Description: ThaIlus crustose, episubstratic, continuous to rimose-areolate, grey to grey-green, sometimes delimited by a dark prothallus. Apothecia lecideine, (0.5-)0.5-0.8(-1.1) mm across, with a convex, usually epruinose, dark purple-brown to black, often mottled disc, and a concolorous or slightly paler, smooth, persistent or rarely excluded proper margin. Proper exciple 45-120 µm wide, without crystals or rarely with radiating clusters of crystals, brown or red-brown in upper and outer parts, pale yeI1ow to colourless within, the pigmented parts K+ purplish; epithecium brown to black-brown, K+ purplish N+ orange-red, the pigment dissolved in the gelatinous matrix or as granules between apices of paraphyses; hymenium colourless or with brown vertical streaks, 75-115 µm high; paraphyses 0.8-1.6 µm thick at mid-level, the apical cells not swollen to clavate, (1.2-)2-3(-4) µm wide; hypothecium colourless or pale yellow. Asci 8-spored, cylindrical-clavate, surrounded by a gelatinous I+ blue coat, with a well-developed I+ blue tholus, a I+ darker blue tube and a well-developed ocular chamber, Bacidia-type. Ascospores (2-)4-12-septate, hyaline, needle-like, straight to slightly curved, (32-)36-67(-73) x (2.5-)3-4(-4.3) µm. Pycnidia partly or entirely immersed, dark in uppermost part. Conidia simple, thread-like, curved, 5-10 x c. 1 µm. Photobiont chlorococcoid. Spot tests: thallus K- or rarely K+ yellowish, C-, KC-, P-. Chemistry: thallus without lichen substances or with traces of atranorin; epithecium, rim of proper exciple, and pycnidial wall with the Laurocerasi-brown pigment; hypothecium and inner part of proper exciple with the Rubella-orange pigment.
Note: a humid subtropical to Mediterranean-Atlantic lichen found on smooth bark of broad-leaved trees in open humid forests; most frequent in Tyrrhenian Italy. According to Ekman (in litt.) the species might have been confused with B. heterochroa in the past (see note to B. heterochroa).
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)