Thallus: crustose, discontinuous, composed of discrete or partly contiguous, usually convex areoles, or continuous surface: ±gray, gray-green, green-brown, or gray-brown, smooth to warted, with or without cracks Apothecia: at first flat, usually remaining so or sometimes becoming ±convex, 0.2-0.8 mm in diam.; without pruina disc: usually black, only rarely ±pigment deficient margin: usually concolorous with disc, often markedly glossy, at first distinct, slightly raised above or ±level with disc, persistent or rarely finally excluded exciple: laterally 20-70 µm wide, without crystals, gray-green, blue-green, or ±brown to black in upper part and along rim, interior often ±fading to colorless or pale brown or brown-orange below (dominant brown pigment K+ purplish, N+ orange, accessory greenish pigment K-, N+ purple); edge: with single cell layer of enlarged cell lumina (up to 7 µm wide) epithecium: blue-green to olive-green, sometimes partly purplish brown, containing a blue-green (K-, N+ purple with or without blue crystals) and a purplish brown (K+ purple, N+ orange) pigment in various amounts, the former usually dominant; crystals not present hymenium: hyaline, 45-80 µm tall paraphyses: 0.8-1.6 µm wide in mid-hymenium, apices often ±clavate, 1.2-6.5 µm wide, without distinct hoods of pigment hypothecium: entirely colorless or upper part sometimes pale straw to brown-orange (K+ intensifying) asci: clavate, 8-spored ascospores: hyaline, usually 3septate but occasionally with up to 9 septa, bacilliform to clavate, straight to curved, 11-45 x 1.6-3.3 µm Pycnidia: half-immersed or almost sessile, bluish or black, 75-100 µm in diam. conidia: composed of three types (not mixed in a single thallus): (1) oblong to fusiform to bacilliform, 01-septate, 7-12 x 1.2-1.9 µm, (2) filiform, curved, simple, 8-19 x 0.5-08(-1) µm, and (3) falcate, 0-1-septate, 6-25 x 1.2-1.6 µm Spot tests: all negative Secondary metabolites: none detected. Habitat and ecology: on bark of various broad-leaved trees in open woodlands from sea-level to 3000 m World distribution: North America and Europe Sonoran distribution: known from scattered localities along the coast of California and Baja California and from a few inland locations in the mountains of north-central and northeastern Arizona and the west side of the Sierra Madre Occidental. Notes: Bacidia circumspecta in the sense of Ekman (1996a) could constitute an aggregate of similar species. There seems to be some correlations between morphology on the one hand and geography on the other. An initial step towards an improved classification is taken here in the recognition of B. veneta as a species distinct from B. circumspecta. Reports by Ekman (1996a) of B. circumspecta specimens with brown and K+ purple hypothecium correspond to B. veneta.