Coniarthonia gregarina

The lichen body (thallus) is a thin, whitish, crust-like growth that spreads across the bark and can disrupt the bark surface; in cross-section it is about 30–50 μm thick. The surface shows fine cracks and is bordered by brownish boundary lines (prothallus). The algal partner (photobiont) is indistinct but is thought to be the green alga Trentepohlia; its cells are about 10–14 × 7 μm. The fruiting bodies (ascomata) are scattered and broadly protruding from the bark (erumpent), usually roundish to spot-like, about 0.25–1.25 mm across and 75–120 μm thick in cross-section. They sit level with the thallus and are often partly covered by bark fragments. The surface of the fruiting bodies is crimson-red and frosted with pigment (pruinose), with areas above mature spore-bearing structures (asci) turning brownish. The red pigment occurs as fine crystalline grains that can clump together into larger aggregates. Under the microscope, the uppermost tissue layer (epithecium) is densely pigmented and water-repellent (hydrophobic, about 25–40 μm thick), and the asci are more or less dispersed, spherical to nearly spherical (globose to subglobose, about 77–90 × 45–60 μm) with a distinct stalk. …

Coniarthonia gregarina is a bark-dwelling, lichen-forming species recorded from smooth bark. It was originally known from Florida based on the type and additional examined material. The lichen was later recorded from Mato Grosso do Sul, Brazil. Grube noted that it can resemble C. pyrrhula and C. wilmsiana at a glance, but it differs from both by its muriform ascospores and by having a smaller amount of reddish pigment in the ascomata; young spores with only three septa may resemble the mature spores of C. wilmsiana. Because the available material was limited, secondary chemistry was not analyzed by thin-layer chromatography.

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