Pertusaria flavida
Pertusaria flavida is a species of corticolous crustose lichen in the family Pertusariaceae. First described in 1815, it is characterized by its distinctive pale to bright sulphur yellow or yellow-green-grey thallus with a cracked, warted surface. The lichen reproduces mainly through small spherical or cylindrical outgrowths called isidia, which occasionally break down into powdery structures, while fruiting bodies are very rare. It contains thiophaninic acid, giving it an orange fluorescence under ultraviolet light. Widespread throughout southern and eastern Britain, parts of Wales, Scotland, and Ireland, as well as mountainous regions of Spain and Portugal, P. flavida typically inhabits the bark of mature broad-leaved trees in well-lit environments such as open woodlands, parklands, and roadside trees.
Taxonomy
It was first formally described as a new species by Augustin Pyramus de Candolle in 1815 as Variolaria flavida. Jack Laundon transferred it to the genus Pertusaria in 1963.Description
Pertusaria flavida has a distinctive pale or bright sulphur yellow to yellow-green-grey or yellow-brown thallus. The thallus occasionally has a pale to dark grey margin and is characteristically rather thick and uneven, with a more or less coarsely appearance. The upper surface of the thallus is coarsely warted, flat, smooth, or somewhat roughened in texture. A distinctive feature of this species is the numerous isidia, which are more or less spherical or shortly cylindrical- in shape. These isidia occasionally dissolve into soredia, sometimes obscuring the thallus entirely. When shed, these structures leave faint cortical scars on the thallus surface.Apothecia are very rare in this species. When present, approximately 2–5 apothecia are immersed within hemispherical warts that are sorediate-isidiate. The of the apothecium is black-brown and . The asci contain 8 spores each. The measure 60–100 by 25–40 μm, with a wall thickness of 7–10 μm, becoming less than 20 μm thick at the ends.
Chemical spot tests reveal that the thallus is C+ and KC+, K–, and Pd–. Under ultraviolet light, the thallus fluoresces bright orange or yellow-orange, indicating the presence of thiophaninic acid and an unidentified secondary metabolite.