Rhizocarpon geographicum (L.) DC. subsp. geographicum

     Thallus crustose which may form mosaics, smooth, continuous, strongly adherent to its substrate, areolate, areoles angular, 0.5-1.5 mm, flat or slightly convex, dull, greenish-yellow, yellow, bright yellow, hypothallus black very visible at the margin as well as between the areoles. Apothecia more or less numerous, coming into or between the areoles, 0.5-1.5 mm in diameter, round or slightly deformed, disk flat to weakly convex, black, thin margin inconspicuous even at first. Wine-colored epithecium in KOH. Submuriform spores with 5-8 cells visible in optical section, olive-brown (in KOH), 20-34 x 9-16 µm according to the literature, 20-30 x 11-15 µm according to our measurements. Photobiont: Chlorococcal. Cortex: C- or C+/- pink, K-, KC-, P- or P+/- yellow. The most common of the subsp. coming everywhere on the siliceous rocks.

N.B. Often parasitized by Schaeria fuscocinerea (among others) in our prospecting area.

N.B. Often also parasitized by many species of lichenicolous fungi.