Psora Crenata

''Psora'' is a genus of lichen-forming fungi in the family Psoraceae. Members of the genus are List of common names of lichen genera, commonly called fishscale lichens.USDA Natural Resources Conservation Service Name Search
/ref> Lichens in the genus ''Psora'' generally have a Squamulose lichen, squamulose thallus and anthraquinones in the hymenium. partners of ''Psora'' lichens include members of the green algal genera ''Asterochloris'', ''Chloroidium'', ''Myrmecia (alga), Myrmecia'', and ''Trebouxia''.

Taxonomy

The genus ''Psora'' was first validly published name, validly published in 1796 by the German lichenologist Georg Franz Hoffmann. His of the genus was brief: "Crust patterned. Scutellae (small shields) bordered, convex.") He included 26 species in the genus.

Description

Genus ''Psora'' comprises lichens recognised for their relatively large, thick , which are the leaf-like structures making up the lichen's body. These squamules, ranging in colour from yellow to red-brown and typically measuring between 2 and 6 mm in diameter, are notable for their absence of a prothallus#In lichens, prothallus, which is an initial growth phase seen in some lichens. The upper cortex of these lichens is thick and well-developed, while the lower cortex may be poorly developed or entirely absent. Instead of a lower cortex, ''Psora'' species often anchor themselves with a well-developed network of fungal hyphae, which can either lack calcium oxalate crystals and have a brown pigmentation or be colourless, shorter, and densely covered in these crystals.

The symbiotic partner of ''Psora'', the , is , meaning it consists of spherical green algae, forming a continuous layer. The medulla (lichenology), medulla, the innermost layer of the lichen, is well-developed but does not contain iodine-reactive substances (I–).

Reproductive structures, known as apothecia, are (attached directly by their base), and can be found along the margins or on the surface () of the squamules. These structures are typically brown-black, starting flat or slightly convex in their youth, and may become highly convex or semi-spherical as they mature, occasionally with a white or yellow powdery coating (). Unlike some lichens, ''Psora'' does not have a around its apothecia. The , a ring of hyphae surrounding the apothecial , is colourless to pale brown and often becomes obscured as the apothecia mature.

The , the topmost layer inside the apothecia, is red-brown or brown and contains anthraquinones compounds, such as parietin, which react red or purple-red when treated with a potassium hydroxide solution (K+), but do not react with a nitric acid solution (N–). The hymenium, another internal layer, also does not react to iodine (I–). The beneath it is pale brown to colourless and filled with calcium oxalate crystals.

''Psora''s supporting filamentous structures, or paraphyses, are unbranched or sparingly branched and tightly bound together, with slightly swollen tips. The ascus, asci, the spore-bearing cells, are (club-shaped) with eight spores each and have a distinctive blue reaction when stained with iodine, indicative of the ''Porpidia''-type asci without an ocular chamber. Ascospores are colourless, smooth, ellipsoidal, and lack a septum or a thick outer layer (). The genus also produces pycnidia, a type of asexual reproduction, asexual reproductive structure, which are immersed within the squamules and release elongate- (rod-shaped), colourless conidia.

Chemically, ''Psora'' has a range of compounds including depsides, depsidones, anthraquinones, various acids such as pulvinic acid, pulvinic and usnic acids, and triterpenes.

Species

, Species Fungorum (in the Catalogue of Life) accept 16 species of ''Psora''. However, there are additional accepted species that have not yet been added. Although nearly 400 names have been published in this genus, most of these have been reduced to synonymy, transferred to other genera, or are older names that have not been examined with molecular methods.

*''Psora altotibetica''
*''species:Psora brunneocarpa, Psora brunneocarpa''
*''species:Psora crenata, Psora crenata''
*''Psora crystallifera''
*''species:Psora decipiens, Psora decipiens''
*''species:Psora elenkinii, Psora elenkinii'' Rass. (1940)
*''species:Psora globifera, Psora globifera''
*''species:Psora gresinonis, Psora gresinonis'' B. de Lesd. (1930)
*''species:Psora himalayana, Psora himalayana'' (C. Bab.) Timdal (1986)
*''species:Psora hyporubescens, Psora hyporubescens''
*''species:Psora icterica, Psora icterica''
*''species:Psora indigirkae, Psora indigirkae''
*''species:Psora mediterranea, Psora mediterranea'' Evankow & Timdal (2025)
*''species:Psora peninsularis, Psora peninsularis''
*''species:Psora pseudorussellii, Psora pseudorussellii'' Timdal (1986)
*''species:Psora pruinosa, Psora pruinosa''
*''species:Psora rubiformis, Psora rubiformis''
*''species:Psora saviczii, Psora saviczii'' (Tomin) Follmann & A. Crespo (1975)
*''Psora taurensis''
*''species:Psora testacea, Psora testacea''
*''species:Psora vallesiaca, Psora vallesiaca'' (Schaer.) Timdal (1984)

References

{{Taxonbar, from=Q7256114

Lecanorales
Lichen genera
Lecanorales genera
Taxa described in 1796
Taxa named by Georg Franz Hoffmann