Lobothallia

''Lobothallia'' is a genus of lichen-forming fungi in the family Megasporaceae. Dark brown to black apothecia may be sunken into the surface of the thallus, as indicated in the common name puffed sunken-disk lichen. Originally described as a subgenus of ''Aspicilia'' in 1984, ''Lobothallia'' was elevated to full genus status in 1991 based on distinctive features including peripheral and small, thin-walled ascospores. The genus was established to clarify a group of rock-dwelling lichens that had previously been classified across several different genera.

The genus is found across multiple continents including Eurasia, North America, and Australia, with the greatest diversity occurring in the semi-arid mountains of Central Asia. These lichens typically grow on exposed rock faces, from low-elevation steppes to high mountain areas above 2,600 meters, and are well-adapted to dry conditions. As of 2025, the genus includes 28 recognized species, with several new species recently discovered in Pakistan and China.

Taxonomy

''Lobothallia'' was first proposed as a subgenus of the genus ''Aspicilia'' by Georges Clauzade and Claude Roux in 1984. They circumscribed the taxon as a morphologically coherent group of saxicolous (rock-dwelling) crustose lichens whose thallus forms conspicuous peripheral while the central portion breaks into cracked or low‑ that lack . In section, the apothecial gives a negative or only very faint positive reaction in the nitrite (N) spot‑test, and the hymenium is composed of predominantly (unbranched) paraphyses. The authors further separated the group from other ''Aspicilia'' lineages by the possession of small, thin‑walled, non‑ ascospores measuring 10–15 × 6–8 μm, in contrast to the very large thick‑walled spores of their subgenus '' Megaspora'' and the papillose, chalky thallus with branched paraphyses that define ''Pachyothallia''.

They selected ''Aspicilia alphoplaca'' as the type species of ''Lobothallia'' and, in the same paper, assigned ''A. melanaspis'', ''A. praeradiosa'' and ''A. subcircinata''—together with several names then treated under '' Circinaria'' and ''Lecanora''—to the new subgenus. By doing so, Clauzade and Roux effectively clarified a suite of taxa that had long been shuffled between disparate genera, offering a diagnosis based on thallus architecture and ascus anatomy rather than on chemical or ecological convenience. Josef Hafellner elevated ''Lobothallia'' to distinct genus status in 1991 as part of a reorganization of ''Aspicilia'' and related genera.

Description

The thallus of ''Lobothallia'' ranges from a tight crust that clings to the rock to a more leaf-like, lobed rosette. It is built from angular, tile-like patches () that radiate outward; the outermost ones spread into plate-shaped , a form called ; thalli grow to . Unlike many foliose lichens, the underside lacks distinct rhizines (the root-like anchoring strands). The partner is green alga from the genus ''Trebouxia''.

Fruiting bodies (apothecia) appear early as small, cup-shaped pits sunk in the thallus. With age they rise to sit on the surface, flatten, and occasionally develop a short stalk. Each apothecium is ringed by a thick collar of thallus tissue (the ) that may become wavy, while the exposed turns reddish-brown to black and can warp in mature specimens. Microscopy reveals an olive- to red-brown that either shows no reaction or a faint green tint to the standard nitrate test (N–/N+). The supporting paraphyses are mostly unbranched but swell into bead-like tips. Inside ''Aspicilia''-type asci sit eight broadly ellipsoidal, thin-walled ascospores—small for the Megasporaceae—and the lichen also produces minute ellipsoidal to rod-shaped conidia for asexual dispersal.

Habitat and distribution

The widely distributed genus is represented in Eurasia, North Africa, Central America, western North America, and Australia. Species of ''Lobothallia'' are overwhelmingly saxicolous, occupying exposed faces of siliceous or calcareous bedrock ranging from low‑elevation steppe outcrops (roughly 200 m elevation) to high‑montane belts above 2,600 m. The genus is characteristically northern‑hemispheric, with its greatest diversity recorded in the semi‑arid mountains of Central Asia—especially the Altai system where 12 taxa occur—and in the Mediterranean–Alpine arc; by contrast, only five species reach Fennoscandia and the Urals, and very few extend into boreal substrates beyond 50° N.

Substratum specificity is broad in ''Lobothallia'': some taxa favour basic limestones, others siliceous schists, gneiss or serpentinite, and several tolerate heavily weathered desert sandstones. Thalli are highly adapted to xeric microclimates—lobes in many species are thick, and tightly , reducing water loss under intense insolation—yet a few in the genus exploit very different niches. The freshwater specialist ''L. hydrocharis'' forms extensive placodioid crusts in the splash zone of shaded mountain streams on Sardinia, where it structures a distinctive rheophytic lichen community rich in parasitic and epilichenic interactions; true submersion is avoided, but thalli are periodically inundated by water. At the opposite moisture extreme, several Asian members (e.g. ''L. brachyloba'' and ''L. zogtii'') inhabit fully insolated desert pavements where summer surface temperatures exceed . Ecological plasticity also includes a transient lichenicolous (lichen-dwelling) phase: ''L. epiadelpha'' initiates development on the thalli of ''Circinaria maculata'' before overgrowing the host and becoming free‑living, while certain chemotypes of ''L. radiosa'' begin as facultative parasites on ''Aspicilia'' (in the loose sense)

Recent discoveries have broadened the known range of the genus into the Himalayas and Hindu Kush. Four species new to science—''L. elobulata'', ''L. iqbalii'', ''L. pakistanica'' and ''L. pulvinata''—were collected on crystalline blocks and thin soil veneers between in northern Pakistan, demonstrating that continental Asian lineages extend well into subtropical montane belts. In the neighbouring Margalla Hills, ''L. densipruinosa'' colonises sun‑facing conglomerate ledges at roughly 900 m elevation, its dark‑olive discs protected by a dense cortical pruina. China has yielded parallel novelties—''L. crenulata'', ''L. lobulata'' and ''L. subdiffracta'' var. ''rimosa''—which, together with previously known taxa, form a well‑supported eastern Asian clade growing on granitic ridges between 1,500 m and 2,400 m.

Species

, Species Fungorum accepts 28 species of ''Lobothallia''.
* '' Lobothallia alphoplaca''
* '' Lobothallia brachyloba''
* '' Lobothallia chadefaudiana''
* '' Lobothallia cheresina''
* '' Lobothallia controversa''
* '' Lobothallia crassimarginata'' – China
* '' Lobothallia crenulata'' – China
* '' Lobothallia densipruinosa''
* '' Lobothallia determinata''
* '' Lobothallia elobulata'' – Pakistan
* '' Lobothallia epiadelpha''
* '' Lobothallia farinosa''
* '' Lobothallia gangwondoana''
* '' Lobothallia hedinii''
* '' Lobothallia helanensis'' – China
* '' Lobothallia hydrocharis''
* '' Lobothallia iqbalii'' – Pakistan
* '' Lobothallia kuminovae''
* '' Lobothallia lacteola''
* '' Lobothallia lobulata'' – China
* '' Lobothallia melanaspis''
* '' Lobothallia pakistanica'' – Pakistan
* '' Lobothallia peltastictoides''
* '' Lobothallia platycarpa''
* '' Lobothallia praeradiosa''
* '' Lobothallia pruinosa'' – China
* '' Lobothallia pulvinata'' – Pakistan
* '' Lobothallia radiosa''
* '' Lobothallia recedens''
* '' Lobothallia semisterilis''
* '' Lobothallia subdiffracta''
* '' Lobothallia uxoris''
* '' Lobothallia zogtii''

References

{{Taxonbar, from=Q10568648

Megasporaceae
Pertusariales genera
Lichen genera
Taxa described in 1984
Taxa named by Georges Clauzade
Taxa named by Claude Roux