Verrucariaceae Verrucaria nigrescens f. nigrescens Growth type crustose. Chemical results negative. Very common on calcareous rocks, walls and mortar. In Europe recorded as host to Zwackhiomyces lithoiceae. Dark brown or blackish thallus minutely cracked into +/- smooth areoles with thick black hypothallus. The shiny black perithecia are half to three-quarters immersed. Asci double-walled, 8-spored, spores 17-28 x 8-14 µm. Verrucaria nigrescens f. tectorum develops green or olive-brown blastidia on the surface of the aureoles Similar: Verrucaria fusconigrescens and Verrucaria macrostoma.

Verrucaria nigrescens
Parkstone, Dorset. March 2012