Astrothelium nicaraguense

The thallus is crustose and grows on bark, forming a continuous patch up to about 3 cm (1.2 in) in diameter. It is olive-green and uneven to somewhat blistered in texture. In cross section, it has a thick, cartilage-like cortex, a distinct photobiont layer positioned near the surface, and a thick medulla.^[2]

The perithecia (flask-shaped fruiting bodies) are either solitary or loosely aggregated into diffuse pseudostromata. They are erumpent to prominent, up to about 1 mm tall and 0.9–1.2 mm across, and are usually covered by an olive-green layer of thallus tissue except at the ostiolar area. The ostioles are apical to slightly irregularly oriented and appear as black dots about 0.05–0.10 mm wide within a dark gray-brown area bordered by a whitish rim. Individual perithecia are pear-shaped, about 0.6–0.8 mm wide and 0.8–1.0 mm high. The excipulum is carbonized and about 70–100 μm thick. The hamathecium consists of a clear gelatinous matrix with a dense, net-like system of very thin, branching paraphyses; it is iodine staining-negative (IKI−), and the ostiolar channel is also clear.^[2]

Each ascus contains a single ascospore. The ascospores are hyaline, oblong-ellipsoid, densely muriform (divided into many small compartments by internal walls), and lack a median constriction, measuring about 160–200 × 40–60 μm; they are iodine-negative (IKI−). No secondary metabolites were detected.^[2]

The species is known from montane rainforest in the Reserva Natural Volcán Mombacho near Granada, Nicaragua. Collections were made in slightly disturbed forest along a trail leading toward the crater, where the lichen was found on woody substrates, including a fallen trunk and other tree trunks. In addition to the type collection at about 1,000 m (3,300 ft) elevation, further specimens have been reported from the same reserve at around 800 m (2,600 ft).^[2] It has also been recorded from Amazonas state in Brazil,^[3] and from Costa Rica.^[4]