Coniarthonia aurata

Coniarthonia aurata is a species of crustose lichen-forming fungus in the family Arthoniaceae.^[1] It is characterized by its mustard-yellow, hemispherical fruiting structures that give the thallus a granular appearance. The species is known from northeastern Brazil, where it grows on tree bark in Caatinga vegetation.

Coniarthonia aurata was described as a new species in 2013 from northeastern Brazil, based on material collected in Vale do Catimbau National Park (Pernambuco) on tree bark at about 900 m (3,000 ft) elevation. The holotype (E. L. Lima 684) is housed in ISE.^[2]

The authors placed the species (somewhat schematically) in Coniarthonia because it matches the genus in its weakly differentiated, hydrophobic-looking ascigerous (ascus-producing) structures, club-shaped asci, and single-septum ascospores, as well as the presence of pigmented crystals in the ascoma. It differs from previously known species in the genus by having mustard-yellow (rather than red) crystals, and it is further distinguished by its unusual "soralium-like" fruiting structures that contain loosely arranged asci. In overall appearance it can resemble a sterile Tylophoron (whitish thallus with spot-like patches), but C. aurata is fertile and the patches are mustard yellow rather than nearly black.^[2]

The thallus of Coniarthonia aurata is crustose, very thin, nearly white, and closely appressed to the bark; it lacks a cortex and a visible prothallus. The photobiont is a trentepohlioid green alga.^[2]

The ascigerous structures are sessile, hemispherical, mustard yellow, and about 0.2–0.4 mm in diameter, giving the thallus a sorediate or "soralium-like" look at first glance. The asci are clavate (about 60–70 × 23–28 μm) with the upper part of the wall thickened, and the hamathecium consists of curled, anastomosing hyphae encrusted with golden crystals. Each ascus contains eight hyaline ascospores that have a single septum (1-septate) and are club-shaped (clavate) (about 20–28 × 7–11 μm), with the upper cell much larger than the lower, and without a perispore. Pycnidia were not observed.^[2]

In spot tests, the ascigerous structures were UV−, C−, and P−, with a K+ (purple) reaction. Thin-layer chromatography detected an anthraquinone.^[2]

The species is corticolous, occurring on smooth bark of trees in Caatinga vegetation. The type collection was made on moderately rain-exposed (not sheltered) bark.^[2]

In the type locality it was reported growing with several other crustose lichens, including Acanthothecis abaphoides, Chrysothrix xanthina, Dirinaria leopoldii, Glyphis scyphulifera, Graphis furcata, Lecanora leprosa, Phaeographis ventosa, and Ramboldia haematites.^[2] Originally described from collections made in Pernambuco, C. aurata was later recorded from Mato Grosso do Sul.^[3][4]