Lithothelium bermudense

The lichen grows within the surface of calcareous rock (endolithic), presenting externally as a faint pink to pale brown spot up to about 2 cm across; no prothallus is visible. Its photosynthetic partner is a Trentepohlia alga with cells around 8 micrometers (μm) in diameter. The fruiting bodies (perithecia) are single, conical, and black; at about 0.4–0.6 mm across they sit mostly submerged in the rock and leave tiny dark pits. they leave small black pits and have a brittle, carbonised wall in which the exciple and involucrellum are integrated. The ostiole is small and centrally placed. Under the microscope the paraphyses are simple and slender. The asci are about 110 × 25–30 μm, cylindrical to club shaped, with a rounded ocular chamber, and typically hold 6 to 8 spores. The ascospores are fusiform, reddish-brown (darkening in KOH) and typically 20–25 × 7–8 μm. They show three internal partitions in the spore wall (distosepta) that give the inner lumina a distinctive diamond shape; during maturation a true median septum develops, and in over-mature spores two additional eusepta can appear. The terminal lumina are smaller and protrude toward the spore ends; no perispore or wall ornamentation was observed, and pycnidia were not seen.^[2]

The species was found on low, sheltered limestone outcrops within primary coastal forest at Walsingham Nature Reserve, an area that retains Bermuda's native woodland. It occurs with other calcicolous crustose lichen and liverworts; associates reported from the type site include Ionaspis tropica, Stromatella bermudana, Strigula bermudana, Gyalecta farlowii, Cryptothecia striata, and several small gelatinous and cyanolichens. As of its original publication, L. bermudense was known to occur only from the type collection and is endemic to Bermuda; the authors suggest that given that tropical limestone outcrops are patchy and the species is inconspicuous and easily overlooked, its apparent rarity may reflect both a genuinely narrow range and under-collection.^[2]