Hypogymnia Dichroma

''Hypogymnia'' is a genus of foliose lichens in the family Parmeliaceae. They are commonly known as tube lichens, bone lichens, or pillow lichens. Most species lack rhizines (root-like attachment organs on the lower surface) that are otherwise common in members of the Parmeliaceae, and have swollen lobes that are usually hollow. Other common characteristics are relatively small spores and the presence of physodic acid and related lichen products. The lichens usually grow on the bark and wood of coniferous trees.

''Hypogymnia'' was proposed by lichenologist William Nylander, first as a subgenus of '' Parmelia'' in 1881, and 15 years later as a distinct genus of two species, including the widespread and common type species, ''Hypogymnia physodes''. It has since grown to about 90 recognized species. ''Hypogymnia'' has a centre of biodiversity in China, where many of its species are found.

Taxonomy

''Hypogymnia'' was first created as subgenus of '' Parmelia'' by Finnish lichenologist William Nylander in 1881. He associated it with the species ''Parmelia physodem'' (which ultimately became the type species, ''Hypogymnia physodes''), noting the lack of rhizines as the characteristic distinguishing it from ''Parmelia''. Nylander later promoted it to generic status in 1896. At this time, the genus contained only two species: ''Hypogymnia pertusa'' (currently named ''Menegazzia terebrata'') as well as the type species. For many decades afterwards, the genus did not have widespread recognition, as most lichenologists preferred to include the "hypogymnioid" lichens in the classic form genus ''Parmelia''. In 1951 Hildur Krog considered the morphology and chemistry of this group of species to be distinctive and reinstated the genus ''Hypogymnia''. Krog included four subgenera, including ''H''. subg. ''Cavernularia'' and ''H''. subg.''Everniiformes''. These later became accepted as distinct genera (the former only temporarily; see synonymy below), the latter under the name ''Pseudevernia''.

In 1974, Krog published an account of three Northern Hemisphere ''Hypogymnia'' species that grow on acid rock in arctic and alpine habitats. These species, namely ''H.  atrofusca'', ''H. intestiniformis'', and ''H. oroarctica'', make up the ''H. intestiniformis'' group. This biologically discontinuous assemblage of species was segregated from ''Hypogymnia'' by Trevor Goward under the genus name ''Brodoa'' in 1986. It differs from ''Hypogymnia'' in its compact medulla, larger spores and different cortical structure.

''Hypogymnia'' is classified in the Parmeliaceae. The family Hypogymniaceae has been proposed in the past to contain the genus and other similar hypogymnioid lichens, but this taxonomic arrangement has not been widely accepted by other taxonomists. For example, Krog argued that no critical characters had been suggested that could be used as a defining familial characteristic. In the Parmeliaceae, ''Hypogymnia'' belongs to the hypogymnioid clade along with the genera ''Arctoparmelia'', ''Brodoa'', and ''Pseudevernia''. All of these genera share the common characteristic of having a loosely compact medulla.

''Hypogymnia'' lichens are commonly known as "tube lichens", "bone lichens", or "pillow lichens". The name ''Hypogymnia'', derived from the Ancient Greek - (''hupó'', meaning "under") and (''gumnós'', meaning "naked"), refers to the bare lower surface of the thallus.

Synonymy

Synonyms of ''Hypogymnia'' are ''Cavernularia'', created by Gunnar Degelius in 1937, and ''Ceratophyllum'', created by Maurice Choisy in 1951. ''Cavernularia'' contained two hypogymnoid species, ''C. lophyrea'' and ''C. hultenii''. This species pair has an array of pronounced but small depressions in the lower surface, instead of the smooth or irregularly wrinkled surface typical of ''Hypogymnia''; Degelius called these minute cavities (about 0.1 mm diameter) "cavernulae". The two ''Cavernularia'' species are otherwise similar to ''Hypogymnia'' in terms of overall morphology, microstructure of the apothecia, and chemistry. Molecular analysis showed that ''Cavernularia'' needed to be subsumed into ''Hypogymnia'' in order for the latter genus to be monophyletic. This suggested synonymy had already been proposed several decades earlier by Veli Räsänen in 1943 and Hildur Krog in 1952, but not adopted by later authors, including Krog herself.

Description

''Hypogymnia'' is a genus of medium to large foliose lichens. They are typically greenish grey to brownish grey in colour; some species are yellowish (from usnic acid). The thallus comprises more or less inflated but hollow (tube-like) lobes. These lobes often have a perforation at the tip. The colour of the ceiling of the tubes (the medullary surface) is dark brown or white, and is often used as a characteristic to distinguish between species. The lower surface of the tube is black with a smooth or wrinkled texture.

Rhizines are root-like attachment organs on the lower surface of a lichen thallus, made of elongated strands of hyphae; a shorter version of this attachment organ is called a ''hapter''. Although many recent lichen floras and manuals describe ''Hypogymnia'' as lacking rhizines, a 2015 study challenges the universality of this assertion. In the study, researchers studied a large number of ''Hypogymnia'' collections, representing 72 species as well as 64 type specimens. They found that rhizines and hapters were occasionally present on the lower surface of 35 species. Two types of attachment organs are found: slender rhizines with fine and tapering tips (found in ''H. krogiae'' and ''H. subfarinacea''), and the more common hapters, which are thick with broken tips. Both types are dark brown to black and usually the same colour as the lower surface. In all cases where these attachment organs are found, however, they are few in number and are sparsely distributed on the lower thallus surface.

The apothecia of ''Hypogymnia'' are lecanorine in form with a constricted base and are often raised or shaped like an urn. The apothecial discs are red-brown and typically concave. Ascospores are colourless, ellipsoid, and number eight per ascus. They are relatively small, less than 9 μm long. Pycnidia are black and appear as small dots on the surface of the lobes. The photobiont from the genus ''Trebouxia''.

The cortex contains atranorin (responsible for the grey colour), while the medullae of most species have physodic acid, and some species contain other orcinol and beta-orcinol depsidones, including protocetraric acid and physodalic acid.

The genus ''Menegazzia'' contains species that could be confused with ''Hypogymnia''; ''Menegazzia'', however, has perforations on the upper lobe surface, unlike ''Hypogymnia''. Other superficially similar genera, such as ''Brodoa'' and '' Allantoparmelia'', can be distinguished from ''Hypogymnia'' by their solid lobes.

Habitat and distribution

''Hypogymnia'' species usually grow on bark and wood, particular that of conifers. Less frequently, they are found on rock or mossy soil. The genus has been recorded on all continents except Antarctica. In tropical to subtropical locations, ''Hypogymnia'' appears to be restricted to high elevations, where temperatures are cooler. Seventeen species are recorded from the Himalayan region of India and Nepal, while 31 species are present in North America. In Mexico, it is relatively rare; of the 11 species recorded from there, only two are known from more than 10 collections, and only one, '' H. guadalupensis'', is endemic to the country. Nine species occur in Europe. Southwestern China is a centre of biodiversity for the genus, as more than 40 species occur there. It is one of the few large Parmeliaceae genera that has its main distribution in the Northern Hemisphere.

Ecology

There are several lichenicolous fungi that are known to infect ''Hypogymnia'' species. Some of them parasitise specific lichens, such as '' Plectocarpon hypogymniae'' (on ''Hypogymnia bitteri''), '' Lichenopeltella hypogymniae'' (on ''Hypogymnia zeylanica''), '' Muellerella antarctica'' (on ''Hypogymnia antarctica''), '' Phacopsis cephalodioides'' (on ''Hypogymnia physodes''). Others have a less specific host range, including '' Abrothallus prodiens'', '' Epithamnolia xanthoriae'', '' Minutoexcipula calatayudii'', '' Trichonectria anisospora'', '' Endophragmiella franconica'', '' Cyphobasidium hypogymniicola'', '' Tremella hypogymniae'', and ''Tremella papuana''. The thalli of ''Hypogymnia physodes'' are inhabited by various species of orbatid mites.

Uses

''Hypogymnia physodes'' has been used as a biomonitor for several applications. Examples include monitoring atmospheric nitrogen and sulphur deposition in Norway, the accumulation of mercury downwind of chloralkali plant in Wisconsin, and pollution from several toxic heavy metal elements following the closure of a large mine waste dump close to Zlatna, Romania. It was also used to help evaluate the levels of radionuclides deposited in the environment after the East Urals (1957) and Chernobyl (1988) nuclear accidents. ''H. tubulosa'' is an indicator species of old-growth forests. In China, ''H. physodes'' and ''H. pseudoenteromorpha'' are used as raw materials in the preparation of litmus reagent.

In 15th-century Europe, ''Hypogymnia physodes'' was one component (in addition to '' Evernia prunastri'' and ''Pseudevernia furfuracea'') of the popular drug "Lichen quercinus virdes". In Traditional Chinese Medicine, ''Hypogymnia hypotrypa'' is used for "dim vision, bleeding from uterus, bleeding from external injury, chronic dermatitis, and sores." ''Hypogymnia flavida'' and ''H. hypotrypa'' serve as raw material in the preparation of antibiotics in China.

Species

About 90 species are recognized in the genus.









*'' Hypogymnia alpina'' – China; India; Nepal
*''Hypogymnia amplexa''
*''Hypogymnia arcuata'' – widespread in Northern Hemisphere
*'' Hypogymnia asahinae'' – Japan
*'' Hypogymnia austerodes'' – Europe
*'' Hypogymnia australica''
*'' Hypogymnia beringiana'' – Alaska; Russia
*'' Hypogymnia billardierei''
*'' Hypogymnia bitteri'' – Asia; Europe
*'' Hypogymnia bryophila'' – Portugal
*'' Hypogymnia bulbosa'' – China; Taiwan
*'' Hypogymnia canadensis'' – North America
*'' Hypogymnia capitata'' – China
*'' Hypogymnia castanea'' – Alaska; Far East Russia
*'' Hypogymnia congesta'' – China
*'' Hypogymnia crystallina'' – Himalayas
*'' Hypogymnia delavayi'' – China
*'' Hypogymnia dichroma'' – American Cordillera
*'' Hypogymnia diffractaica'' – China
*'' Hypogymnia discopruina'' – southwestern China
*'' Hypogymnia duplicata''
*'' Hypogymnia elgonensis'' – Africa
*''Hypogymnia elongata''
*'' Hypogymnia enteromorphoides''
*'' Hypogymnia farinacea'' – Europe
*'' Hypogymnia fistulosa'' – Aleutian Islands; other islands in the Bering Sea; Seward Peninsula
*'' Hypogymnia flavida'' – East Asia
*'' Hypogymnia fragillima'' – northeast Asia
*'' Hypogymnia fujisanensis''
*'' Hypogymnia gracilis''
*'' Hypogymnia guadalupensis''
*'' Hypogymnia hengduanensis'' – Asia
*'' Hypogymnia heterophylla'' – North America
*'' Hypogymnia hokkaidensis'' – Japan
*'' Hypogymnia hultenii''
*'' Hypogymnia hypotrypa'' – Asia
*'' Hypogymnia imshaugii'' – Alaska
*'' Hypogymnia inactiva''
*'' Hypogymnia incurvoides'' – Europe
*''Hypogymnia inflata'' – Africa
*''Hypogymnia irregularis'' – Asia
*'' Hypogymnia kangdingensis''
*'' Hypogymnia kiboensis'' – Africa
*'' Hypogymnia kosciuskoensis'' – Australia
*'' Hypogymnia krogiae'' – North America
*'' Hypogymnia laccata'' – southwest China
*''Hypogymnia laminisorediata'' – Greece; Morocco
*'' Hypogymnia laxa'' – China
*'' Hypogymnia lijiangensis'' – China
*'' Hypogymnia lugubris''
*'' Hypogymnia lophyrea''
*'' Hypogymnia macrospora'' – China
*'' Hypogymnia madeirensis''
*'' Hypogymnia magnifica'' – China
*'' Hypogymnia metaphysodes'' – Asia
*'' Hypogymnia minilobata'' – United States
*'' Hypogymnia mollis'' – North America
*'' Hypogymnia mundata''
*'' Hypogymnia nikkoensis''
*'' Hypogymnia nitida'' – China
*'' Hypogymnia obscurata''
*'' Hypogymnia occidentalis'' – Oregon
*'' Hypogymnia oceanica'' – North America
*'' Hypogymnia papilliformis'' – Russian Far East; China
*'' Hypogymnia pectinatula'' – Java; Papua New Guinea; Philippines; North Borneo
*'' Hypogymnia pendula'' – China
*''Hypogymnia physodes'' – widespread in Northern Hemisphere
*'' Hypogymnia protea'' – American Cordillera
*'' Hypogymnia pruinoidea'' – China
*'' Hypogymnia pruinosa'' – China
*'' Hypogymnia pseudobitteriana'' – Asia; Papua New Guinea
*'' Hypogymnia pseudocyphellata'' – China
*'' Hypogymnia pseudoenteromorpha'' – Japan
*'' Hypogymnia pseudophysodes'' – northeast Asia
*'' Hypogymnia pseudopruinosa'' – China
*'' Hypogymnia pulchrilobata''
*'' Hypogymnia pulverata''
*'' Hypogymnia recurva'' – North America
*'' Hypogymnia rhodesiana'' – Africa
*'' Hypogymnia sachalinensis'' – east Asia
*'' Hypogymnia salsa'' – American Cordillera
*''Hypogymnia saxicola'' – China
*'' Hypogymnia schizidiata''
*'' Hypogymnia sikkimensis'' – Sikkim, India
*'' Hypogymnia sinica'' – China
*'' Hypogymnia stricta'' – Asia
*'' Hypogymnia subarticulata'' – Asia
*'' Hypogymnia subcrustacea''
*'' Hypogymnia subduplicata''
*'' Hypogymnia subfarinacea'' – China
*'' Hypogymnia submundata''
*'' Hypogymnia subobscura'' – Europe
*'' Hypogymnia subphysodes''
*'' Hypogymnia subpruinosa'' – China
*'' Hypogymnia subvittata''
*'' Hypogymnia taiwanalpina'' – Taiwan
*'' Hypogymnia tasmanica''
*'' Hypogymnia tavaresii'' – Canary Islands
*'' Hypogymnia tenuispora'' – China
*'' Hypogymnia thomsoniana'' – Asia
*'' Hypogymnia tubularis''
*'' Hypogymnia tubulosa'' – Europe
*'' Hypogymnia tuckerae'' – Oregon & California
*'' Hypogymnia turgidula''
*'' Hypogymnia verruculosa'' – American Cordillera
*'' Hypogymnia vittata'' – Asia; Europe; North America
*''Hypogymnia wattiana''
*'' Hypogymnia wilfiana'' – North America
*'' Hypogymnia yunnanensis'' – China
*'' Hypogymnia zeylanica'' – Sri Lanka

Hypogymnia contains three species pairs: ''H. krogiae'' and the sorediate counterpart ''H. incurvoides'', ''H. minilobata'' and the sorediate ''H. mollis'', and ''H. lophyrea'' and the sorediate ''H. hultenii''.

References

Cited literature

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Lichen genera
Lecanorales genera
Taxa described in 1881
Taxa named by William Nylander (botanist)