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DescriptionLife habit: lichenized or not, lichenicolous when young, persistently lichenicolous or not lichenicolous; Thallus: crustose or forming a mycelium in host species in some lichenicolous species, when present usually areolate, more rarely partly endolithic, continuous, cracked, verrucose, or slightly effigurate at the margin, rarely sorediate or isidiate; prothallus: usually present; cephalodia: present in one species; upper cortex: usually a well developed pseudo-cortex, often containing lichen substances, calcium oxalate or melanins; medulla: white or rarely yellow, KI- to KI+ dark violet, often containing lichen substances; photobiont: primary one a green, unicellular algae, secondary one absent; lower cortex: usually absent but present in a few species with peltate areolae, composed on dense cells, KI+ blue in one species; Ascomata: apothecial, attached to the hypothallus, black, slightly concave to strongly convex, marginate when young, later persistently marginate or becoming immarginate; thalline exciple: absent; proper exciple: usually well developed, composed of radiating hyphae, with a brownish or greenish black rim and a usually somewhat paler or rarely hyaline inner part, frequently containing crystals of lichen substances; epihymenium: dark brown or green, frequently containing crystals of lichen substances; hymenium: hyaline or slightly brown or green, KI+ blue; paraphyses: conglutinated, richly branched and anastomosing, with a slightly to distinctly thickened apical cell; hypothecium: medium brown to dark brown, lacking crystals; asci: clavate, with a well developed tholus which is non-amyloid in the lower part and amyloid near the apex, lacking an ocular chamber, 1-8spored; ascospores: hyaline to dark green or dark brown to black, 1-septate to muriform, +ellipsoid, halonate; Conidiomata: pycnidial, known in a few species only, attached to the hypothallus or immersed in the areolae; conidia: hyaline, bacilliform to acicular; Secondary metabolites: depsides, depsidones, pulvinic acids, or rarely aliphatic acids or no secondary metabolites; Geography: cosmopolitan, but predominately temperate/boreal to arctic/alpine; Substrate: on rock, mainly non-calcareous, or lichenicolous on saxicolous lichens, rarely on wood.; Notes: The amyloid reaction of the medulla is best studied in an acidic ioidine solution (e.g., Lugol's solution with the water substituted by 25% lactic acid) after a few seconds pretreatment in K; this is here denoted the KI-reaction. Rhizocarpon athalloides (Nyl.) Hasse is reported on soil from southern California, but the species does not appear to be a Rhizocarpon; it's proper placement is uncertain at this time.