Roccella tinctoria DC Taxon Atlantique-Ouessant Cf.

      Thallus usually erect and tufted, 3-5 cm high and 5-8 cm across in their greatest length, more or less cylindrical branches with a terete end, with a diameter of 1-3 mm, branches arising from a holdfast more or less brownish on the outside and whitish dirty inside (rarely yellowish), smooth surface very often with initially rounded and pustular soralia, becoming globular, whitish, the coloring of the branches is pale greyish, greyish a slightly purple, brownish-gray, etc. but never reddish-brown, whitish medulla. Rather rare apothecia, marginal, 1-2 mm in diameter, rough black disc, very fine "cup-shaped" margin, concolorous to the thallus. Asci club, 80-110 x 17-22 µm according to our measurements. Spores colorless but becoming brownish in old age, elliptical "shuttle", straight or a little curved, 3-septate, 23-27 x 6-8 µm according to the literature, 25-28 x 6-8 (9) µm according to our measurements (in 5% KOH). Photobiont: Trentepohlia. Cortex and medulla K +/- yellow or K + yellow, C + instant bright carmine red. Rare thermophilic and Macaronesian saxicolous species coming on the vertical faces of the coastal rocks of the southwest of the island of Ouessant but see a very similar taxon, if not identical, which comes on the sunny faces of the large coastal rocks of the northern coast of Finistère and in the other Atlantic Islands : Roccella tinctoria Taxon Atlantique. NB Strongly resembles Roccella phycopsis with which it can be mixed but this last species does not react as strongly in carmine red to C and its medulla is yellow-orange at the base (character does it seem unreliable!), But it seems there are intermediaries and this Ouessant taxon in Finistère (under study) could be a chemotype of Roccella phycopsis because it seems different from Mediterranean (Corsica) and Macaronesian taxa subjected to different climatic conditions and much more colorful: see Roccella tinctoria taxon de Méditerranée-Corse and Roccella tinctoria taxon de Macaronésie see also Roccella phycopsis forma. The name of this fairly well characterized taxon is therefore only provisional.