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Verrucariales (subdivision Ascomycotina) An order of (mainly lichenized) fungi in which the thallus is usually crustose, sometimes foliose or squamulose, and grey to brown in colour. The ascocarps are perithecioid (see PERITHECIUM) and may be sessile or immersed in the thallus or substrate. There are several genera, found mainly on rocks, walls, etc.