Thelocarpon is a genus of lichen-forming fungi in the family Thelocarpaceae.[1] The genus was established in 1853 by the Finnish lichenologist William Nylander, who distinguished it from related genera by its warted thallus structure, many-spored asci, and the distinctive violet-blue staining reaction of its fruiting body gel when treated with iodine. These tiny lichens form small, wart-like bumps on soil, wood, and plant debris, often covered with a distinctive bright yellow powdery coating. The genus includes about 30 species found worldwide, many of which produce unusually large numbers of ascospores—sometimes over 300 per spore sac.
The genus was circumscribed in 1853 by the Finnish lichenologist William Nylander. He established the genus to accommodate lichens with a whitish thallus composed of granular , clustered wart-like structures that sit above papillae and are perforated by mostly subtle pores, each containing a single pale, somewhat enlarged apothecium (fruiting body). He characterised the genus by its cylindrical-spindle-shaped, many-spored asci containing 24–80 or more ascospores per ascus, with the spores being pale yellow, ellipsoid, frequently single-celled. Nylander noted the presence of slender, very abundant paraphyses and observed that the genus was related to Endocarpon, commenting that it belonged to the tribe Endocarpeae. He distinguished Thelocarpon from the previously described Sphaeropsis by its different thallus characteristics, proposing the new genus name after noting that the mucilaginous hymenium was stained violet-blue by iodine and potassium iodide.[2]
Description
Thelocarpon species are minute lichens whose thallus, when present, wraps around the developing fruit-body so that the two form a tiny, wart-like mound. In many species this sheath is so reduced that the ascoma appears to sit naked on the substrate; a few taxa instead develop a thin, scaly crust. The photosynthetic partner, when there is one, is a single-celled green alga, but some species lack algae altogether and rely on absorbed nutrients.[3]
The sexual fruit-bodies occur in two basic forms. Most species produce perithecia: minute, globose or flask-shaped flasks that open through a pore, while others form apothecia that resemble short cylinders or low discs with the spore layer exposed. Either type may sit on the surface or be slightly sunk into it, and the exterior is often dusted with a bright yellow powdery coating ( pruina ) produced by pulvinic acid pigments. The outer wall ( exciple ) is pale or colourless and contains no dark melanins. Inside, the hamathecium consists of a mesh of delicate, branching filaments—paraphyses, periphysoids and periphyses —that are embedded in a jelly. This jelly is diagnostic: it stays clear in iodine solution or, at higher iodine strength, turns red and then deep blue after potassium iodide pretreatment, a reaction called hemiamyloidy. The asci are bottle- to tube-shaped, sometimes with a slightly thickened tip ( tholus ), and each sac bursts to release a crowd of ascospores—anywhere from a dozen to more than 300. The spores are tiny, colourless, mostly one-celled and usually contain a pair of oil droplets.[3]
Asexual reproduction takes place in equally small pycnidia, flask-like structures that share the same wart-like cover as the perithecia. These generate cylindrical or short-ellipsoidconidia that are usually single-celled but may occasionally show up to two cross-walls. Many Thelocarpon species manufacture pulvinic acid derivatives such as vulpinic acid and pulvinic dilactone; when these pigments are secreted to the surface they create the conspicuous yellow pruina, but in some taxa they are locked within the upper exciple instead. The combination of multispored asci, vivid yellow chemistry and the warted habit makes the genus distinctive among crustose lichens found on nutrient-poor soils, wood and decaying plant debris.[3]
↑ Groenhart, P. (1954). "Malaysian lichens–IV". Reinwardtia. 2 (3): 385–402.
↑ Flakus, Adam; Kukwa, Martin (2014). "The first squamulose Thelocarpon species (Thelocarpaceae, Ascomycota) discovered in the biological soil crusts in the Bolivian Andes". Phytotaxa. 175 (5): 281. doi:10.11646/phytotaxa.175.5.7.
↑ Lettau, G. (1955). "Flechten aus Mitteleuropa X" [Lichens of Middle Europe X]. Feddes Repertorium Specierum Novarum Regni Vegetabilis (in German). 57: 1–94 [75].
↑ Nylander, W. (1867). "Addenda nova ad lichenographiam Europaeam. Cont. IV" [New additions to European lichenography. Continuation IV]. Flora (in Latin). 50: 177–180.
↑ Nylander, W. (1855). "Essai d'une nouvelle classification des lichens, (second mémoire)" [Essay on a new classification of lichens, (second memoir)]. Mémoires de la Société Impériale des Sciences Naturelles de Cherbourg (in Latin). 3: 161–202 [191].
1 2 Salisbury, G. (1953). "The genus Thelocarpon in Britain". North Western Naturalist. 1953: 66–76.
↑ Van den Boom, P.P.G. (2016). "Lichens and lichenicolous fungi of the Azores (Portugal), collected on São Miguel and Terceira with the descriptions of seven new species". Acta Botanica Hungarica. 58 (1–2): 199–222 [213]. doi:10.1556/034.58.2016.1-2.11.
↑ Moon, K.H.; Aptroot, A. (2009). "Pyrenocarpous lichens in Korea". Bibliotheca Lichenologica. 99: 297–314.
↑ Bouly de Lesdain, Maurice (1914). Recherches sur les lichens des environs de Dunkerque, 1er supplément[Research on the lichens of the surroundings of Dunkirk, 1st supplement] (in French). Société dunkerquoise pour l'encouragement des sciences, des lettres et des arts. p.149.
↑ David, J.C.; Coppins, B.J. (1997). "Thelocarpon opertum (Acarosporaceae), a new species from the British Isles". The Lichenologist. 29 (3): 291–295. doi:10.1006/lich.1996.0070.
↑ Awasthi, D.D.; Singh, K.P. (1975). "Three new taxa of lichens from Palni Hills, India". Geophytology. 5 (1): 39–42.
↑ Eitner, E. (1901). "Zweiter Nachtrag zur schlesischen Flechtenflora" [Second supplement to the Silesian lichen flora]. Jahresbericht der Schlesischen Gesellschaft für Vaterländische Kultur (in German). 78: 5–27 [13].
↑ Magnusson, A.H. (1955). "A catalogue of the Hawaiian Lichens". Arkiv för Botanik. 2. 3 (10): 223–402.
↑ Zahlbruckner, A. (1902). "Beiträge zur Flechtenflora Niederösterreichs. VI" [Contributions to the lichen flora of Lower Austria. VI]. Verhandlungen der Zoologisch-Botanischen Gesellschaft in Wien (in German). 52: 257–270.
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