Chrysothrix is a genus of lichen-forming fungi in the family Chrysotrichaceae. They are commonly called gold dust lichens or sulfur dust lichens, because they are bright yellow to greenish-yellow, sometimes flecked with orange, and composed entirely of powdery soredia. Apothecia are never present in North American specimens.
They grow on bark or rocks, generally in shaded habitats. They can sometimes be mistaken for sterile specimens of Chaenotheca, which usually has pinhead apothecia on tiny stalks, or Psilolechia, which usually has small, bright yellow apothecia. Chrysothrix chlorina was traditionally used as a brown dye for wool in Scandinavia.
Taxonomy
The genus Chrysothrix was circumscribed by the French botanist Camille Montagne in 1852, initially with only a single species, Chrysothrix noli-tangere, recognized for its distinctive growth on cactus spines in South America. Montagne named the genus from the Greek words chrysos ('golden') and thrix ('hair'), referring to the bright yellow, hair-like appearance of the lichens.
Historically, Chrysothrix was regarded as a monotypic genus, until Jack Laundon's comprehensive revision in 1981 expanded the genus significantly. Laundon discovered that several yellow, powdery lichens previously classified under other genera, such as Lepraria, Pulveraria, and Crocynia, shared critical anatomical features with Chrysothrix, particularly the structure of their apothecia (lichen fruiting bodies). Consequently, he reclassified several species, increasing the genus to four distinct species: C. candelaris, C. chlorina, C. chrysophthalma, and C. pavonii.
The type species was originally listed as Chrysothrix noli-tangere due to Montagne’s original description. However, Laundon clarified the taxonomic history in 1981, explaining that the name C. noli-tangere was illegitimate because its original description (as Cilicia noli-tangere by Montagne in 1834) included reference to an...
