Wahlenbergiella mucosa (Wahl.) Gueidan & Thüs

    Thallus crustose, thin, 0.2-1 mm thick, up to 10 cm diam. or more, slightly gelatinous, typically bronze green, greenish, olive green, fatty and shiny aspect when moist, smooth or seldom cracked in very limited patches, white prothallus distintively delimiting (rather often absent). Perithecia dark green olive, immersed or very slightly prominent, 0.1-0.2 mm diam., (only ostioles are visible, as minute black dots). Ascospores simple, broadly ellipsoid, thick walls, 7-10 x 4-7 µm. Rather rare, on rocks and boulders, rather low on the foreshore, always immersed at high tides (in limpets zone (Patella sp.) that may graze on, barnacles  (Balanus) and Hildenbrandia rubra red algae zones, mainly on rocks beated by the waves. N.B. Not to be confused with two other green species thriving in this zone: Verrucaria (Wahlenbergiella) striatula and Verrucaria halizoa but these species have prominent and easily visible perithecia. Much higher on the foreshore, in the Hydropunctaria maura zone, two other confusing green (sometimes) species may also be found, but their thalli are cracked: Hydropunctaria orae and Hydropunctaria oceanica.*