Pyrenula aurantiothallina

Pyrenula aurantiothallina is a crustose (crust-forming), bark-dwelling lichen in the family Pyrenulaceae.^[1] It was described as new in 2016 from specimens collected in northeastern Brazil.^[2]

It forms a rather thick body (thallus) with a uniformly orange, smooth, dull surface, lacking both pseudocyphellae (tiny pores in the surface) and a visible border zone (prothallus). The algal partner (photobiont) is a trentepohlioid green alga. Its fruiting bodies (perithecia) are partly sunken in the thallus (erumpent), low-conical, and usually 0.7–1.0 mm across, with brown pore-like openings (ostioles) at the apex. The sterile tissue inside the fruiting body (hamathecium) is filled with colorless (hyaline) oil droplets. The asci contain eight ascospores arranged in a single row, which are brown and divided into 4 cells by 3 septa. The spores measure about 19.5–22.5 × 7–8.5 μm, are often slightly pinched at the cross-walls, and have diamond-shaped internal spaces (lumina). Pycnidia (asexual fruiting bodies) were not observed. The thallus gives a purple reaction with potassium hydroxide solution (the K spot test), indicating an anthraquinone pigment; it is UV−, and thin-layer chromatography detected an unidentified anthraquinone.^[2]

The species is known from primary forest in Bahia, including the Chapada Diamantina area (type locality near Povoado Ouro Verde–Catolé at about 1,636 m (5,367 ft) elevation), where it grows on smooth bark of trees and branches. Additional collections were reported from the same general locality.^[2] It had not been reported from any other Brazilian states as of 2025.^[3] The original description compared it with Pyrenula mamillana based on fruiting body and spore characters, separating P. aurantiothallina by its uniformly orange thallus. Other orange-thallus Pyrenula species were noted to differ in ascospore characters.^[2]

• List of Pyrenula species