Distinctive field characters are the large irregular pores and the black layer separating the upper tomentum from the lower flesh. These together distinguish it from other Datronia spp. in the Pacific Northwest. Other features include a usually shelf-like form, a dark brown concentrically grooved upper surface, and a pore surface that is buff to umber brown with angular to maze-like pores.
Datronia mollis has been found in BC, WA, OR, ID, NS, ON, PQ, AK, CO, IA, IL, IN, KY, ME, MI, MN, MT, NH, NY, OH, PA, TN, VA, VT, WI, WV, and WY, (Gilbertson).
usually bent out to form cap from part of the fruitbody that is flat on wood with pore-surface exposed, occasionally shelf-like or entirely flat on the wood, cap up to 2cm broad, annual; upper surface dark brown to black; strigose to bald, concentrically zoned and grooved, (Gilbertson), up to 7cm wide, 2.5cm broad, 0.6cm thick, shelf-like brackets often in tiers, wavy, thin but tough and leathery; upper surface umber brown becoming darker brown to black; velvety then smooth, (Phillips), bound +/- loosely to wood, when shelf-like projecting up to 1.5cm from wood, (Breitenbach)
lower layer pale buff, up to 0.1cm thick, "separated from dark brown upper layer of tomentum by a thin black layer", (Gilbertson), up to 0.1cm thick, lower layer pale buff, upper layer dark brown, separated by thin black layer, (Phillips), leathery and tough when fresh, hard and brittle when dry, use hand lens to see black line between flesh and tube layer, (Breitenbach)
1-2 per mm, some over 1mm wide, pore shape angular to maze-like, walls becoming thin and splitting; buff to umber brown; tube layer up to 0.3cm thick, colored as lower flesh, (Gilbertson), 1-2 per mm, angular, irregularly elongate or slot-like; buff to umber brown; tube layer up to 0.3cm thick, pale buff, (Phillips), gray-brownish to ocher-brownish, discoloring somewhat brown when bruised, (Breitenbach)
spores 10-12 x 3-4.5 microns, cylindric, smooth, inamyloid, colorless; basidia 4-spored, 30-45 x 5-6.5 microns, clavate, with a narrow base, with basal clamp; cystidioles imbedded or slightly projecting, 25-45 x 4-5 microns, fusoid, thin-walled, with basal clamp, dendrohyphidia present on dissepiment edges, 1.5-3 microns wide, branched and contorted; hyphal system dimitic: context generative hyphae 2.5-4 microns wide, thin-walled, nodose-septate, context skeletal hyphae "thick-walled, aseptate, those in lower context pale greenish-brown in KOH, those in upper dark layer darker brown in KOH, some with frequent branching, 2.5-4 microns in diam", trama hyphae similar to those in lower context, (Gilbertson), spores 8-10.5 x 3.5-4 microns, cylindric-elliptic, smooth, inamyloid, colorless, some with drops, (Breitenbach)