Parmelia serrana

Parmelia serrana features a crustose, epilithic thallus that is closely adpressed to the substrate and forms orbicular patches up to 15 cm in diameter. The thallus consists of overlapping (imbricate) lobes, which are typically 2.5–6 mm wide, apically rounded to sublinear, and show a pale greenish grey to whitish grey colour. The surface is shiny and may become reticulately cracked as it ages. Pseudocyphellae (tiny pores for gas exchange) are numerous and mainly linear to irregularly shaped, scattered across the lamina. Over time, the pseudocyphellae become sorediate, forming orbicular to linear soralia with eroded centres as they age. Isidia are densely packed on older parts of the thallus, cylindrical in shape, and simple to branched. The lower surface has sparse to moderately abundant, simple to sparsely branched rhizines, which measure 1–1.5 mm long. Apothecia (fruiting bodies) are fairly common, subpedicellate, with a disc that is initially concave, expanding to 1–4 mm in diameter. Ascospores are broadly ellipsoid, measuring 17–18 by 12–13 μm. Chemical spot tests on the thallus reveal a cortex that reacts K+ (yellow); the medulla shows a K+ (yellow then red) reaction, C−, PD+ (red-orange). Known chemical constituents include atranorin, chloroatranorin, salazinic acid, consalazinic acid, and trace amounts of protocetraric acid.

Parmelia serrana grows on deciduous and coniferous trees, and less frequently on mossy rocks. It is particularly prevalent on Pinus sylvestris and various species of Quercus (oak). The species is widespread in the Sierra del Guadarrama and other mountain ranges within its native Mediterranean and submediterranean zones, from approximately 300 to 1700 metres in elevation. In terms of its geographic spread, Parmelia serrana is found in Africa (notably the Canary Islands) and across Europe. While it is prevalent in Mediterranean mountains, its full distribution in Europe remains partially understood, with occurrences noted at lower altitudes in more temperate, somewhat continental regions like Austria. The species is well-adapted to the Iberian Peninsula and the Canary Islands and is successful in colonising a range of habitats within these regions.

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