Apothecia: sessile or subsessile, 0.13-2 mm in diam., 0.16-0.24 mm high mazaedium: greenish, not higher than the width of the capitulum; paraphyses: sclerotized, persistent exciple: in section reddish brown, turning deeper brown with K and slowly turning yellowish green with N asci: when mature, ellipsoid, 8.9-11.1 x 2.8-3.4 µm ascospores: aeruginose, when mature 1-septate, ellipsoid, 8.9-11.1 x 2.8-3.4 µm; with a distinct ornamentation of spirally arranged ridges Pycnidia: 0.04-0.6 mm in diam.; walls: reddish brown conidia: narrowly ellipsoid, 2-3 x 1 µm, formed from phialides Spot tests: exciple K+ dark reddish brown, N+ yellowish brown or aeruginose in part; spores K+ yellowish brown, N+ aeruginose; pycnidial wall K+ aeruginose, N+ dark reddish brown. Substrate and ecology: on species of calicioid lichens (e.g., Calicium viride and Chaenotheca subroscida) World distribution: South America, Australia and North America Sonoran distribution: California. Notes: Microcalicium conversum resembles M. disseminatum in having sessile or subsessile apothecia, sclerotized and persistent paraphyses and in pycnidial production, but it differs from M. disseminatum in having excipular and pycnidial walls reddish brown, in having smaller spores which are 1-septate at maturity, and in having narrowly ellipsoid conidia. It also differs in that the pycnidial wall is K+ aeruginose, N+ dark reddish brown.