Summary: Features include flat growth tightly attached to conifer wood with the pore surface exposed, cream pore surface that darkens to yellow or orange, and microscopic characters including small cylindric to slightly curved spores that measure 4-5 x 1.5-2 microns, heavily incrusted thick-walled cystidia, and hyphal pegs; The online Species Fungorum, accessed September 4, 2018, gave the current name as Butyrea luteoalba (P. Karst.) Miettinen, in Miettinen & Ryvarden, Ann. bot. fenn.: 161 (2016), but MycoBank, accessed the same day, gave that name as a synonym of Junghuhnia luteoalba (P. Karst.) Ryvarden.
Microscopic: spores 4-5 x 1.5-2 microns, cylindric, straight to slightly curved, smooth, inamyloid, colorless; basidia 4-spored, 13-20 x 4-5.5 microns, clavate, with a basal clamp; cystidia abundant to infrequent, completely imbedded to projecting to 30 microns, 40-70 x 9-14 microns, clavate to fusoid, thick-walled, heavily incrusted, "usually most abundant near dissepiment edges and originating from subhymenial tramal skeletal hyphae", cystidioles also present, 13-27 x 4-5 microns, fusoid, thin-walled, with basal clamp, hyphal pegs usually abundant (ridges or fascicles of sterile hyphae that appear as peg-like projections in cross-sections of tubes); hyphal system dimitic, subicular generative hyphae 2-4 microns wide, thin-walled, rarely branched, with clamp connections, subicular skeletal hyphae 2-4 microns wide, colorless, thick-walled, nonseptate, rarely branched, trama hyphae similar, (Gilbertson), spores 5-6.5(7) x 1.8-2.3(2.5) microns, cylindric, allantoid, smooth, inamyloid, colorless, with droplets; cystidia embedded in hymenium, up to 100 x 7-15 microns, thick-walled, "with coarse, dense incrustation on the upper part", (Breitenbach)
Notes: Junghuhnia luteoalba has been found in BC, OR, ID, AB, NF, ON, PQ, AZ, CO, FL, GA, LA, MA, MD, MN, MT, NC, NH, NY, PA, TN, VA, VT, and WI, (Gilbertson), and Europe and Asia (Breitenbach).
Habitat and Range
SIMILAR SPECIES
Irpex lacteus when young can look somewhat similar, but lacks clamp connections, (Breitenbach).
Habitat
annual, on dead wood of conifers, causes white pitted and laminated rot of dead conifer wood, (Gilbertson), on the underside of dead conifer wood, (Breitenbach)