Thallus filamentous, tufted, in small pulvinate rosettes, or irregularly straggling, by small holdfasts. Branches of filaments paired, apices discrete, hyphae in a rectangular arrangement of forming an irregular network, both types arising from a basal strand. Basal strand of hyphae distinct in younger parts of thallus, persistent in some species. Photobiont blue-green, . Apothecia lateral, disc brown or dark green, with a thalline margin, concolorous with thallus. Paraphyses either richly branched and anastomosing paraphysoids (primary paraphyses) or distinctly septate, true paraphyses (secondary paraphyses). Asci prototunicate, cylindrical, clavate or obclavate, 8-24 or more-spored. Ascospores simple, often with a plasma bridge, colourless. Pycnidia lateral, the ostiole brown or dark green. Conidia small, rod-shaped, developing from the tips of unbranched elongated conidiophores.