Polymeridium longiflavens

Polymeridium longiflavens is a species of corticolous (bark-dwelling) crustose lichen in the family Trypetheliaceae, first described in 2016. It is found in Brazil.

Taxonomy
Polymeridium longiflavens was formally described by André Aptroot, Cléverton de Oliveira Mendonça, and Marcela Eugenia da Silva Cáceres in 2016. The type specimen was collected in the Serra de Itabaiana National Park, Sergipe, Brazil, at an elevation of approximately 400 m.

Description
The thallus of Polymeridium longiflavens is not, dull, continuous, covering areas up to 2 cm in diameter, and whitish-grey in colour. It is surrounded by a cottony dark brown line approximately 0.4 mm wide and does not induce gall formation on the host bark. Ascomata are spherical, measuring 0.25–0.35 mm in diameter, single, and emergent from the thallus. The wall is and up to 40 μm thick. Ostioles are apical, not fused, flat, and black. The is inspersed with yellow oil globules. Asci contain eight each. Ascospores are hyaline, have between 9 and 11 septa,, measuring 57–70 by 12–14 μm, with pointed ends and rounded , and are not surrounded by a gelatinous layer. were not observed.

The thallus surface of Polymeridium longiflavens is UV+ (yellow), but does not react with standard chemical spot tests. Thin-layer chromatography analysis reveals the presence of lichexanthone.

Habitat and distribution
This species is found on the smooth bark of trees in transitional forests and at the time of its original publication was known to occur only in Brazil.