Pertusaria xanthoisidiata
Pertusaria xanthoisidiata is a species of corticolous, crustose lichen in the family Pertusariaceae. Found on the Galápagos Islands, it was formally described as a new species in 2015 by Alan W. Archer, Frank Bungartz, and John Elix. The type specimen was collected on Pinta Island, where it was growing on an exposed trunk of Opuntia galapageia. The species epithet refers to the yellow-coloured isidia.
Description
Pertusaria xanthoisidiata forms a crust-like growth on tree bark. Its main body is a pale yellowish-green colour and can appear either dull or somewhat shiny. The surface is smooth and unwaxed, and whilst initially flat, it soon becomes densely covered with small, finger-like projections called isidia. These isidia are granular to cylindrical in shape, sometimes branching, and measure about 0.1–0.16 mm in width and 0.15–0.7 mm in height. Beneath the surface layer, the internal tissue is white throughout.The edges of the lichen may occasionally show faint circular zones and are typically bordered by a dark brownish margin called a. No reproductive structures, such as apothecia or pycnidia, have been observed in this species.
When tested with chemical spot tests, the surface layer is P−, K−, and C+. The internal tissue P+, K+, and C−. Under ultraviolet light, it may display a faint orange glow. Chemical analysis has revealed the presence of several secondary metabolites, including various forms of chlorolichexanthone, arthothelin, and several stictic acids.