Trentepohlia umbrina (Kuntz.) Bornet s.l.
Filamentous terrestrial green algae whose red coloration is due to carotenoid pigments which mask the green coloration of chlorophylls. This alga is often symbiotic of lichenized fungi of which it constitutes the photobiont, in particular Belonia nidarosiensis, but it can have an independent existence which we describe here. The free form appears as streaks or large plates, the surface is grainy but can become lumpy by the formation of small coarsely velvety pads or beads 0.2-1 mm in height, formed of entangled filaments, these filaments are made up of short cells arranged in small strings with a few sporocysts, these cells become independent in old age. The color is red-orange at the beginning, then wine-red and finally dark brown, the surface can become whitish by degradation of the ends of the filaments and take a soredioid appearance. Species preferring alkaline substrates, humid and in the shade, frequent on walls, cement in particular on the walls of old chapels. NB The specimens appearing on the walls of the chapels were in the past inventoried as luxuriant specimens of Belonia nidarosiensis whose photobiont resumed its free life, currently we prefer to consider these specimens as Trentepohlia umbrina sl (with a sl pending a clarification of the group of this species which contains several taxa).