The Physciaceae are a family of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. A 2016 estimate placed 19 genera and 601 species in the family.
Taxonomy
Physciaceae was formalised by Alexander Zahlbruckner in Adolf Engler's Syllabus (1898), with Physcia as the type genus. In a set of conservation proposals intended to stabilise long-used family names, Hawksworth and Eriksson (1988) recommended conserving Physciaceae against the earlier name Pyxinaceae (basionym: "trib." Pyxineae E.M.Fries, 1825), arguing that Pyxinaceae had not been taken up in standard works and that Physciaceae was firmly established in the literature. They characterised Physciaceae as one of the major families of the Lecanorales, then comprising about 20 genera and roughly 850 species, many of them familiar macrolichens.
Hawksworth and Eriksson also noted historical alternatives that do not displace Physciaceae: Körber's "Anaptychiaceae" (attributed to Massalongo) proved to be a tribal-rank usage without a diagnosis, so it was not validly published; had it been valid and pre-1898, it would likewise have required conservation of Physciaceae over that name.
Description
The Physiaceae includes various growth forms such as foliose, fruticose, squamulose, stipitate, crustose, and even evanescent types (where certain parts, such as basal squamules, become less noticeable or disappear over time as other structures develop). Some members of this family may also be lichenicolous, meaning they grow on other lichens. These lichens can exhibit features such as lobules, isidia, and soredia, or may lack them entirely.
The upper cortex of Physiaceae lichens can be prosoplectenchymatous, paraplectenchymatous, or absent. Their photobiont, or the symbiotic algae living within the lichen, is typically a unicellular green alga from the genus Trebouxia, with a diameter ranging from 5 to 20 μm. The medulla can vary from poorly to well-developed or may even be...
