Verrucaria nigrescens
From Wikipedia, the free encyclopedia
| Verrucaria nigrescens | |
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Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Eurotiomycetes |
| Order: | Verrucariales |
| Family: | Verrucariaceae |
| Genus: | Verrucaria |
| Species: | V. nigrescens |
| Binomial name | |
| Verrucaria nigrescens Pers. (1795) | |
| Synonyms[2] | |
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List
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Verrucaria nigrescens is a widespread species of crustose lichen in the family Verrucariaceae. First described by Christiaan Hendrik Persoon in 1795, it has maintained its original name despite accumulating many synonyms over its complex taxonomic history. The species is characterised by its dark-brown, areolate (cracked into small polygonal segments) thallus, and commonly colonises stone surfaces, especially limestone. Due to its dark pigmentation, V. nigrescens significantly absorbs sunlight, elevating temperatures on the rock surfaces it inhabits. This contributes to stone deterioration, posing challenges for conservation of historical monuments and buildings, and has prompted research into specialised control methods such as laser cleaning.
It was first formally described as a new species by Christiaan Hendrik Persoon in 1795.[3] Despite a long and varied taxonomic history during which numerous synonyms have accumulated, the species retains its original name.[2]
Description
Verrucaria nigrescens is a crustose lichen that forms a superficial, dark brown layer varying in thickness from thin to thick (100–500 μm). The thallus (main body) is characteristically divided into small polygonal sections called areoles, which measure 200–800 μm in diameter. These areoles typically have smooth surfaces that range from flat to slightly convex, with occasional blastidiate (bud-like) margins. The sides of these areoles appear brown to blackish in colour.[4]
The lichen generally lacks a prothallus (an initial growth stage visible at the edges), or if present, it is inconspicuous or slightly darker than the main thallus, sometimes visible in the spaces between areoles. Internally, the lichen has a thin upper cortex (protective outer layer) measuring 10–20 μm thick, with a brownish uppermost portion. Beneath this lies the algal layer (30–120 μm thick), where the photosynthetic cells are arranged in approximately vertical columns. The medulla (inner layer) features a distinctive black basal layer comprising half to two-thirds of the thallus thickness.[4]
The reproductive structures, called perithecia, are partially immersed in the thallus (half to three-quarters embedded), with typically one perithecium per areole. The apex (top) of each perithecium ranges from flat to hemispherical in shape. The involucrellum (a protective covering around the perithecium) measures 200–400 μm in diameter and can be hemispherical or extend to the base level of the perithecium. In cross-section, perithecia measure 150–250 μm in diameter, with a dark brown exciple (inner wall of the fruiting body).[4]
The ascospores (spores produced in specialised cells called asci) are ellipsoidal in shape, typically measuring 19–27 by 8–14 μm. Conidiomata (asexual reproductive structures) have not been observed in this species.[4][5]
Habitat and distribution
Ecological interactions
Verrucaria nigrescens is among several calcicolous lichen species grazed by terrestrial snails. Laboratory studies have shown that three snail species—Balea perversa, Helicigona lapicida, and Clausilia bidentata—intensively graze on V. nigrescens, whereas the snail species Chondrina clienta tends to avoid it. The selective grazing is likely influenced by physical characteristics of the lichen, such as the carbonised tissues, since V. nigrescens does not produce chemical defence metabolites common in other lichens. Snail herbivory has implications for the survival and colonisation strategies of lichens, potentially affecting their population dynamics and ecological interactions on calcareous substrates.[7]
Several species of lichenicolous (lichen-dwelling) fungi have been recorded inhabiting Verrucaria nigrescens populations in Ukraine. These include Endococcus rugulosus, Muellerella lichenicola, Opegrapha opaca, Polycoccum marmoratum, Zwackhiomyces calcisedus, and Zwackhiomyces lithoiceae.[8]
