Ochrolechia arborea (Kreyer) Almb.

Practically always sterile, grey-white lichen with yellowish, greenish or creamy, mainly delimited soralia, which may gradually merge with the age. Within the genus, the species resembles e.g. members of O. androgyna agg. but usually has smaller thalli and soralia. Some sorediate Lecanora species, such as L. impudens or L. variolascens, may also look very similar. In the field (without closer examination), confusion with some morphotypes of Phlyctis argena cannot be ruled out. Ochrolechia arborea is, however, relatively easily to identify chemically by spot reactions and using a UV lamp, as it contains a combination of two positively reacting substances, gyrophoric acid and chloroxanthone (C+ red, UV+ orange).

The lichen usually grows epiphytically on a variety of substrates, on a lit bark of conifers and deciduous trees, on both old trunks and thin twigs. Its occurrence on wood is not exceptional. However, in the Czech Republic, its occurrence on deciduous trees predominates. Ochrolechia arborea is a relatively inconspicuous, easily overlooked or confusable lichen, especially if it occurs as a pioneer in a form of young thalli and is not collected and studied chemically. According to the current data, its Czech distribution and abundance have been almost certainly underestimated. The species seems to have the potential to successfully spread newly. Occasionally, it is recorded on twigs of trees and shrubs at forest edges or in field spinneys (blackthorns, hawthorns, etc.). These are specific habitats recolonised in recent decades by rich and diverse lichen communities. In the Czech Republic, the lichen has also been found on rocks.

Literature: Tønsberg T. (1992): The sorediate and isidiate, corticolous, crustose lichens in Norway. – Sommerfeltia 14: 1–331. Kukwa M. (2009): The lichen genus Ochrolechia in Poland III with a key and notes on some taxa. – Herzogia 22: 43–66.

Ascomycota → Lecanoromycetes → Pertusariales → Ochrolechiaceae → Ochrolechia