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DescriptionLife habit: lichenized; Thallus: usually immersed in substrate, rarely episubstratic, dark grayish green, verrucose, very thin; Apothecia: black, with a yellow pruina on lower side of capitulum, and sometimes a little on the mazedium, 0.5-1 mm high,; stalk: 5-9 times as high as the width of the stalk, 0.07-0.11 mm in diam., the central part dark brown or with an aeruginose tinge, composed of intricately interwoven and heavily sclerotized hyphae; outer part: hyaline to brown, 22-27 µm thick, composed of strongly gelatinized cells arranged as in the central part, with a thin gelatinous coat; capitulum: top-shaped or obovoid to lenticular, 0.17-0.26(-0.5) mm wide, with hyaline mantle; exciple: dark brown or green, composed of isodiametric to slightly elongated, sclerotized cells; outer part: pale, with surficial granular, yellow pruina; hypothecium: blackish brown, with a convex upper surface; asci: cylindrical, 30-37 x 3.5-4.5 µm; ascospores: semi-mature spores: with irregular sulcate pattern; mature spores: ellipsoid, 712(-14) x 4-6 µm, with a very irregularly cracked surface; Spot tests: thallus K-, C-, KC-, P-, all parts of apothecia I-; Secondary metabolites: pruina of the apothecia contains vulpinic acid.; Substrate and ecology: on wood, including old fence posts and decorticated conifer deciduous tree stumps, in open to moderately shaded, not too dry situations; World distribution: Africa, Europe, Asia, North and South America, and Australasia; Sonoran distribution: Arizona at c. 2000 m in mixed conifer-oak forests.; Notes: Calicium trabinellum is characterized by its immersed thallus, rather short ascomata, yellow pruina on the lower side of its capitulum, and its spore ornamentation. It is very similar to C. glaucellum, which, however, has a whitish pruina.