Ochrolechia africana, commonly known as the frosty saucer lichen, is a species of crustose and corticolous (bark-dwelling) lichen in the family Ochrolechiaceae. It is a widely distributed species, found in tropical and subtropical areas of southern Africa, Asia, Australia, North America, and South America. The lichen is characterized by the presence of a white "frosty" or powdery apothecia.
Ochrolechia africana
UV-illuminated thallus and apothecia of Ochrolechia africana; the yellowish colour results from the fluorescence of lichexanthone.
Lichexanthone is an organic compound in the structural class of chemicals known as xanthones. Lichexanthone was first isolated and identified by Japanese chemists from a species of leafy lichen in the 1940s. The compound is known to occur in many lichens, and it is important in the taxonomy of species in several genera, such as Pertusaria and Pyxine. More than a dozen lichen species have a variation of the word lichexanthone incorporated as part of their binomial name. The presence of lichexanthone in lichens causes them to fluoresce a greenish-yellow colour under long-wavelength UV light; this feature is used to help identify some species. Lichexanthone is also found in several plants, and some species of fungi that do not form lichens.
UV-illuminated thallus and apothecia of the crustose lichen Ochrolechia africana; the yellowish colour results from the fluorescence of lichexanthone.
Part of a proposed biosynthetic pathway for lichexanthone-type lichen xanthones, depicting an aldol cyclization step followed by a cyclodehydration, which would lead to norlichexanthone.
Parmelina quercina is one of the first lichens from which lichexanthone was isolated.
Image: Minquartia guianensis 1zz
