Verrucaria macrostoma (images of British lichens)

Thallus cracked-areolate or subsquamulose, olive-green or shades of brown, 'looking like dried mud' (Dobson), prothallus indistinct, isidia or soredia sometimes present on the areolar margins; perithecia half-projecting above the surfaces of the areoles. On hard limestones, concrete, mortar of walls and other calcareous substrates, widespread but predominantly in the south and east.

Refs: Smith et al. (2009), 950; Purvis et al. (1992), 638; Orange (2008); Dobson (2005), 456 (photo); Dobson (2011), 463 (photo); Whelan (2011), 150 (photo); van Herk & Aptroot (2004), 382-3 (photo, f. furfuracea).

Can be confused with Acarospora species, notably A. fuscata, but Acarospora species have apothecia (generally inconspicuous and sunken, commonly angular) rather than perithecia.

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Images of British Lichens