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DescriptionLife habit: lichenized, few species lichenicolous.; Thallus: crustose endosubstratic or superficial, indistinct to rather thick, continuous or rimose to areolate, sometimes subsquamulose or granular (of goniocysts), when superficial fully attached with lower surface or with basally constricted areolae, rarely by stipe-like holdfasts; margin determinate or indeterminate, prothallus usually dark, entire or fimbriate, or not apparent; surface: white, gray, ochraceous, green, shades of brown to black, dull or shiny, even or variously rugose, very rarely isidiate-pseudosorediate; upper cortex: paraplectenchymatous of small roundishangular cells, or indiscernible to lacking, often overlain by an amorphous hyaline layer deriving from dead collapsed cortical cells; medulla: (sub)paraplectenchymatous or with filamentous parts, in endolithic species of filamentous hyphae penetrating the disintegrated rock (pseudomedulla); photobiont: primary one various (Coccobotrys, Dilabifilum, Heterococcus, Myrmecia a. o.), secondary photobiont absent; algal cells usually distributed over most of the thallus or concentrated in an upper zone to leave an alga-free medullary layer, algal cells in vertical rows or in clumps or irregularly dispersed; lower cortex: lacking (rarely marginally developed in subsquamulose species); Ascomata: perithecial, immersed in the substratum or in the thallus or thalline warts or erumpent to superficial, laminal or lateral (between areoles), globose or broadly ovoid or pear- to bottle-shaped; exciple: colorless, brown or black; involucrellum: present or absent, often carbonaceous and brittle; interascal filaments absent (gelatinizing early, lacking in mature perithecia); ostiolar filaments: present, simple or sparingly branched or ramified-anastomosing; hymenial gel I+ bluegreen or reddish; asci: clavate, fissitunicate, thin-walled, wall not amyloid, apically not or slightly thickened, 8-spored; ascospores: biseriate, subglobose, ellipsoid, ovoid or subfusiform, thin-walled (thick-walled in some species of uncertain affinity), simple, hyaline, not sculptured, rarely halonate, in some species with a thin perispore; Conidiomata: pycnidial, laminal, immersed, of Staurothele-type (Harada 1993); conidia: cylindrical, straight or slightly bent; Secondary metabolites: absent.; Geography: world-wide, mainly in warm-temperate to arctic-alpine regions; Substrate: mostly rock (calcareous or siliceous), rarer bark or soil, on dry places or periodically inundated or submerged in maritime or freshwater habitats.; Notes: In this volume Bagliettoa is excluded from Verrucaria. Otherwise, Verrucaria is treated in a traditional circumscription. Recent molecular analyses have shown that the genus is highly heterogeneous (Gueidan et al. 2007). A few of the species treated have already been split off from Verrucaria (Navarro-Rosines et al. 2007) and the segregation of others will follow in forthcoming papers. But at the time being, in this survey, it is too early to follow new cladistic concepts as the relationships of the majority of the species and species groups is not yet understood. With 61 species, Verrucaria is comparatively well represented in the Sonoran region, but many species are known only from few collections. Sonoran Verrucaria species mostly represent Northern Hemisphere distribution patterns; only eight species have wider ranges extending to the southern continents. Verrucaria calkinsiana and V. finkiana have scattered occurrences in North America. Restricted to southwestern North America are Verrucaria americana, V. bernardinensis, V. cetera, V. inficiens, V, rubrocincta, V. rupicola, and V. subdivisa. Verrucaria dacryodes is endemic to California. Of the seven newly described species, four are from Arizona, and one from California. 24 species (Verrucaria adelminienii, V. asperula, V. beltraminiana, V. bernaicensis, V. confluens, V. elaeina, V. endocarpoides, V. floerkeana, V. fraudulosa, V. fusca, V. fuscoatroides, V. inornata, V. memnonia, V. mimicrans, V. minor, V. murorum, V. nigrofusca, V. olivacella, V. onegensis, V. prosoplectenchymatica, V. rufofuscella, V. schindleri, V. turgida, and V. weddellii) are reported for the first time from the North American continent. For determination, careful sectioning of well developed perithecia are necessary. To understand the variability of the involucrellum, cuts straight through the ostiole of several well-developed perithecia covering the full range of size, development, and grade of exposure are necessary. According to the pigmentation, two types of involucrellum can be distinguished: in the common type the pigmentation occurs in flecks between the cells, thus obscuring the outline of the cells. In an involucrellum of the so-called "Zellnetztyp", the pigmentation is clearly restricted to the cell walls so that the outlines of the pigmented cells are clearly visible in thin sections. The latter type is primarily found in freshwater species. The lengths of periphyses are taken from the middle of the periphysal cushions, omitting the shortest ones around the ostiolum and those immediately above the ascal region. In perithecia with a distinct apical neck the periphyses in the ostiolar neck may differ in length and branching from those further down, and then are described separately. For spore sizes, only mature and well-developed spores (spores released from the asci, not those containing large vacuoles or empty ones) are measured. This is important as the magnitudinal ranges of spores given in the literature for many species is too wide. The spore-measurements given in the key comprise the normal range without the extremes. In several species the lower zone of the thallus is conspicuously blackened (sometimes carbonaceous); this is referred to as "black basal layer" contrary to the term "medulla" which is used for a colorless or browning, alga-free layer under the algal layer. The maritime species are not treated here, but see Collemopsidium (Vol. I, p. 162).