A well-identifiable Peltigera species, characterized by the flat rounded horizontal apothecia, and dark fasciculate rhizines in concentric circles. The lichen prefers forest environment and humid habitats. Sometimes, it is even recognized as an indicator species of localities with a longstanding forest continuity. It inhabits bases of older trees, logs, mossy stones and rocks and soil in both acidic and calcareous biotopes. In the Czech Republic, the species occurs sparsely from lowlands to mountains with the centre of distribution in mountain and submountain areas. During the 20th century, P. horizontalis declined in the country, probably in consequence of acid rain and changes in landscape management (Liška et al. 2006). In Europe, it is one of the common genus members, occurring mainly in mountains and rather oceanic parts of the continent.
Literature: Liška J., Palice Z., Dětinský R. & Vondrák J. (2006): Changes in distribution of rare and threatened lichens in the Czech Republic II. – In: Lackovičová A., Guttová A., Lisická E. & Lizoň P. [eds], Central European lichens – diversity and threat, p. 241–258, Mycotaxon Ltd., Ithaca.taxonomic classification:
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