Order: Verrucariales       Family: Verrucariaceae Species: Verrucaria nigrescens Growth type crustose. Photos: On churchyard memorial. Macroom, Cork, SW Ireland. Dark brown to blackish thallus regularly cracked into +/- smooth areoles, occasionally with blastidiate margins. Perithecia half to three-quarters immersed. Prothallus inconspicuous or absent. Asci are double-walled, 8-spored, spores 17-28 x 8-14 µm. Very common throughout Ireland on calcareous rocks, walls and mortar, rare on acidic rocks. Chemical reactions negative. Similar: Verrucaria nigrescens f. tectorum develops green or olive-brown blastidia on the surface of the aureoles

     


Verrucaria nigrescens. Protestant churchyard, Macroom, Co.Cork. December 2008