Summary:
Features include 1) resupinate growth on wood, 2) a reddish gray to violet-gray or blue-gray fruitbody, waxy and tough, smooth, with an abrupt margin, often with a narrow darker zone, 3) spores that are cylindric, slightly curved, smooth, and colorless, 4) a reddish spore print, 5) cystidia of two types: a) encrusted, conic, thick-walled cystidia, and b) thin-walled sulfocystidia, and 6) a monomitic hyphal system, the hyphae with clamp connections, the subhymenial hyphae vertically arranged, contrasting against the darker horizontally arranged subicular hyphae.

Microscopic:
SPORES 5.5-7 x 2.5-3 microns, cylindric, slightly allantoid, smooth, inamyloid, colorless, some with droplets; BASIDIA 4-spored, 25-45 x 4.5-5 microns, narrowly clavate, with basal clamp connection; CYSTIDIA: 1) lamprocystidia thick-walled, brownish, encrusted part 20-25 x 10-15 microns, total length up to 60 microns, some projecting, 2) sulfo-positive gloeocystidia 50-70 x 7.5-10 microns; HYPHAE monomitic, 2-4.5 microns wide, colorless to brown, thin-walled to thick-walled, septa with clamp connections, (Breitenbach), SPORES (6)6.5-7.5(9) x 2.5-3 microns, allantoid, smooth, colorless, thin-walled, reddish in spore print, it is noted that the "spore size 5.5-6.5 microns given by Eriksson 1950 is true mainly for N. Sweden"; BASIDIA 4-spored, 30-40 x 5-7 microns, subcylindric or subclavate, sometimes constricted or sinuous, with basal clamp connection; CYSTIDIA numerous, of 2 types, 1) encrusted, 35-65 x 12-15 microns, encrusted part 25-35 microns long, cystidia generally conic, at first thin-walled and colorless, "then apically encrusted and at least in basal part brown", those of the first hymenial layer largest and basally brown, later cystidia smaller and more or less colorless, 2) sulfocystidia, 50-70(100) x 8-10 microns, oblong to subcylindric, "as a rule obtuse, with thin or basally thickened walls", "contents continuous, granular, or with oily droplets, aldehyde reaction weak in many herbarium specimens but strong at least in vividly growing ones", sulfocystidia not always found in old specimens; HYPHAE monomitic, with clamp connections, young ones thin-walled and colorless, old hyphae brown and more or less thick-walled; subhymenial layer "of dense, vertically arranged hyphae", colorless in young specimens, "more or less pigmented in older ones but as a rule sharply contrasting against the darker subiculum, subhymenium generally not stratified but in some specimens two or three layers visible"; "subiculum varying in thickness from an inconspicuous layer of horizontal hyphae to a considerable (up to 40 microns) thickness, composed of parallel, dense, dark brown hyphae", (Eriksson)

Notes:
Peniophora pithya has been found in BC, AB, NB, NS, ON, PQ, AZ, and UT, (Ginns), as well as in Switzerland, in Asia, (Breitenbach), and in Denmark, Finland, Norway, and Sweden, (Eriksson).