Rhizocarpon subgeminatum Eitner

Rhizocarpon subgeminatum forms up to 10 cm large thalli with a conspicuous black prothallus. Its brown areoles are usually closely packed, giving the impression of a continuous thallus, but might also be dispersed. Apothecia are black with a strong proper persistent margin and one or two (sometimes four) hyaline muriform spores in asci. The olive-green epithecium is K-, in contrast to R. geminatum, which is K+ purple.

In central Europe, R. subgeminatum is more common in the eastern Alps (Nimis et al. 2018), otherwise it is rare. It is usually found on exposed siliceous nutrient-enriched rocks and stones, often at brook or lake shores, at higher elevations. In the Czech Republic, it was recorded at less than ten localities at middle elevations, mostly in the last century. Its distribution was summarized by Šoun et al. (2006). Recently, it has been collected in the Český ráj, Kokořín region and more localities in the Žďárské vrchy highlands.

Its first record from the area of the Czech Republic is interesting but has long been overlooked. An old revised specimen of J. Flotow from the Obří důl corrie in the Krkonoše Mts, probably from the first half of the 19th century, was noted in the paper where the species was first described (Eitner 1911). It was hidden in a note included in the description of R. pseudorivulare, which was later synonymized.

Literature: Eitner E. (1911): Dritter Nachtrag zur schlesischen Flechtenflora. – Jahresbericht der Schlesischen Gesellschaft für Vaterländische Kultur, Abt. Zool.-Bot., Breslau, 88: 20–60. Šoun J. et al. (2006): Lišejníky zaznamenané během 16. bryologicko-lichenologických dnů v Kameničkách (CHKO Žďárské vrchy, 2.–5.10.2003). – Bryonora 38: 39–47. Nimis P. L., Hafellner J., Roux C., Clerc P., Mayrhofer H., Martellos S. & Bilovitz P. O. (2018): The lichens of the Alps – an annotated checklist. – Mycokeys 31: 1–634.

Ascomycota → Lecanoromycetes → Rhizocarpales → Rhizocarpaceae → Rhizocarpon