Umbilicaria cylindrica, commonly known as the fringed rock tripe, is a leafy lichen found in cold, high-altitude and polar regions across the globe. It forms roughly circular thalli measuring between 2–10 centimetres and is easily recognised with a dark upper surface bordered by a fringe of fine, hair-like projections. As one of the first colonisers of bare rock, it paves the way for more complex communities in areas exposed to intense ultraviolet light. The species is particularly abundant in Arctic–alpine environments, where it can form extensive patches on exposed boulders and rock outcrops. First described scientifically by Carl Linnaeus in 1753, the species has undergone several reclassifications as researchers have explored its varied appearances and chemical traits. While many names have been historically assigned to its various forms, current studies show that these differences are simply variations within one highly variable species. Essential for identification are its maze-like reproductive discs (apothecia) and its distinctive three-layered internal structure. The species exhibits considerable morphological plasticity, with variations in thallus size, colour, and surface texture documented across its range. Beyond its biological appeal,Umbilicaria cylindrica serves an important ecological function. As a pioneer coloniser of rocky surfaces, it contributes to soil formation and creates a microhabitat for specialised fungi and other organisms. Because it absorbs pollutants like heavy metals and radioactive particles directly from the air, this lichen serves as a natural indicator of environmental quality, especially in remote alpine and Arctic areas. Its effectiveness as a biomonitor has made it useful for tracking long-term environmental changes, particularly in regions affected by industrial emissions and nuclear fallout.
Taxonomy The species was first scientifically described by the Swedish taxonomist Carl Linnaeus, who classified it as a member of the eponymous genus Lichen. In his original 1753 diagnosis, Linnaeus characterised the species as a leafy lichen with distinctive ciliate margins and cylindrical, perforated fruiting bodies marked by a "double circle" pattern—referring to the gyrose pattern on the apothecia that remains a key diagnostic feature today. He noted its occurrence in both Pennsylvania and Lapland, demonstrating an early recognition of its broad geographic distribution. These core morphological features that Linnaeus identified—the hairy margins and the distinctive fruiting bodies—continue to be central to the species' identification. The original type specimen, collected in Sweden, is kept in the Linnaean Herbarium in London. In 1830, the French botanist Dominique François Delise reclassified the species into the genus Umbilicaria, establishing the binomial name it is known by today. The species underwent extensive taxonomic revision throughout the nineteenth century, during which European lichenologists proposed numerous transfers between genera and dozens of infraspecific taxa—forms, varieties, and subspecies—based on morphological variations. In his 1950 monograph on Umbilicariaceae in the Western Hemisphere, George Llano noted "The overall characteristics of this very polymorphous species cannot be wholly appreciated on the examination of a few specimens. He then provided a key to varieties and forms of U. cylindrica, which contained 13 entries, and further noted that this list did not cover the entirety of variation documented in this species. While these historical names remain in the nomenclatural record, none are now considered taxonomically distinct from the typical form. These include var. fimbriata (characterised by abundant dark bristles spread in all directions) and var. denticulata (with thallus-coloured bristles lying in the same plane). The taxonomic placement and classification of U. cylindrica has undergone several revisions over time. In their 1993 monograph on Asian Umbilicariaceae, Jian-chun Wei and Yu-mei Jiang re-evaluated previous taxonomic misapplications of Umbilicaria cylindrica and introduced the epithet U. neocylindrica for specimens that had been erroneously referred to as U. cylindrica in some sources. They observed that this misapplication primarily affected Asian collections and that U. neocylindrica was morphologically similar to U. umbilicarioides. However, U. cylindrica itself can be distinguished from U. umbilicarioides by the absence of thalloconidia and the presence of conspicuous papillae on its lower surface. While U. neocylindrica was proposed to clarify nomenclatural inconsistencies, it has not been widely adopted in global taxonomic frameworks and is not recognised as a distinct species in recent phylogenetic analyses of Umbilicaria. The species shows significant morphological, chemical, and genetic variation throughout its circumpolar range. Studies have shown considerable enzyme polymorphism and morphological differences between populations, demonstrating the species' adaptability across its distribution. Studies have documented up to six varieties from the Iberian Peninsula and five from the Tatra Mountains in Poland, distinguished by features such as rhizine density, surface texture, and thallus colouration. The phylogenetic relationships of U. cylindrica were clarified in a 2017 molecular study by Davydov and colleagues. Their analysis placed U. cylindrica within "Clade 3" (subgenus Umbilicaria), where it forms part of the U. cylindrica group alongside several close relatives including U. altaiensis, U. dendrophora, U. maculata, and U. umbilicarioides. This group is characterised by having an elevated pruinose or reticulate-ridged centre on the upper surface of the thallus. Studies have revealed variations among specimens in chemical composition, particularly in the quantities of gyrophoric and lecanoric acids, as well as differences in morphological and physiological characteristics. The species within this group are typically distributed in high mountainous and subpolar regions, occurring either throughout both hemispheres or restricted to the Holarctic region. Umbilicaria cylindrica is commonly known as the "fringed rock tripe" in North America.
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