Halegrapha paulseniana

Halegrapha paulseniana is a bark-dwelling, crustose lichen that forms a continuous, uneven, cream-white thallus up to about 5 cm (2 in) across. In section, the thallus has a thick upper layer over an irregular algal zone and a distinct medulla, and parts of the thallus are encrusted with grayish crystals; the thallus tissue over the fruiting bodies can contain clusters of calcium oxalate crystals. The photobiont (photosynthetic algal partner) is Trentepohlia.^[2]

The fruiting bodies are lirellae (elongated, script-like structures) that are flexuose and irregularly branched, typically 3–8 mm long. They break through the thallus surface and have a thalline margin that is thick on the sides but thin at the top. The disc is partly exposed and dark brown to nearly black, with entire labia (raised edges). The excipulum (the wall surrounding the disc) is largely carbonized, but the lateral portions are often only weakly carbonized or uncarbonized. The asci contain eight spores; the ascospores are oblong to oval, usually 5–7-septate, about 20–25 × 7–8 μm, and turn brown at maturity (becoming darker and shriveled when overmature). No lichen substances were detected by thin-layer chromatography.^[2]

Halegrapha paulseniana is known only from the Waikamoi Preserve on Maui, Hawaii, where it was collected at about 1,200–1,300 m (3,900–4,300 ft) elevation in disturbed primary forest on Haleakalā volcano. The site was described as forest dominated by Acacia koa and members of the Campanulaceae, with the invasive ginger Hedychium gardnerianum present in lower parts of the area. Because it has not yet been found elsewhere, it has been treated as a putative Hawaiian endemic. The authors noted that parts of the preserve are threatened by the spread of Hedychium gardnerianum, which can overtake forest ecosystems and may endanger local endemic species.^[2]