Apothecia: arising singly, scattered over the upper surface of the host, 0.5-0.8 mm high stalk: unbranched, 0.04-0.07 mm thick, pale, dull, olivaceous brown; hyphae: periclinally arranged; outermost part: pale brown, with cells 2-3 times as long as broad, 4-5 µm thick, forming a thin cortex that continues upwards to form the exciple; inner part: pale, 2-3 µm thick capitulum: black, obconical, 0.09-0.16 mm in diam.; hypothecium: pale asci: narrowly cylindrical, when mature 80-98 x 3.5-4.5 µm; apical wall: thickened in young asci and penetrated by a narrow canal that widens during maturation, with uniseriate spores ascospores: simple to finally 1-septate, pale brown, quite variable in shape (ellipsoid, broadly to narrowly ellipsoid), 11-14 x 3-4 µm, with a thin septum Spot tests: all parts of the apothecia K-, N- Secondary metabolites: none detected. Substrate and ecology: on fruit-bodies of Trametes versicolor and Trichaptum biformis, usually on the upper side, that is often heavily colonized by algae World distribution: Europe, Siberia, and common in eastern U.S.A. Sonoran distribution: Arizona. Notes: The very pale brown spores distinguish P. polyporaeum from other species of Phaeocalicium. The apothecia are quite variable in shape; often the apothecia are quite small and the capitulum very narrowly obconical, just slightly larger in diameter than the stalk, but sometimes the capitulum is lenticular and three to four times the diameter of the stalk.