Leucodermia leucomelos is a species of fruticose lichen in the family Physciaceae, and the type species of the genus Leucodermia. This species is widely distributed in tropical, subtropical, and warm temperate regions, where it grows on both trees and rock faces. The species forms pale, narrow branches 4–8 cm (1+5⁄8–3+1⁄8 in) long that divide repeatedly as they grow. The cream-coloured to whitish branches have distinctive long, dark hairs (cilia) along their edges, and typically grow in loose clusters on trees or rocks. It usually reproduces through powdery patches (soralia) on its lower surface, though it sometimes produces small disc-shaped fruiting bodies (apothecia). The species shows physiological adaptations to different light environments within the same habitat. Populations growing in shaded locations have higher protective mechanisms against sudden light exposure from sunflecks. Meanwhile, populations in sunny areas achieve higher rates of photosynthesis. This adaptability to varying light conditions appears to be an important factor in the species' widespread distribution across different forest types, allowing it to persist both in well-lit and deeply shaded locations while maintaining photosynthetic efficiency through specialized physiological responses. Chemical analysis shows that L. leucomelos contains several biologically active compounds, including atranorin, salazinic acid, and other substances that show antifungal properties. Carl Linnaeus first described the species in 1763. Since then, it has undergone multiple taxonomic revisions, including debates about the correct spelling of its name. It is now recognized as the type species of the genus Leucodermia. While widespread globally, it is considered a species of conservation concern in some regions, particularly in the Pacific Northwest of North America, where it is designated as a Sensitive Species by both the U.S. Forest Service and Bureau of Land Management.
Taxonomy It was originally described by Carl Linnaeus in 1763, as Lichen leucomelos. His diagnosis of the lichen was as follows (translated from Latin): "A linear, branched, slightly black-ciliated foliose lichen, with somewhat pedunculate, radiating peltate scales. Found in South America. Lobes branched at the base, linear with a diameter of one line, palm-sized, spreading, uneven, milky, smooth on top, slightly floury underneath, infrequently ciliated on the edge with longer black, somewhat branched hairs. The peltate scales are white, hemispherical, concave, pedunculated, and slightly radiated at the edge: with slender, white teeth." The holotype specimen of L. leucomelos is preserved in the Linnaean Herbarium (LINN 1273.109). The specimen, which was sent to Linnaeus from America (marked 'Amer.' by Linnaeus), formed the basis for his diagnostic phrase-name and description in 1763. On the type specimen sheet, Linnaeus himself wrote leucomelus, attempting to latinise the Greek black-white epithet. Two subspecies were recognized by T.D.V. Swinscow and Hildur Krog in 1976. Subspecies boryii was previously treated as a distinct species, Anaptychia neoleucomelaena, by Syo Kurokawa in 1961. Klaus Kalb also suggested recognizing this taxon at the species level. In 2023, Frank Bungartz formally established the new combination Leucodermia leucomelos f. albociliata, based on Anaptychia leucomelos f. albociliata Hue (1899). This form is characterized by its distinctive white cilia, in contrast to the typical black cilia of the species. While Kalb had illustrated this form in the 2015 paper establishing the genus Leucodermia, the combination had not been formally published at that time since no MycoBank number was registered for the forma albociliata.
Naming The scientific name Leucodermia leucomelos has a complex nomenclatural history. The specific epithet, derived from Greek elements meaning "white-black", has been subject to various spelling interpretations since Linnaeus first published it as leucomelos in 1763. On the type specimen sheet, Linnaeus wrote leucomelus, apparently attempting to latinise the Greek components. While some later authors used variants like leucomelaena or argued that leucomelos was a misprint for leucomelas (Greek for white-black), Linnaeus consistently used leucomelos in his publications, including Systema Naturae. A significant variation occurred when Erik Acharius introduced leucomela in his 1803 combination Parmelia leucomela. Though Salisbury's 1978 analysis argued for leucomelas as the correct form, nomenclatural specialists maintained that since Linnaeus's intended spelling could not be definitively proven, the original leucomelos must be retained under Article 73 of the International Code of Botanical Nomenclature. This spelling was formally proposed for conservation in 2012, and in 2017, the Nomenclature Committee for Fungi recommended its conservation with 70% support. The species has undergone multiple generic reassignments, being placed in Parmelia, Physcia, Borrera, Anaptychia, and Heterodermia before its current placement in Leucodermia. The generic name Leucodermia itself combines elements from the species' previous classification ("ser. leucomelaenae") with Heterodermia. In English, the species is known by the common names "elegant fringe lichen" and "elegant centipede," both referring to its characteristic appearance with long, dark marginal cilia.
Description
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