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Verrucaria margacea (Wahlenb.) Wahlenb.
Family: Verrucariaceae
[Involucrothele margacea (Wahlenb.) Servít,  more]
Verrucaria margacea image
Lucy Taylor  
Thallus: continuous or broken up, thinning at margin, irregularly rimose to areolate especially in fertile parts, thin (less than 0.1 mm), subgelatinous when wet, lacking a black basal layer areoles: plane, 0.3-0.5 mm wide surface: dark olive gray to greenish brown, smooth, dull anatomy: paraplectenchymatous throughout but without a discernible upper cortex, algal cells 6-10 µm in diam., densely packed, filling most of the thallus Perithecia: immersed in lens-shaped to hemispherical swellings of the thallus with apices slightly emergent or with a broader upper part naked; exciple: subglobose, 0.20-0.35 mm wide, pale brown, darker around apex, c. 20 µm thick; involucrellum: extending (almost) down to the base-level of the perithecium, contiguous with the exciple or slightly diverging (with inner parts paler), 40-80 µm thick, pigmentation of "Zellnetztyp"; periphyses 25-35 µm long, 2-3 µm thick, simple asci: clavate, 80-100 x 20-30 µm, 8-spored ascospores: hyaline, simple, ellipsoid, (22-)25-35 x 10-14 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, on inundated or periodically submerged siliceous rocks World distribution: Europe, Asia, North America, New Guinea, Australia, and New Zealand Sonoran distribution: montane areas of Arizona and southern California. Notes: Within the freshwater species occurring in the region Verrucaria margacea has the largest spores. The involucrellum is variable and may be almost as thin and wide spreading as in Verrucaria hydrela, but the latter species has both smaller perithecia and spores.