The
thallus of
Buellia oidalea is
crustose, varying from thin and
rimose-
areolate to thick and rugose-
verrucose or even
subsquamulose. The
prothallus is often present, appearing black. The thallus surface is yellowish white to glaucous gray, smooth, and esorediate. The
medulla is white and lacks
calcium oxalate. The
apothecia of
B. oidalea are
lecideine and commonly found, ranging from 0.2 to 2 mm in diameter, and are sessile in nature. Initially, the disc is black, devoid of
pruina, and flat, but as it matures, it becomes convex. The margin starts as distinct but eventually becomes excluded and black. The proper exciple measures between 35 and 95 μm in thickness, lacking secondary
metabolites, and appears uniformly dark brown throughout, with
carbonized cells smaller than 6 μm. It is transient and accompanied by a brown hypothecium, which is less than 280
μm thick. The
epihymenium shares a continuous brown pigmentation with the outer exciple. The hymenium is hyaline, generously interspersed with oil droplets, and measures 115 to 165 μm in height. The tips of the
paraphyses typically measure less than 3 μm in width and are adorned with distinct apical caps. Asci are clavate, of
Bacidia-type, measuring 95 to 112 x 20 to 40 μm, and typically contain 8 spores. The ascospores of
B. oidalea typically exhibit a
hyaline to ±olive coloration, eventually transitioning to brown, while often retaining unpigmented apices. They possess a muriform structure, comprising 13–40 cells in optical section, and are ellipsoid to oblong in shape, measuring (29.5-)33.7-[39.6]-45.5(-57) x (12.5-)13.3-[15.5]-17.7(-26.5)
μm. The
ascospores feature apical, lateral, and septal wall thickenings, with the apical thickenings often being permanent. Their proper wall is approximately 1.2 μm thick, and they lack a perispore, with no discernible ornamentation visible under DIC.
Pycnidia are rare, immersed with only the uppermost part protruding, and the wall is mainly pigmented in the upper part. The conidia are bacilliform, 4-6 x 1 μm. == Chemistry ==