Pachnolepia

Species of Pachnolepia form crustose lichens with distinctive morphological features. The thallus is typically effuse (spread out on the substrate), continuous, and can be whitish to pale grey or pale brown in colour. Surface texture varies from matt or powdery to somewhat verrucose, with thickness ranging from very thin (< 0.1 mm) to occasionally warty and up to 1 mm thick. The genus includes both fertile and sterile species.^[8][7]

When present, apothecia are up to 1 mm in diameter, rounded or angular, and may be elongated or somewhat stellate. They are characteristically immersed in the thallus and often appear inconspicuous when dry due to thick white pruina. The internal structure includes a red-brown epithecium that turns grey or pale green in potassium hydroxide solution (K), a colourless hymenium 40–60 μm tall, and numerous paraphysoids. Ascospores, when present, are cylindric to obovoid in shape, and usually contain 4 or 5 septa. They are colourless (hyaline) and measure 13–22 by 4.5–7 μm.^[8]

Some species produce reproductive structures other than apothecia, such as pseudoisidia, which can be cylindrical to gnarled and unbranched. The photobiont is trentepohlioid across the genus.^[7]

Members of the genus Pachnolepia are corticolous, growing on the bark of trees. In Europe, P. pruinata shows a preference for rain-sheltered, dry bark of tree trunks in nutrient-enriched situations, particularly favouring species such as Maple, Ash, and Oak. It can become locally dominant on tree trunks and is occasionally found on wooden boards and dry stonework. The species is frequent in southern Britain, extending locally to southern Aberdeenshire, while being uncommon and primarily eastern in distribution in Ireland.^[8]

In South America, P. longipseudisidiata has been documented in mountain forest habitats of Brazil, specifically in the Chapada Diamantina region, where it occurs at elevations of around 1,100 m (3,600 ft).^[7]