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. Verrucaria nigrescens f. tectorum develops green or olive-brown blastidia on the surface of the aureoles Very common throughout Ireland on calcareous rocks, walls and mortar, rare on acidic rocks. Chemical reactions negative. Lichenicolous fungi include Opegrapha opaca, Skyttea spinosa, Endococcus propinquus, Stigmidium clauzadei and Zwackhiomyces lithoiceae

     


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