Summary:
Features include 1) growth on Russula species and occasionally Lactarius, covering deformed gills and often the stem, sometimes the cap, turning the fruitbody firm, 2) color that is yellow or green, 3) large unicellular spores, 4) a peculiar anatomy of the perithecial apex ("distinctive for the moniliform chains of cells that extend from the surface of the papilla"), and 5) no anamorph known in nature. It should not be eaten (Lincoff). It is common in wet weather wherever the host species are found, throughout many parts of North America, (Phillips).

Microscopic:
SPORES 32-35 x 4.5-5.5 microns, fusiform to naviculate, nearly smooth to prominently verrucose and apiculate (verrucae up to 1 micron high, "apiculi 2.4-7.3 microns long, acute, straight or curved and sometimes hooked"), one-celled; ASCUS 160-200 x 5-8 microns, filiform to long cylindric, "apex thickened and with a pore"; PERITHECIUM 380-485 x 180-290 microns, broadly ovate to obpyriform, immersed except for papilla, papilla 96-120 microns high, 180-230 microns wide at apex, truncate or obtuse, KOH-, perithecial wall about 25 microns wide laterally, of hyphae 3-4 microns wide, sinuous, with nonpigmented walls, perithecial apex composed "of hyphae constricted at septa and appearing moniliform with cells 5-7 microns long, 4-5 microns wide" and walls < 0.5 microns thick, "hyphae tending to separate from each other"; subicular hyphae 3-5.5 microns wide, "much branched, septate, much entangled, remaining filamentous", "hyphae at the surface with many 3 microns wide free ends and short cells with constrictions at the septa" and mimicking the hyphae of the perithecial apex, KOH-, (Rogerson), SPORES (27)30-36 x 4.5-5.5(6.5) microns, fusiform, aseptate, "finely verrucose, verrucae arranged uniformly, 1 micron high, ends apiculate", apiculi 2.5-7 microns long, with acute tips; ASCUS 160-200 x 5-8 microns, "with apex thickened, penetrated by a pore"; PERITHECIUM 380-480 x 180-290 microns, "immersed in the subiculum except the papilla", perithecial wall 25 microns wide, perithecial papillae 95-120 microns high, tip obtuse, "of hyphal texture, with cells not forming differentiated regions"; subiculum cells 3-5.5 microns wide, not swollen; anamorph in nature not observed, (Poldmaa)

Notes:
It is widespread in north temperate regions, occurring in BC, WA, OR, ID, AB, MB, NB, NS, PQ, AK, AZ, CO, CT, FL, GA, OH, MA, MD, ME, MI, MT, NC, NH, NJ, NM, NY, OH, PA, RI, SC, TN, TX, UT, VA, VT, WI, WV, Czechoslovakia, Denmark, Estonia, France, Finland, Germany, Norway, Russia, Spain, Sweden, Switzerland, United Kingdom, and Japan, (Rogerson). It also occurs CA (Castellano) and in Ukraine and Kazakhstan, (Poldmaa).