Summary:
Features include 1) growth on gills of Lactarius species, 2) color that is white to lemon yellow when fresh, buff, yellowish orange, tawny, at full maturity becoming ochraceous, brick red and brown or reddish black, the surface pimpled from perithecia, 3) a whitish cottony anamorph Acremonium tulasnei G.R.W. Arnold that may be found on host''s mummified fruitbody before perithecia or in early stages, 4) ascospores that are 1-celled (appearing 2-celled), mostly 15-21 x 3.6-4.8 microns, fusiform, lanceolate, or boat-shaped, with warts less than 0.5 microns high, and with a conspicuous acute apiculus. Rogerson(3) say that it is a variable species that may ultimately prove to be a complex of species: for instance, collections on Lactarius camphoratus complex "tend to have a yellowish subiculum and slightly larger ascospores".

Microscopic:
SPORES (11.2)15-21(30) x (2.6)3.6-4.8(6.0) microns, fusiform, lanceolate or naviculate, verrucose, verrucae < 0.5 microns high, apiculi (0.5)1.7-2.9(4.2) microns long and acute, spores one-celled "but with inclusions giving the appearance of a median septum"; ASCUS 90-150 x 4-8 microns, long cylindric, "apex thickened and with a pore"; PERITHECIUM 300-470 x 170-360 microns, ovate to obpyriform, "dark amber to reddish brown, becoming lighter and yellowish in KOH, immersed in the subiculum or half free, KOH-", papilla "120-150 microns high, 100-175 microns wide at apex", perithecial wall "15-30 microns wide, cells fusiform to sinuous, 7-15 microns long, 3-6 microns wide, walls 1.0-1.5 microns thick, nonpigmented", cells of papilla "with long axis parallel to long axis of perithecium and tending to be arranged in files, 7-15 microns long, 3-5 microns wide, walls 0.5-1.0 micron thick", "cells around the ostiolar opening tending to be narrowly clavate, 3 microns wide, merging the periphyses, cells of the papilla continuous with subicular hyphae at the surface, ostiolar canal periphysate"; subicular hyphae 2-5 microns wide, septate, much branched, "densely compacted but remaining filamentous and with many free ends at subicular surface" and sometimes forming enlarged terminal or intercalary, spherical to ellipsoid cells 18-25 x 7-9 microns, KOH-, (Rogerson), SPORES (15)21-27(30) x (3)4-5.5(6) microns, fusiform, aseptate, wall finely verrucose, verrucae 0.5 microns high, spore ends apiculate, apiculi 1.5-3(4) microns long with acute tips; ASCUS 90-150 x 4-8 microns, "with apex thickened, penetrated by a pore"; PERITHECIA formed all over the subiculum on host gills, "caespitose, immersed in the subiculum except the papilla", 300-470 x 170-360 microns, "buff to brown, KOH reaction with the whole perithecium turning yellow", perithecial wall 15-30 microns wide, perithecial papillae "120-150 microns high, 100-175 microns wide at the top, tip obtuse, of pseudoparenchymatous texture, with cells in divergent files, becoming narrower toward the ostiolar canal and more rounded towards the outer surface", cells at the surface 3 microns in diameter; SUBICULUM "profuse, buff or ochraceous", not changing color in KOH, texture hyphal, hyphae densely compacted, cells 2-5 microns wide, becoming swollen; CONIDIA (4.5)5-6.5(7.5) x 4.5-6(7) microns, round or nearly round, equilateral, "with no hilum or a minute central basal hilum", aseptate; conidiogenous locus with no proliferation observed, forming up to 6 conidia that are held in heads; conidiogenous cells (15)27-37(45) microns long, 2.5-3.2 microns wide at base, by 1-4(6) in a verticil, "often placed at right angle with respect to the conidiophore", proliferation not observed, forming 1 conidiogenous locus; CONIDIOPHORES "hardly or not differentiated from aerial hyphae, unbranched or branching verticillate or irregular", (Poldmaa)

Notes:
The distribution includes BC, WA, OR, ID, NS, ON, PQ, AK, AL, CA, CO, CT, IA, MA, ME, MD, MI, MN, MT, NC, NH, NJ, NM, NY, OH, PA, RI, SC, TN, VT, VA, WI, WY, Mexico, Austria, Belgium, Czechoslovakia, Denmark, Finland, France, Germany, Italy, Russia, Sweden, United Kingdom, and New Zealand: it occurs apparently worldwide wherever species of Lactarius occur, (Rogerson). It also occurs in Estonia, Ukraine, Kazakhstan, and Kyrgyzstan, (Poldmaa).