Punctelia graminicola

The thallus of Punctelia graminicola measures 3.0–14.5 cm (1.2–5.7 in) in diameter. It comprises irregularly branched lobes, often crowded or overlapping, measuring 2–4 mm (0.08–0.16 in) wide. The upper thallus surface is blue-grey to greenish-grey, often with brown margins, and usually smooth and without pruina. Herbarium specimens tend to turn brown. Pseudocyphellae on the thallus surface range in number from occasional to abundant. They are circular to irregularly shaped, measuring 0.03–0.6 by 0.03–0.4 mm. The medulla is white. Propagules such as isidia or soralia are absent in this species, but sometimes the lichen forms lobules – small lobes (lacinulae) on the lobe margins that project out from the surface. Adriano Spielmann and Marcelo Marcelli have noted that Punctelia graminicola has a broad species concept, as it include individuals both with and without lacinulae. The thallus undersurface ranges in color from pale tan to light to medium brown, with sparse, light-colored rhizines. These rhizines are completely covered by a cortex. The upper cortex is paraplenctenchymatous; this means that it is made of a type of tissue in which the hyphae are oriented in all directions, analogous to the parenchyma of plants. Depending on the dimensions of the thallus, the upper cortex is between 3 and 7 cells thick. …

Punctelia graminicola grows on rocks, or on mosses that are on rocks. It has been recorded growing on a wide variety of rocks: basalt, conglomerate, granite, limestone, rhyolite, sandstone, schist, and volcanic. Much less frequently, it grows on bark. Recorded bark substrates include Fouquieria, Cupressus, and Quercus. In the United States, Punctelia graminicola occurs in the central US east to the Appalachians. It is common in the Great Plains region, extending to the southwestern part of the country. The Culbersons note that in the US, the lichen is only commonly found on trees in the centre of its range, while being largely confined to rock in the peripheries of its range. They suggest that the lichen "is primarily adapted to life on rock, extending substrate tolerance to bark only under the most favorable ecological conditions". In Mexico Punctelia graminicola is widely distributed across the northern and central parts of the country. Its range continues south into Central America. In South America, its distribution includes Argentina and Brazil. In East Africa (where it was recorded as P. semansiana), it is rare; it is known from Ethiopia, Kenya, and Tanzania.