Chrysothrix Pavonii

''Chrysothrix'' is a genus of lichen-forming fungi in the family Chrysotrichaceae. They are commonly called gold dust lichens or sulfur dust lichens,Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, because they are bright yellow to greenish-yellow, sometimes flecked with orange, and composed entirely of powdery soredia.Brodo, I. M., S. D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. Yale University Press: New Haven. 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. Uphof, J. C. T. 1959. Dictionary of Economic Plants. Hafner Publishing Co.: New York.

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 () and (), 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 earlier validly published name, ''Peribotryon pavonii'', described by Elias Magnus Fries in 1832. Therefore, Laundon established ''Chrysothrix pavonii'' as the correct name for this species, honoring its original collector, José Antonio Pavón Jiménez.

Laundon's revision also addressed issues of nomenclatural stability. Although ''Pulveraria'', described by Erik Acharius in 1803, technically predated ''Chrysothrix'', this name had fallen out of use since 1886 and was based on a sterile lichen, making it difficult to apply accurately. Recognizing the importance of maintaining stability in lichen nomenclature, Laundon successfully proposed conserving ''Chrysothrix'' over the earlier name ''Pulveraria''. Additionally, in 2012, he formally proposed conserving ''Chrysothrix'' against another older name, ''Alysphaeria'', published in 1827. The Nomenclature Committee for Fungi accepted this proposal in 2017, further solidifying ''Chrysothrix'' as the accepted genus name despite these historical complexities.

Description

The genus ''Chrysothrix'' is characterized by its bright yellow to yellow-green, powdery () lichens. Its thallus, or body, is usually or filamentous, appearing crust-like or fluffy, without a clear margin or . These lichens are non-layered and uniformly colored throughout due to the presence of pulvinic acid derivatives, substances responsible for their vivid pigmentation. The specific compounds identified in ''Chrysothrix'' include calycin, pinastric acid, rhizocarpic acid, and vulpinic acid, which also assist in protecting the lichens from herbivory.

Microscopically, ''Chrysothrix'' consists of branched and interwoven hyphae (fungal filaments), often bearing small crystals. The algae partners within the lichens are green algae ( Chlorophyceae), with spherical cells usually occurring individually or grouped.

Reproductive structures (apothecia) in this genus are uncommon and usually small, with diameters reaching up to about 2 mm. When present, these apothecia are typically circular or spherical, with poorly defined margins, and range in color from greenish-yellow to brownish-orange, often obscured by a yellowish powder. The internal structure includes loosely interwoven fungal filaments forming the and a distinct upper layer () of extensively branched and interconnected filaments ( paraphyses). The spores are typically narrow, elongated, clear, and divided into four segments by three transverse septa.

Habitat and distribution

''Chrysothrix'' species have a wide distribution, found globally except in major desert regions and polar extremes. They commonly inhabit shaded, acidic substrates such as tree bark, decaying wood, and rock surfaces, typically favoring environments shielded from intense sunlight and areas free from nitrogenous pollution. Specific habitat preferences vary among species, with some adapted to oceanic climates in Western Europe and others growing predominantly in boreal or tropical regions. The genus occurs from low to moderate altitudes, although some species are adapted to high-altitude environments, reaching elevations up to approximately 3,350 meters. Seven ''Chrysothrix'' species occur in Australia.

Species

*'' Chrysothrix bergeri'' – southeastern United States; the Caribbean; Bermuda
*'' Chrysothrix caesia'' – Europe; North America
*'' Chrysothrix candelaris'' – Europe; North America
*'' Chrysothrix chamaecyparicola'' – eastern North America
*'' Chrysothrix chilensis'' – Chile
*'' Chrysothrix chlorina''
*'' Chrysothrix chrysophthalma'' – Europe
*'' Chrysothrix citrinella'' – Brazil
*'' Chrysothrix fagicola'' – Europe
*'' Chrysothrix flavovirens''
*'' Chrysothrix frischii''
*'' Chrysothrix galapagoana''
*'' Chrysothrix granulosa'' – South America
*'' Chrysothrix insulizans'' – United States
*'' Chrysothrix occidentalis'' – Australia
*'' Chrysothrix onokoensis'' – United States
*'' Chrysothrix palaeophila'' – Australia
*'' Chrysothrix pavonii''
*'' Chrysothrix placodioides'' – South America
*'' Chrysothrix septemseptata'' – India
*'' Chrysothrix susquehannensis'' – eastern North America
*'' Chrysothrix tchupalensis'' – Australia
*'' Chrysothrix xanthina'' – widespread

The taxon ''Chrysothrix oceanica'', proposed by Veli Räsänen in 1944 from a single specimen collected in Fiji, was excluded from the genus by Laundon. Because of the presence of pulvinic acid derivatives in the specimen, he suggested it might belong in '' Caloplaca''.

References

{{Taxonbar , from1=Q15644212 , from2=Q108894528

Arthoniomycetes genera
Lichen genera
Taxa described in 1852
Taxa named by Camille Montagne