The
thallus of
Buellia kowenensis is crustose, , and can grow up to 10 mm wide and 0.3 mm thick. The , or cracked segments, range from 0.1 to 0.7 mm wide. The upper surface is white to off-white, dull, and appears crystalline or spotted due to the incorporation of
silica. It does not form and lacks a distinct bordering . The cells are 8–14
μm wide. The
medulla is white, contains
calcium oxalate (as indicated by a positive
sulphuric acid reaction), and does not change colour when
stained with
iodine. The , or fruiting bodies, are 0.1–0.4 mm wide, in type, and can be separate, broadly attached, with a black, non-powdery, and either weakly concave or convex disc. The , the rim around the disc, is thin, initially raised above the disc, but becomes thinner and level with the disc in older apothecia. The outer part of the exciple is dark brown, measuring 15–25 μm thick, and the beneath the spore-producing tissue is deep red-brown, 50–60 μm thick. The is dark brown and 10–12 μm thick. The
hymenium is 50–60 μm thick, colourless, and the beneath it is pale brown, 10–15 μm thick. The
paraphyses are 1.5–2 μm wide, sparsely branched, with brown-capped tips. The
asci are of the
Bacidia type and contain eight spores. The ascospores are of the
Buellia type, 1-septate, brown,
ellipsoid, measuring 9–13 by 5–7 μm, and older spores are constricted at the septum; the outer spore-wall is microrugulate. are punctiform, immersed, with a brown . The are , measuring 8–10 by 1 μm. The medulla contains
isoarthothelin as a major component and 4,5-dichloronorlichexanthone in trace amounts.
Buellia kowenensis resembles
Buellia halonia but is distinct due to its smaller, persistently
Buellia-type and the presence of medullary calcium oxalate. ==Habitat and distribution==