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DescriptionThallus: endosubstratic, non-lichenized; Apothecia: 0.5-0.6 mm tall, dark brown to black, epruinose; stalk: 0.04-0.06 mm in diam., olivaceous brown, occasionally forked; hyphae: periclinally arranged, brown throughout, slightly intertwined, 2-3 µm in diam.; capitulum: cup-shaped to obconical, not flattened; exciple: brown, formed by 6-9 layers of periclinallly arranged, hyaline (in the inner part) to sclerotized hyphae; hypothecium: hyaline to brown, consisting of periclinally arranged, thin-walled, short-celled hyphae; asci: cylindrical, 8-spored, 75-95 x 4-5 µm, strongly but uniformly thickened at the apex, with uniseriate spores; ascospores: predominantly 1-septate to rarely 3-septate, elliptical to elongate, brown when mature, 1318 x 5-7 µm; surface: papillate to areolate (but appearing smooth under light microscope), subtly to conspicuously constricted at septa; larger spores with cracks; Pycnidia: not seen; Spot tests: all parts of the apothecia K-, N-; stalk K-, N-; Secondary metabolites: none detected.; Substrate and ecology: on bark near the base of dead main stem of a Rhus; World distribution: boreal and north temperate zones of North America; Sonoran distribution: southern California.; Notes: Phaeocalicium curtisii is extremely similar to P. populneum, but differs in having a K- stalk, in the anatomy of the stalk (P. curtisii lacking a layer of hyaline, swollen hyphae at the surface) and in having Rhus rather than Populus as host.