Parmelia saxatilis (L.) Ach. agg.

    Foliose thallus loosely attached to the substrate, often in a rosette of elongated lobes with truncated and sometimes brown ends, 10-15 cm in diameter. Upper surface of the lobes smooth to sometimes foveolate, gray, bluish-gray, greenish-gray, rarely brownish-gray... traversed by a network of whitish pseudocyphellae and covered, especially in the center, with more or less cylindrical isidia, simple or sometimes coralloid, whitish with a graying apex. Underside blackish with simple or forked rhizines, black. Apothecia rare, lecanorine, 2-8 mm in diameter, brown disc, isidiate margin. Simple spores, hyaline, elliptic, (11) 13-15 (18) x 6-8 (11) µm. Pycnidia black, conidia bacilliform, 5-8 x 1 µm. Photobiont: Trebouxia. Cortex: C-, K+ yellow turning dirty yellow-orange, KC-, P-, UV+/- purple. Medulla: K+ yellow → red-orange, C-, KC-, P+ red-orange, UV+/- purple. Mainly saxicolous species found on non-calcareous rocks, but also corticolous, rarely on the ground at the foot of rocks.

Two forms can be distinguished:

_ Parmelia saxatilis forme saxicole that grows on siliceous rocks.

_ Parmelia saxatilis forme corticole form that grows on the bark of trunks or large branches of trees, very isidia and more grayish-brown.

N.B. There are two very closely related species, in fact so closely related that they can only be identified with certainty by DNA analysis:

_ Parmelia ernstiae with conical isidia or small leaflets (phyllidia).

_ Parmelia serrana a Mediterranean and Macaronesian species with mountain tendencies and thinner isidia.

N.B. This species is often parasitized by Marchandiomyces corallinus.