Peltidea

''Peltigera'' is a genus of approximately 100 species of foliose lichens in the family Peltigeraceae. Commonly known as the dog or pelt lichens, species of ''Peltigera'' are often terricolous (growing on soil), but can also occur on moss, trees, rocks, and many other in many parts of the world.

Most species of ''Peltigera'' have the cyanobacterium ''Nostoc'' as the dominant photobiont but some have the algae ''Coccomyxa.'' The presence of both a green alga and a cyanobacterium makes some tripartite; in this case they show cephalodium growths containing the third partner, ''Nostoc''. Because of their ability to fix nitrogen from the atmosphere, such lichens are influential in soil composition and generation.

Description

Species of ''Peltigera'' are foliose, with broad lobed thalli. Although the size of the thalli is variable and species-dependent, in some species the thalli can grow quite large, up to 30 cm in diameter.Vitikainen O. (1994). (1998). Taxonomic notes on neotropical species of ''Pelitgera''. In: Lichenology in Latin America: history, current knowledge and applications. Edited by M. P. Marcelli, and M.R.D. Seaward. CETESB, Companhia de Tecnologia de Saneamento Ambiental, Estado de Sao Paulo. pp. 135-139. The color of the upper surface may range from drab gray, brown or greenish. Lower surfaces are typically ''without'' a cortex (unlike other foliose lichens),Fioliose lichens, Lichen Thallus Types, Allan Silverside
/ref> and cottony, often with fungal hyphae fused to form a network of veins. The reproductive structures isidia, soredia or may be present in some species. All species of ''Peltigera'' associate with the nitrogen-fixing cyanobacteria ''Nostoc''.

''Peltigera'' can be distinguished from the equally large and leaf-like lichen, ''Nephroma'', by its veined lower cortex; ''Nephroma'', by contrast, has a smooth, unveined lower cortex.

Habitat

''Peltigera'' are mainly ground-dwelling, but can also be found on mosses or dead wood. Some species are used as forest succession indicators.

Taxonomy

In 1753, Linnaeus first described the species ''Lichen apthosus'' and ''L. caninus'' back when all known lichens were grouped into the genus ''Lichen''. Later, in 1787, Willdenow circumscribed the genus ''Peltigera'', and redescribed '' P. aphthosa'' and '' P. canina''.

The generic name is derived from the Latin language ''pelta'' (small shield), and refers to the shield-shaped thallus in these species. The common name, the dog lichen, refers to the perceived resemblance of ''P. caninus'' to a dog.

Phylogeny

In a comparative analysis of both morphological and chemical characteristics as well as sequences of large subunit nuclear ribosomal DNA, it was shown that the genus ''Peltigera'' is monophyletic. Several species, such as '' P. canina'', have been changed to a group as there appears to be several species clustered under a single name.

Recent taxonomic work has led to the consolidation of three previously recognized aquatic ''Peltigera'' species ('' P. hydrothyria'', ''P. gowardii'', and ''P. aquatica'') into a single species with three varieties. According to Bruce McCune and Daphne Stone (2022), while molecular analysis showed three distinct genetic clades, maintaining them as separate species proved impractical for conservation and research purposes. This was because ''P. gowardii'' and ''P. aquatica'', which occur together in western North America, are indistinguishable without DNA sequencing. The difficulty in identifying specimens to species level effectively stalled data collection, with most specimens remaining classified only as ''P. hydrothyria'' sensu lato. To resolve this issue while preserving information about genetic diversity, the three taxa were reclassified as ''P. hydrothyria'' var. ''hydrothyria'' (eastern North America), ''P. hydrothyria'' var. ''gowardii'' (western), and ''P. hydrothyria'' var. ''aquatica'' (western). This taxonomic solution allows for practical field identification while still acknowledging the genetic differences between populations.

Distribution

The ''Peltigera'' have a widespread distribution, and are found on all continents. There are 34 North American species, 30 European species, 25 species from South America, and 16 species from New Zealand. There are 27 ''Peltigera'' species that have been recorded from China.

Ecology

''Peltigera'' lichens serve as important hosts for diverse microbial communities, functioning as miniature ecosystems rather than simply dual symbiotic partnerships. Recent research has revealed that ''Peltigera'' species harbour rich communities of basidiomycete yeasts, with some species supporting multiple distinct yeast taxa within their thalli. For example, '' P. rufescens'' has been found to host over 90 different yeast isolates representing 18 distinct taxa, demonstrating the complexity of these microbial associations. These lichens appear to acquire key microbial symbionts directly from the soils where they grow, suggesting their local environments serve as reservoirs for their microbiome diversity.

The yeasts associated with ''Peltigera'' belong to several major taxonomic groups, including members of the classes Tremellomycetes, Cystobasidiomycetes, and other basidiomycetes. Many of these yeasts are psychrotolerant, showing adaptations to cold environments, which may enhance the lichens' ability to survive in harsh conditions. This characteristic likely contributes to the successful colonisation of various habitats by ''Peltigera'' species, particularly in temperate and cold regions where they are commonly found. Studies have shown that these yeasts can maintain metabolic activity even at low temperatures, potentially supporting the lichen's overall survival and ecological functionality.

The relationship between ''Peltigera'' and its microbial communities appears to vary across different environments and species. Research in southern Chile has demonstrated that ''Peltigera'' lichens can significantly enhance gamma diversity across landscapes by functioning as island-like habitats that support specialised bacteria and yeasts. This suggests that ''Peltigera'' species play a broader ecological role beyond their own survival, contributing to local microbial biodiversity patterns and ecosystem processes. While the specific functions of many associated microorganisms remain under investigation, this complex microbial diversity likely contributes to the ecological resilience of ''Peltigera'' species across different environments and may help explain their successful colonisation of diverse habitats worldwide.

Species

*''Peltigera alkalicola'' – Tanzania
*''Peltigera aphthosa''
*''Peltigera appalachiensis''
*''Peltigera asiatica''
*''Peltigera borealis''
*''Peltigera borinquensis''
*'' Peltigera britannica''
*''Peltigera canina''
*'' Peltigera castanea''
*''Peltigera chabanenkoae''
*'' Peltigera chionophila'' – North America
*''Peltigera cinnamomea'' – northwestern North America
*''Peltigera clathrata''
*'' Peltigera collina''
*'' Peltigera degenii''
*'' Peltigera didactyla''
*'' Peltigera dilacerata''
*'' Peltigera dolichorhiza''
*'' Peltigera elisabethae''
*''Peltigera elixii''
*''Peltigera esslingeri''
*''Peltigera evansiana''
*'' Peltigera extenuata''
*''Peltigera fibrilloides''
*'' Peltigera fimbriata'' – Papua New Guinea
*''Peltigera flabellae''
*''Peltigera frigida''
*''Peltigera frippii'' – Norway
*''Peltigera gallowayi''
*''Peltigera globulata''

*'' Peltigera granulosa'' – Papua New Guinea
*''Peltigera hawaiiensis''
*''Peltigera hokkaidoensis''
*''Peltigera holtanhartwigii''
*'' Peltigera horizontalis''
*''Peltigera hydrophila'' – Chile
*'' Peltigera hydrothyria''
*'' Peltigera hymenina''
*'' Peltigera isidiophora'' – China
*'' Peltigera islandica'' – Iceland
*''Peltigera itatiaiae''
*'' Peltigera koponenii'' – Papua New Guinea
*'' Peltigera kristinssonii'' – Iceland
*''Peltigera kukwae''
*'' Peltigera lactucifolia''
*'' Peltigera lairdii'' – Antarctica
*'' Peltigera latiloba'' – Alaska (USA); Norway
*'' Peltigera lepidophora''
*'' Peltigera leptoderma''
*''Peltigera leucophlebia''
*'' Peltigera malacea''
*''Peltigera massonii''
*''Peltigera melanorrhiza''
*'' Peltigera membranacea''
*''Peltigera mikado''
*'' Peltigera montis-wilhelmii'' – Papua New Guinea
*'' Peltigera neckeri''
*'' Peltigera neodegenii'' – China
*''Peltigera neopolydactyla''
*'' Peltigera neorufescens''
*''Peltigera nigriventris''
*''Peltigera occidentalis''
*''Peltigera orientalis''
*'' Peltigera pacifica'' – Canada
*'' Peltigera papuana'' – Papua New Guinea
*''Peltigera phyllidiosa''
*'' Peltigera polydactylon''
*'' Peltigera ponojensis''
*''Peltigera praetextata''
*'' Peltigera pulverulenta''
*'' Peltigera pusilla''
*''Peltigera rangiferina''
*'' Peltigera retifoveata'' – Finland
*'' Peltigera rufescens''
*''Peltigera rufescentiformis''
*'' Peltigera scabrosa''
*'' Peltigera scabrosella'' – Norway
*'' Peltigera seneca''
*'' Peltigera serusiauxii''
*'' Peltigera shennongjiana'' – China
*''Peltigera sipmanii''
*'' Peltigera sorediifera''
*''Peltigera stanleyensis''
*'' Peltigera subhorizontalis''
*'' Peltigera tartarea''
*'' Peltigera tereziana''
*'' Peltigera ulcerata''
*'' Peltigera vainioi''
*'' Peltigera venosa''
*''Peltigera vitikainenii''
*'' Peltigera weberi'' – Papua New Guinea
*''Peltigera willdenowii''
*'' Peltigera wulingensis'' – Canada; China; Norway; Russia

Uses

''Peltigera'' species have been used historically to treat wounds, urinary disorders, thrush, tuberculosis, and rabies. '' P. apthosa'' was used as a remedy for cough and infantile aphthae.
''P. furfuracea'' has shown potent antioxidant activity and reducing power. Similarly, ''Peltigera'' specimens from Hawaii and Iceland have also been reported to show pronounced antioxidant activity.

Food source

Although a few reports have described caribou and reindeer feeding on the thalli of ''Peltigera'', in general, species of ''Peltigera'' are not commonly used as a food source by mammals. A study of the grazing habits of the land snails '' Cantareus aspersa'' and ''Limax'' species revealed that these snails prefer to eat ''Peltigera'' species (such as '' P. praetextata'') that are lacking in secondary metabolites.

Bioactive compounds

''Peltigera leucophlebia'' contains the compounds tenuiorin and methyl orsellinate, which are inhibitory to the enzyme 15-lipoxygenase. Tenuiorin is also known to occur in '' P. apthosa'', '' P. malacea'' and '' P. neckeri''. A mixture of methyl and ethyl orsellinates have been identified from ''P. aphthosa'' that had antibacterial activity against Gram-positive and -negative bacteria. The novel non-protein amino acids solorinine and peltigerine have been detected in various species of ''Peltigera''.

References

Further reading

Gilbert, O. ''Lichens Naturally Scottish.'' 2004. Scottish Natural Heritage.

{{Taxonbar, from=Q2716168

Lichen genera
Peltigerales genera
Taxa described in 1787
Taxa named by Carl Ludwig Willdenow