Acarosporaceae

Formerly classified in the fungal order Lecanorales, phylogenetic analyses in 1998 suggested that the Acarosporaceae belong outside this order;^[4] further analysis supported this conclusion.^[5] The Acarosporaceae is the most basal family in the division Lecanoromycetes.^[6]

Most members of the Acarosporaceae are lichenised, although a rare few are lichenicolous. The form of the thallus ranges from crustose to squamulose to peltate-somewhat umbilicate. The ascomata are in the form of apothecia, which are usually immersed in the thallus. They are typically lecanorine, although a few are biatorine, and Polysporina and Sarcogyne have lecideine apothecia. The photobiont partner is chlorococcoid (i.e., green algae from the family Chlorococcaceae). Various lichen products have been reported in the family, including depsides, depsidones, and derivatives of pulvinic acid. Most Acarosporaceae species grow on land or on rock.^[7]

Acarosporaceae species are found in a broad range of environments, from coastal areas to high mountain regions, although they are particularly abundant in arid and semi-arid habitats. They do not occur in tidal zones where lichens are periodically submerged, nor are they present in the deep shade of dense forests. While the family is absent from tropical ecosystems, its members are frequently encountered in arid regions, including parts of South Africa and the Andes of South America.^[8]

Many species within Acarosporaceae grow on calcareous or non-calcareous rock substrates, with some restricted to basic (HCl−) rock. Certain taxa, such as Acarospora nodulosa and A. schleicheri, are exclusively found in soil crusts. A few species can colonize wood; in Europe, A. similis is considered an obligate wood-dwelling lichen, whereas A. americana is the most frequently recorded on wood in North America. Some saxicolous species exhibit either facultative or obligate lichenicolous growth, beginning as non-lichenized parasites on host lichens and then developing into lichenized forms. One example is A. interjecta, which starts as a parasite on the yellow A. novomexicana before transitioning into a distinctive brown, fully lichenized thallus. A small number of species remain permanently lichenicolous without becoming lichenized, such as A. destructans, common in southern California, and A. lendermeri, which parasitizes Candelariella species in Asia and western North America.^[8]