Fissurina nigrolabiata

Fissurina nigrolabiata forms a thin, bark-dwelling (corticolous) crust up to about 5 cm across and only 30–50 micrometres (μm) thick. Its surface is smooth to slightly uneven, glossy green, and protected by a narrow brick-like (prosoplectenchymatous) cortex. Just beneath this skin lies an irregular layer of green algae along with conspicuous clusters of colourless crystals—features that give the thallus a subtly speckled look in thin section. The reproductive structures are elongated slits called lirellae. These are straight to gently curved, seldom branched, and protrude slightly from the bark, measuring 1–3 mm long and roughly 0.3–0.4 mm wide and high. Each lirella is framed by a cream-coloured thalline margin, but its lips (labia) are thick, grey-black to brown-black, and capped by a thin translucent cortex; the disc itself remains hidden. Internally the entire exciple—tissue surrounding the hymenium—is heavily blackened (carbonised), reaching 200 μm thick beneath the hymenium. The colourless hymenium rises 120–180 μm and contains eight spindle-shaped asci (80–100 × 15–20 μm) per locule. Each ascus produces eight ellipsoid ascospores divided by several cross-walls (a muriform arrangement), usually 12–17 × 5–8 μm and about twice as long as broad. No secondary metabolites were detected by thin-layer chromatography, and the species lacks detectable asexual propagules.

Fissurina nigrolabiata is a corticolous (bark-dwelling) species and has been documented from the Philippines, and from Brazil.

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