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Verrucaria macrostoma Dufour ex DC.
Family: Verrucariaceae
Verrucaria macrostoma image
André Aptroot  
Thallus: cracked-areolate, up to several cm wide, 0.3-0.6 mm thick, with broad fissures, without black basal layer areoles: angular to irregular in outline, plane or slightly convex, 0.5-1 mm wide, with pale to brown flanks surface: pale to dark brown, dull, smooth to somewhat uneven anatomy: upper cortex: paraplectenchymatous, 20-30 µm thick, composed of ±round angular cells 4-6 µm in diam., with a brown uppermost cell layer sometimes overlain by an amorphous, hyaline epinecral layer up to 15 µm thick; algal layer: paraplectenchymatous, with mycobiont cells 5-8 µm in diam., with algal cells 5-8 µm in diam.; medulla: subparaplectenchymatous, colorless to pale brown in patches, ±interspersed with substrate particles, lowest part with a looser texture grading into hypothalline hyphae penetrating the decomposed rock surface Perithecia: fully immersed within areoles or with slightly emergent tips, basal part often sunken in shallow pits in the rock; exciple: broadly pyriform, colorless to dark brown, 0.3-0.4 mm wide, c. 25 µm thick; involucrellum: appressed to the exciple, encircling approx. the upper third, rarely reaching the middle of the perithecium, base often diffuse, merging with brown patches of the medulla; periphyses 35-45 µm long, 3-4 µm thick, branched-anastomosing asci: clavate, 85-105 x 25-30 µm, 8-spored ascospores: hyaline, simple, ellipsoid, 20-28 x 10-13 µm Pycnidia: immersed, 50-100 µm across conidia: cylindrical, c. 4 x 1 µm. Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, usually on limestone, one record from rhyolite, on nutrient-enriched surfaces, montane World distribution: Europe, North Africa, and North America Sonoran distribution: Arizona (Gila, and Maricopa Counties), southern California (Santa Monica Range), and Sonora. Notes: Similar specimens with deeper reaching involucrellum and larger spores refer to Verrucaria murorum. Verrucaria viridula comes close in overall appearance but differs in larger, distinctly pear- to bottle-shaped perithecia, larger spores and longer periphyses.