Leprocaulon Calcicola

''Leprocaulon'' is a genus of lichen-forming fungi in the family Leprocaulaceae. Members of the genus ''Leprocaulon'' are commonly called cottonthread lichens. These small lichens typically form soft, powdery coatings on their growing surfaces, sometimes developing tiny white thread-like structures that create a cottony appearance. The genus contains eleven recognised species found primarily in North America and Europe.

Taxonomy

The genus Leprocaulon was established by the Finnish lichenologist William Nylander and published by Edmond Lamy in 1879. The genus was circumscribed in Lamy's "Reasoned catalogue of the lichens of Mont-Dore and Haute-Vienne" (''Catalogue raisonné des lichens du Mont-Dore et de la Haute-Vienne'') published in the ''Bulletin de la Société Botanique de France'' in 1878, though the publication year of the genus indicates 1879. The genus name was apparently communicated by Nylander to Lamy through correspondence, as Nylander had not formally published the name ''Leprocaulon'' himself, but had merely noted in 1876 that ''Stereocaulon nanum'' was not a true ''Stereocaulon'' but resembled "a peculiar ''Lepraria''".

The type species is ''Leprocaulon nanum'', which was originally based on ''Lichen nanus'' described by Erik Acharius. According to Lamy's original description, ''Leprocaulon'' is characterised by small, delicate stems that may be or branched, sometimes partially denuded, with whitish powdery . The yellowing of the thallus when treated with potassium hydroxide serves as a diagnostic feature that distinguishes this genus from the closely related ''Stereocaulon''—a reaction that is characteristically absent in ''Leprocaulon'' species.

Prior to the establishment of ''Leprocaulon'', Theodor Magnus Fries had recognised the distinctive nature of these species in 1857 when he placed them in a separate section of ''Stereocaulon'' called sect. ''Chondrocaulon'', distinguished by their cartilaginous pseudopodetia and granular that typically break down into powdery particles. However, since ''Chondrocaulon'' was published only at sectional rank, Nylander's later generic name ''Leprocaulon'' takes nomenclatural precedence.

Description

''Leprocaulon'' species begin as a soft, diffuse coat of microscopic —technically called a leprose primary thallus—that spreads across the substrate like a pale dusting of powder. This layer lacks the organised upper and lower "skin" () seen in many lichens, giving it a loose, felt-like texture. In some species the develops a delicate secondary structure: countless white, thread-thin stems () that stand upright, branch repeatedly and weave together into a tiny, cottony turf. The cylindrical pseudopodetia have a slightly texture and are densely covered with the same powdery reproductive structures—soredia and tomentum—that coat the base. The internal photosynthetic partner is a green alga of the genus ''Trebouxia''.

Fertile populations of ''Leprocaulon'' produce small, rimmed discs ( apothecia) whose internal anatomy matches the ''Catillaria''-type: eight-spored asci with an outer iodine-positive layer and colourless (hyaline), septate spores. Asexual pycnidia have not been observed. Chemically the genus is diverse; thin-layer chromatography reveals an array of depsides, depsidones, phloroglucinol pigments, triterpenoids and fatty acids, although the exact profile varies between species and may aid identification when morphology alone is ambiguous.

Species

, Species Fungorum (in the Catalogue of Life) accepts 11 species of ''Leprocaulon'':
*'' Leprocaulon adhaerens''
*'' Leprocaulon americanum''
*'' Leprocaulon beechingii'' – eastern North America
*'' Leprocaulon calcicola'' – Great Britain
*'' Leprocaulon coriense''
*'' Leprocaulon inexpectatum'' – Italy
*'' Leprocaulon knudsenii'' – mountain ranges of central and southern California, USA
*'' Leprocaulon nicholsiae''
*'' Leprocaulon santamonicae''
*'' Leprocaulon terricola''
*'' Leprocaulon textum''

References

{{Taxonbar, from=Q10557809

Leprocaulales
Lecanoromycetes genera
Lichen genera
Taxa named by William Nylander (botanist)
Taxa described in 1879