Ocellularia thailandica is a
bark-dwelling lichen with a body (
thallus) that grows on the bark surface (epiperidermal) and reaches up to about 5 cm across. The thallus is continuous, light yellowish green, and has an uneven, warty to cracked surface. The inner tissue (
medulla) is white, and no visible border zone () is present. In cross-section, the thallus is 40–60
μm thick and consists of a thin outer skin (, 5–7 μm), an algal layer (, 15–25 μm), and a medulla (20–30 μm) with scattered clusters of
calcium oxalate crystals. The algal
photosynthetic partner () is the green alga
Trentepohlia, with cells about 7–8 × 5–9 μm. The fruiting bodies (
ascomata) are rounded and partly protruding from the thallus (), with a complete covering of thallus tissue (), measuring 0.3–0.5 mm across and 0.12–0.2 mm high. The is hidden beneath a small pore-like opening 0.05–0.1 mm wide, ringed by a whitish rim. A finger-like, blackened () central column () is present, up to 100 μm broad and 120–135 μm high. The spore-bearing layer (
hymenium) is clear and 125–140 μm high. The
asci are cylindrical to narrowly club-shaped (), 87–100 × 12–15 μm, each containing eight colourless (
hyaline), oval (
ellipsoid)
ascospores. The spores are divided into 6–8 cells (5–7-
septate) and measure 20–23 × 7–8 μm, with thick cross-walls and lens-shaped internal spaces ( with lens-shaped ). They
stain violet-blue with iodine (I+ violet-blue).
Pycnidia (
asexual fruiting bodies) were not observed, and no
lichen substances were detected by
thin-layer chromatography. ==Habitat and distribution==