Ramalina calicaris is a species of fruticose, bark-dwelling lichen-forming fungus in the family Ramalinaceae. The lichen forms tufted to hanging, greenish-grey shrubby growth anchored by a holdfast at the base, with branches that are often distinctly channelled and strap-shaped, typically 2–3 mm wide and reaching 15–20 cm in length. Its reproductive structures are frequently produced, appearing as pale pink-ochre borne at the tips or margins of the branches, often on bends of angled branches with short spur-like projections. The species grows primarily on the branches and twigs of trees and shrubs with nutrient-rich bark, particularly in coastal settings and humid forests. Chemically, the cortex contains usnic acid, while the medulla may contain compounds of the sekikaic acid complex or lack additional substances.
The species occurs across Europe (where it is most frequent in western districts), North Africa, Macaronesia, and parts of Asia including China, India, and Thailand. The taxonomy of R. calicaris has been complicated by historical confusion over which specimens should be considered the original type material, leading to ongoing nomenclatural debates about the proper application of the name. Linnaeus's original Lichen calicaris encompassed both rock-dwelling and bark-dwelling material, but subsequent lectotypification fixed the name to a rock-dwelling specimen corresponding to Ramalina siliquosa, conflicting with long-established usage for the bark-dwelling species. Several taxa historically described as infraspecific forms of R. calicaris are now recognised as distinct species, including Ramalina farinacea, Ramalina fastigiata, and Ramalina fraxinea. The species is commonly fertile and has been shown (in at least one Asian variety) to be sensitive to nitrogen pollution.
Taxonomy
The name Ramalina calicaris is based on the basionym Lichen calicaris, attributed to Carl Linnaeus in 1753. During this era, the term Lichen was used as a broad generic descriptor for nearly all known lichenized fungi, reflecting an early stage of biological classification where the symbiotic nature of the organism was not yet understood. In the protologue Linnaeus characterized it as an erect, narrow, branching lichen with a pitted (), convex surface and pointed () tips, and gave its habitat as "in Europe, on trees and rocks". The species was reclassified in Ramalina by Johann Christoph Röhling in 1813, a genus erected by Erik Acharius in 1810. Some secondary and regional treatments instead cite the author as Elias Magnus Fries (1824), reflecting a later combination that remains in circulation in parts of the literature and regional databases.
In a 1913 revision of North American Ramalina, Reginald Heber Howe, Jr. reviewed the Linnean Society herbarium sheets associated with Lichen calicaris and reported that, among the specimens he regarded as original material, the better-preserved thalli correspond to the rock-dwelling taxon then treated as Ramalina scopulorum. He therefore argued that Linnaeus's brief was more consistent with that concept than with Fries's later f. canaliculata, illustrating that uncertainty over how the epithet calicaris should be applied predates modern typification and conservation work. In a subsequent instalment of his North American revision, Howe (1914) treated the canaliculate taxon that had often circulated as R. calicaris in older American usage under the name Ramalina canaliculata (Fr.) Herre, tying it to Fries's R. calicaris "canaliculata" concept and summarizing its diagnostic features (including canaliculate laciniae and typically subterminal, spurred apothecia).
Howe also commented on the older "catch-all" use of R. calicaris in North American literature for intergrading forms, and reviewed Vainio's 1888 argument that Linnaeus's epithet calicaris should be applied to Fries's canaliculata on the basis of specimens in the Linnean herbarium. He rejected that evidentiary basis, arguing that the specimens in question were not Linnean types (and were probably added after Linnaeus's death) and that Linnaeus's original description is not diagnostic for the canaliculate taxon.
Sheard and James (1976), in a typification study of the Ramalina siliquosa species aggregate, re-examined the lectotype of Lichen calicaris (LINN 1273.115; lectotype designated by Howe) and reported that it belongs to the R. siliquosa complex and contains protocetraric acid. They also noted that other Linnean material previously treated as "type" for L. calicaris is in poor condition and does not correspond to the corticolous species that most lichenologists had long been calling Ramalina calicaris. A nomenclatural review of Linnaean lichen names reported that Linnaeus's original concept of Lichen calicaris encompassed both saxicolous (rock-dwelling) and corticolous (bark-dwelling) material. It concluded that Howe's lectotypification nevertheless fixes the name to a saxicolous specimen corresponding to Ramalina siliquosa and is "formally correct" under the Code; however, the authors described this outcome as "most unfortunate" because it conflicts with long-established usage of Ramalina calicaris for a corticolous species. To avoid a disruptive name change, the same review indicated that conservation of the name would be proposed so that Lichen calicaris could continue to be used in its traditional sense for the bark-dwelling species. In a separate paper, Jørgensen, James and Jarvis formally proposed conserving Lichen calicaris with a conserved type (from Dillenius's herbarium) that matches the corticolous species, so that Ramalina calicaris would continue in its long-established sense. The Nomenclature Committee for Fungi later recommended acceptance of the Linnaean-name proposals, including conservation of Lichen calicaris, supporting continued use of the name for the bark-dwelling species.
In discussing confusion among fertile, corticolous Ramalina in European herbaria, Groner and LaGreca (1997) traced long-running misapplications to imprecise original and subsequent diagnoses that did not cleanly delimit similar shrubby species, meaning that morphology alone often proved insufficient for routine identification in collections.
Former infraspecific taxa Several taxa historically described as infraspecific types of Ramalina calicaris (forms, varieties, or subspecies) are now recognized as distinct species in Ramalina. These include: Ramalina calicaris f. ecklonii , now Ramalina ecklonii Ramalina calicaris f. farinacea , Ramalina calicaris subsp. farinacea , and Ramalina calicaris var. farinacea , now Ramalina farinacea Ramalina calicaris f. fastigiata and Ramalina calicaris var. fastigiata , now Ramalina fastigiata Ramalina calicaris f. fraxinea , Ramalina calicaris subsp. fraxinea and Ramalina calicaris var. fraxinea , now Ramalina fraxinea Ramalina calicaris f. thrausta , Ramalina calicaris subsp. thrausta , and Ramalina calicaris var. thrausta , now Ramalina thrausta Ramalina calicaris var. dilacerata , now Ramalina dilacerata Ramalina calicaris var. inflata , now Ramalina inflata
Description
Ramalina calicaris is a fruticose (shrubby) lichen with a greenish grey thallus, anchored to the substrate by a basal holdfast. Thalli are often tufted when young, but may become longer and more pendent with age, reaching about 15–20 cm in length in some accounts. The branches (laciniae) are typically strap-shaped and relatively sparingly branched. They are often distinctly channelled (canaliculate) and commonly about 2–3 mm wide, though broader forms have been reported. The surface is described as smooth to weakly wrinkled, and thalli may appear stiff and spiky when dry. Small pores (pseudocyphellae) penetrate the surface; these range from dot-like to spindle-shaped and may be few or numerous depending on the specimen.
Apothecia (spore-producing structures) are usually frequent and in form, typically positioned at or near the tips of the branches, though they can also occur along the margins. They may develop on bends of angled branches and can sometimes show a short spur-like projection. The disc has been described as pale pink-ochre with a thin . The spore-bearing structures (asci) each contain eight spores and have an apical tip whose iodine-staining pattern matches the Bacidia type. Ascospores are hyaline and 1-septate, with reported sizes around 10–16 × 5–7 μm.
The photosynthetic partner () is a green alga. Spot tests on the medulla have been reported as negative (K−, C−, KC−, P−, UV−), with some regional treatments summarizing this as K−/C−. Chemically, the cortex contains usnic acid, while the medulla is variably reported as lacking additional substances or containing compounds of the sekikaic acid complex (including sekikaic and homosekikaic acids). A biochemical study of bark-dwelling lichens on Pyrenean oak (Quercus pyrenaica) in central Spain detected several polyamines—small nitrogen-containing molecules involved in stress responses and growth—in R. calicaris thalli. These compounds (putrescine, spermidine, and spermine) were found both in free form and chemically bound to other cellular components. The same study confirmed the presence of usnic acid and sekikaic acid (the two main secondary metabolites characteristic of this species), and found that usnic acid also occurs in a chemically bound form rather than existing only as free crystals in the lichen tissue.
In some forms the thallus can resemble Evernia prunastri, but R. calicaris has been distinguished by its tough, cartilaginous subcortex and by photobiont cells occurring beneath all thallus surfaces in that comparison. Brandt (1906), in a comparative anatomical study of European Ramalina, described the cortex as a thin layer of cell-like tissue underlain by a near-continuous ring of strengthening hyphae; beneath this lies a loosely woven medulla, with algal cells clustered in a band near the boundary between cortex and medulla. In the same material he reported calcium oxalate in the medulla, no yellow or red colour change of the medulla with potassium hydroxide or barium hydroxide solution ("baryta water"), and no observed breaks of the medulla through the cortex, treating these as anatomical characters useful for comparison among European species.
Similar species
In the field and in herbaria, R. calicaris has often been confused with other fertile, shrubby Ramalina, especially R. fastigiata and R. subgeniculata; Groner and LaGreca (1997) summarized R. calicaris as typically having narrow, canaliculate branches and apothecia that are often subapical to lateral, frequently with an apical "spur", and emphasized secondary chemistry as a practical separator within this complex (for example, evernic acid in R. fastigiata versus divaricatic acid in R. subgeniculata, with R. calicaris reported with sekikaic-acid group substances or sometimes lacking medullary substances).
Wirth (2011) likewise contrasted R. calicaris with R. fastigiata and R. fraxinea, noting differences in growth form and branch morphology, and reported sekikaic acid verified by thin-layer chromatography (TLC) for the 1999 material. Ramalina calicaris can resemble R. elegans, but it differs in having a solid thallus, a more regularly grooved () surface toward the base, and apothecia that are mostly marginal.
Habitat and distribution