''Tholurna'' is a fungal

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

in the family

Caliciaceae The Caliciaceae are a family (taxonomy), family of mostly lichen-forming fungus, fungi belonging to the class (taxonomy), class Lecanoromycetes in the division (mycology), division Ascomycota. Although the family has had its classification chan ...

. The genus is

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

, containing the single species ''Tholurna dissimilis''. Long thought to be confined to

Scandinavia Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...

, it has since been recorded in western North America, where a 1983 survey documented 47 localities from coastal

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

and as far north-east as the

Yukon Yukon () is a Provinces and territories of Canada, territory of Canada, bordering British Columbia to the south, the Northwest Territories to the east, the Beaufort Sea to the north, and the U.S. state of Alaska to the west. It is Canada’s we ...

and

Northwest Territories The Northwest Territories is a federal Provinces and territories of Canada, territory of Canada. At a land area of approximately and a 2021 census population of 41,070, it is the second-largest and the most populous of Provinces and territorie ...

Taxonomy

''Tholurna dissimilis'' was first described by

Johannes Musaeus Norman Johannes Musæus Norman (1823–1903) was a Norwegian botanist, trained as a medical doctor. Norman was the son of a priest, took artium in 1840 and graduated in medicine in 1847. After a short time as a military doctor in the First Schleswig War ...

as ''Podocratera dissimilis'' in 1861; he

circumscribed In geometry, a circumscribed circle for a set of points is a circle passing through each of them. Such a circle is said to ''circumscribe'' the points or a polygon formed from them; such a polygon is said to be ''inscribed'' in the circle. * Circum ...

the new genus ''Tholurna'' the same year to contain the species. Norman's original description characterized ''Tholurna dissimilis'' as a Norwegian

alpine Alpine may refer to any mountainous region. It may also refer to: Places Europe * Alps, a European mountain range ** Alpine states, which overlap with the European range Australia * Alpine, New South Wales, a Northern Village * Alpine National P ...

lichen with a crustose

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

composed of granular- squamules (scales) arranged in a cushion-like formation. He described the podetia (stalked reproductive structures) as simple, parabolic, and corrugated, with a dry,

glaucous ''Glaucous'' (, ) is used to describe the pale grey or bluish-green appearance of the surfaces of some plants, as well as in the names of birds, such as the glaucous gull (''Larus hyperboreus''), glaucous-winged gull (''Larus glaucescens''), ...

or brownish appearance and greenish colouration when moist. The

apothecia An ascocarp, or ascoma (: ascomata), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. As ...

(fruiting bodies) were noted as terminal, solitary, and having an urn-shaped to crater-like form with dark margins that dissolve into a black mass of

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s when moistened. Norman distinguished the genus from related groups like '' Podocratera'' by its characteristic squamulose thallus structure, noting that while Nylander's methodology in his work ''Synopsis'' would place this species within ''Podocratera'', the distinctive thallus warranted recognition of the separate genus ''Tholurna''.

Habitat and distribution

Although the lichen was once considered an alpine specialist, restricted to

krummholz ''Krummholz'' (, "crooked, bent, twisted" and ''Holz'', "wood") — also called ''knieholz'' ("knee timber") — is a type of stunted, deformed vegetation encountered in the subarctic and subalpine tree line landscapes, shaped by continual e ...

and other wind-shorn

conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

tops near the

tree line The tree line is the edge of a habitat at which trees are capable of growing and beyond which they are not. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions (usually low ...

, fieldwork in the 1970s and early 1980s uncovered a far wider ecological range. A compilation of

collections Collection or Collections may refer to: Computing * Collection (abstract data type), the abstract concept of collections in computer science * Collection (linking), the act of linkage editing in computing * Garbage collection (computing), autom ...

revealed populations on numerous mountain summits in the

Coast A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...

and

Cascade Cascade, or Cascading may refer to: Science and technology Science * Air shower (physics), a cascade (particle shower) of subatomic particles and ionized nuclei ** Particle shower, a cascade of secondary particles produced as the result of a high ...

ranges, the

Interior Mountains The Interior Mountains or Northern Interior Mountains are the semi-official names for an expansive collection of mountain ranges that comprises much of the northern half of the Canadian province of British Columbia and a large area of southern Yu ...

, and isolated peaks in the

and

. Occurrences stretch roughly between latitudes 45° N and 62° N, with most sites clustered in moist

montane Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures lapse rate, fall as elevation increases, causing the ecosystem to stratify. This stratification is ...

subalpine zone Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures lapse rate, fall as elevation increases, causing the ecosystem to stratify. This stratification is ...

s west of the

continental divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...

. Two gatherings from

Vancouver Island Vancouver Island is an island in the northeastern Pacific Ocean and part of the Canadian province of British Columbia. The island is in length, in width at its widest point, and in total area, while are of land. The island is the largest ...

provided the first documented insular records for the genus in North America, demonstrating that oceanic influences do not preclude its establishment. The species is

epiphytic An epiphyte is a plant or plant-like organism that grows on the surface of another plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphyt ...

on the exposed branchlets and terminal cones of

spruce A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...

and other

s. While the majority of North-American specimens still come from elevations of , George Otto reported a colony growing at roughly and, most unexpectedly, one thriving just above sea-level in the

Kitimat Kitimat is a district municipality in the North Coast region of British Columbia, Canada. It is a member municipality of the Regional District of Kitimat–Stikine regional government. The Kitimat Valley is part of the most populous urban dist ...

Valley, where an emergent

Sitka spruce ''Picea sitchensis'', the Sitka spruce, is a large, coniferous, evergreen tree growing to just over tall, with a trunk diameter at breast height that can exceed 5 m (16 ft). It is by far the largest species of spruce and the fifth- ...

supported thousands of thalli outside the forest's aerodynamic

boundary layer In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a Boundary (thermodynamic), bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces ...

. These finds indicate that the lichen's key requirement is not altitude per se but an open, wind-swept

microclimate A microclimate (or micro-climate) is a local set of atmosphere of Earth, atmospheric conditions that differ from those in the surrounding areas, often slightly but sometimes substantially. The term may refer to areas as small as a few square m ...

that mimics alpine exposure—conditions met equally on mountain ridges and on tall, isolated trees in humid coastal lowlands.

References

{{Taxonbar, from=Q7786712 Caliciales Caliciales genera Lichen genera Monotypic Lecanoromycetes genera Taxa described in 1861 Taxa named by Johannes M. Norman