Verrucaria nigrescens

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.