Summary:
Features include 1) resupinate growth on rotten wood on the ground, 2) a fruitbody that is white, cottony, soft, thin, membranous, smooth, and fringed with fine white rhizomorphs, 3) spores that are nearly round to elliptic, smooth, white to yellowish, non-amyloid, and thick-walled, 4) a monomitic hyphal system, the hyphae without clamp connections, usually with attached needle-like crystals.

Microscopic:
SPORES 3-4.5(5) x 2.5-3.5(4) microns, broadly elliptic, smooth, inamyloid, colorless, rather thick-walled, with one droplet; BASIDIA 4-spored, 10-22 x 4-6 microns, somewhat stemmed, clavate, without basal clamp connection; CYSTIDIA not seen; HYPHAE monomitic, without clamp connections, subhymenial hyphae 2-3 microns wide, thin-walled, smooth, basal hyphae 2.5-4 microns wide, thin-walled to thick-walled, "strongly incrusted with needle-shaped crystals" that do not turn yellow in Melzer''s reagent, (Breitenbach), SPORES 3-4(4.5) x 2.5-3.5 microns, nearly round to elliptic, smooth, with thickened walls, white to yellowish, in Melzer''s reagent not amyloid but yellow or in mass in some fruitbodies yellow-brown; BASIDIA (2-)4-spored, (10)12-15(25) x 3.5-5 microns, clavate, sometimes with yellow contents, basal part often prolonged, without basal clamp connection; CYSTIDIA none; HYPHAE monomitic, 2.5-3.5 microns wide, without clamp connections; in the subhymenial layer richly branched, thin-walled, as a rule covered with crystals; in the basal layer hyphae "with thin to thickened walls, normally with small, attached, baculiform crystals" but lacking yellow encrustation in Melzer''s reagent, (in many specimens the basal hyphae may have, instead of KOH-crystals, an amorphous grainy encrustation dissolved in Melzer''s reagent), (Eriksson)

Notes:
Piloderma byssinum has been found in BC, WA, OR, ID, AB, NS, ON, AZ, CO, IL, MA, MN, MT, ND, NM, NY, UT, and WY, (Ginns). It has also been found in Austria, Czechoslovakia, Denmark, Finland, France, Germany, Norway, Sweden, United Kingdom, USSR, and Morocco, (Julich).