Lichens marins - Immersaria athroocarpa (Ach.) Rambold & Pietschm.

Thallus crustose rather thick, cracked and areolate, formed of irregular and angular areoles, well separated, sometimes by a paler and whitish margin, and revealing a blackish hypothallus, flat to concave, yellow-brown, brownish, greyish-brown, reddish-brown. Apothecia usually numerous, angular, 0.5-2 mm in diameter, typically sunken in the thallus, flat concave disc, blackish but may appear greyish with a gray bloom, fine margin disappearing at the end but the apothecia are sometimes surrounded by 'a clear and whitish area more or less in relief. Colorless, broadly elliptical spores with a thin perispore, 12-26 x 6-12 µm. Photobiont: chlorococcoid. C-, K-, KC-, P-; I + blue. Colline and mountainous species, rare in our prospecting area, coming on the horizontal siliceous rocks of the rocky ridges of central Brittany. Parasite, at least at the beginning of other crustacean lichens, in particular of the genus Aspicilia. N.B. In the field, strongly resembles Lecidea fuscoatra but this last species has more or less sessile apothecia and is C + red.