus nidulans has been found in BC, WA, ID, MB, NWT, NB, NS, ON, PQ, AZ, CT, DE, IA, IL, IN, KS, LA, MA, MD, MI, MN, MO, NC, NH, NJ, NM, NY, OH, PA, TN, VA, VT, WI, and WV, and it occurs circumglobally in the temperate zone, (Gilbertson(1)).

Synonyms and Alternate Names:
Hapalopilus rutilans (Pers.: Fr.) P. Karst.
Polyporus nidulans Fr.
Polyporus pallidocervinus Schwein.
Polyporus rutilans Fr.