Roccella tinctoria DC Taxon Atlantique-Ouessant Cf.
Thallus usually erect and tufted, to 3-5 cm high and 5-8 cm across, branches more or less terete, 1-3 mm diam., arising from a holdfast, outer brownish and inner side dull whitish, apices pointed, surface smooth often with soralia, soralia rounded and pustulose at first, becoming globose, whitish, branches pale grey, greyish tinged with purple, grey-brownish, etc., never brown-reddish, medulla white. Apothecia scarce, marginal, 1-2 mm diam., black. Ascospores 3-septate, 23-27 x 6-8 µm. Photobiont: Trentepohlia. Cortex and medulla K+/- yellow, C+ instantly carmine. Rare, saxicolous, thermophile and Macaronesian, on vertical walls of foreshore rocks in the S-W of Ouessant island. N.B. Not to be confused with Roccella phycopsis that grows together but the C+ carmine reaction is not immediate for the latter, its medulla is yellow-orange towards the base (but this is not a hallmark). Intermediate taxa between the two species seem to grow in the Finistère (still under investigation) and we cannot exclude that it is a chemotype of Roccella phycopsis since it clearly appears different from Mediterranean taxa from Corsica subjected to different climatic conditions and above all mahogany. See Roccella tinctoria Méditerranée-Corse. As a consequence, the present description is merely provisional, see Roccella phycopsis forma.
Tehler A., Dahlkild A., Eldenäs P. & Feige G.B. 2004. The phylogeny and taxonomy of Macaronesian, European and Mediterranean Roccella (Roccellacea, Arthoniales). Acta Univ. Ups. Symb. Bot. Ups. 34:1, 405-428.