Lepraria sylvicola

This species forms a powdery, crust-like growth (the thallus) that appears bluish-white to pale blue-grey in colour. The thallus has a distinctive powdery texture made up of tiny granules measuring between 40 and 160 micrometres in diameter. Unlike some related species, it lacks an inner layer (medulla). Beneath the main body of the lichen, there are usually sparse fungal threads (hyphae) that range from white to pale orange-brown in colour. When tested with common chemical reagents used in lichen spot tests, the thallus shows characteristic reactions: it turns yellow or shows no reaction with PD, becomes yellowish with K, and shows no reaction with C. Under ultraviolet light (UV), it shows no fluorescence. The underlying fungal threads turn purple-red when treated with K. Chemical analysis has revealed several major secondary metabolites in this species, including roccellic acid, toensbergianic acid, and atranorin, along with minor amounts of anthraquinone pigments found only in the underlying fungal threads. The presence of roccellic acid was confirmed through mass spectrometry analysis of a specimen. Scientists note that another compound, angardianic acid, might also be present but cannot be distinguished from roccellic acid using standard identification techniques (thin-layer chromatography). …

Lepraria sylvicola is found throughout western Britain, including Wales, northern England, and western Scotland, as well as in Ireland. The lichen shows a strong preference for tree bark that is neutral to slightly acidic in pH. It is especially common on mature sessile oak (Quercus petraea) in natural and semi-natural woodlands. While oak is its primary substrate, it can also be found growing on other tree species including alder (Alnus glutinosa), downy birch (Betula pubescens), ash (Fraxinus excelsior), and rowan (Sorbus aucuparia). Occasionally, it can be found growing on rock surfaces, particularly in areas sheltered from direct rainfall and on slightly calcareous siliceous rock. It has also been reported from France. The species occurs at elevations ranging from near sea level (10 metres) up to 440 metres above sea level, and can be locally abundant within its preferred habitats. In western British oak woodlands, it is often the dominant Lepraria species, typically growing on the rain-sheltered sides of tree trunks and large branches. It frequently grows alongside the moss Isothecium myosuroides, forming distinctive ecological communities. In areas where its coverage is less extensive, the lichen can be found as part of diverse communities on sessile oak that include several rare or notable species from the Lobarion pulmonariae alliance. …