Micarea pauli

Micarea pauli has an indeterminate crustose thallus that grows within or on its bark substrate, appearing as a greenish film. The thallus, which lacks a prothallus, comprises tiny areoles about 0.1 mm in diameter that develop branched and coral-like (coralloid) isidia that are densely packed to form a nearly continuous layer over the thallus. Apothecia occur rarely; when present, they are beige with spots of grey pigment measuring up to 0.5 mm in diameter. Asci contains eight spores and measure 30–35 by 9–12 μm. The ascospores range in shape from ovoid, to ellipsoidal, to oblong, and have dimensions of 7–13 by 3.5–4.5 μm; some of them have a single septum. Micarea pauli contains methoxymicareic acid, a lichen product that can be detected using thin-layer chromatography.^[1]

Micarea aeruginoprasina and M. nigra are somewhat similar in morphology, but can be distinguished from M. pauli by differences in apothecial pigmentation.^[1]

Micarea pauli is only known to occur from a few locations in the Białowieża Forest. Most specimens have been recorded on the bark of Alnus glutinosa, but it has also been found on the bark of Tilia cordata and on decorticated wood.^[1]