Life habit: lichenized; Thallus: foliose, umbilicate to peltate, monophyllous or polyphyllous, often rigid, usually less than 6-7 cm in diam., attached to substrate by a central holdfast; upper surface: white, gray or brown, smooth or ridged, sometimes pruinose, occasionally with soredia or isidia; upper cortex: usually palisade- or scleroplechtenchymatous; medulla: white, loose to compact; photobiont: primary one a single-celled green algae (Trebouxia sp.?), secondary one absent; lower cortex: scleroplechtenchymatous; lower surface: white, pink, brown, gray or black, smooth or papillate, sometimes with abundant or sparse +branched rhizinomorphs; Apothecia: present or absent, black, sessile, adnate or stipitate, leiodisc, omphalodisc, gyrodisc or actinodisc; asci: subclavate or clavate, thick-walled, apical dome I+ blue, usually 8spored; ascospores: hyaline and simple or more usually becoming brown and muriform; Conidiomata: pycnidial, flask-shaped, uni- or multiloculate, with branched, septate conidiophores; conidia: hyaline, single ovoid or bacilliform, 2-6 µm long; thalloconidia: dark brown, simple or multicellular, ovoid or irregular in shape, released from lower cortex or rhizinomorphs; Secondary metabolites: upper cortex with atranorin or brown pigments, medulla with some combination of orcinol or ß-orcinol depsides or tridepsides, ß-orcinol depsidones or aliphatic acids; Geography: occurs in alpine, boreal or sub-boreal areas all over the world, particularly in areas with "acidic" rocks.; Substrate: metamorphic, plutonic, volcanic or sedimentary siliceous rocks, e.g. granite, gneiss, sandstone (the Chinese species U. yunnana grows on bark).; Notes: In the genus Umbilicaria about one third of the species have developed a special type of asexual propagule, the thalloconidium, that is released directly from the lower cortex or rhizinomorphs (Hestmark 1990 & 1992). In the species where the option of forming thalloconidia has evolved, sexual reproduction by ascospores tends to be greatly reduced or even eliminated (Hestmark 1991). Because the genus Umbilicaria is primarily an arctic alpine genus, the occurrence in the Sonoran area is for most of the species restricted to the highest peaks and mountain ranges where alpine or boreal climatic conditions prevail. A few species, e.g. notably U. phaea, seem better adapted to the dry desert climate and thus have a more extensive distribution. The genus Lasallia is also umbilicate, but has a pustulate thallus, 1-spored asci and larger ascospores. Llano (1950) after Scholander (1934) proposed using 5 genera within the Umbilicariaceae, based in large measure on the superficial morphology of the apothecia (gyrose, omphalodisc, leiodisc, etc.). His classification was followed for some time in North America, but today two genera are universally accepted. With Umbilicariae it often helps to collect a range of different sized (and aged) individuals from a location so that the full developmental sequence can be interpreted. One frequently focuses on collecting larger sized specimens, that may no longer have all the structures found in younger thalli.