Dermatocarpon luridum (With.) Laudon

   Thallus foliose, repeatedly lobed, mat-forming, 10-20 cm max. length, numerous lobes pleated, curled up, 5-20 mm, often convex, especially in the centre of the mat; upper surface dotted with the ostioles of perithecia, bright green when wet, grey to pale brown, white-ochreish when dry, lower surface pale brown, red-brown, with scattered holdfasts. Perithecia in low number, immersed, globose, 0,2-0,5 mm high, pale brown to slightly hyaline brown. Pycnidia numerous. Photobiont : chlorococcoide. Ascospores colourless, simple, ellipsoid, 10-20 x 6-8,5 µm. Chemical spot tests negative. but medulla I+ red. Rather frequnt on intermittently inundated, siliceous or limestone rocks and by streams and rivers, in the lower part of the inundated zone, often with Ephebe lanata. This species displays different aspects according to local conditions: bright green-yellow when wet or immersed, to inconspicuous grey-brown when dry especially when coated with dry silt. See Dermatocarpon leptophyllodes, whose lobes are smaller and the medulla I- and which is much rarer.