Species: Rhizocarpon reductum
Photos: Co. Cork, SW Ireland. Specimen left identified by J. Douglass
Cracked-areolate, greyish to mousey-brown thallus with thin black prothallus. Black apothecia with thin, persistent margin, initially innate, becoming sessile. Dark green to greyish-brown epithecium. Asci 8-spored, spores muriform with 8-13 cells, 20-35 x 10-15 Ám, colourless. Microscope photographs below.
A pioneer species of siliceous rock, pebbles and tombstones.
Chemical reactions variable, usually K+ yellow, C-, P+ orange. Rarely K-, P- or K+ red, P+ orange.
Similar: Rhizocarpon lavatum. Chemical reactions negative.