Peltigera


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, but can also occur on moss, trees, rocks, and many other substrates 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. The color of the upper surface may range from drab gray, brown or greenish. Lower surfaces are typically without a cortex, 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, Carl Linnaeus first described the species Lichen apthosus and L. caninus back when all known lichens were grouped into the genus Lichen. Later, in 1787, Carl Ludwig Willdenow circumscribed the genus Peltigera, and redescribed P. aphthosa and P. canina.
The generic name is derived from the Latin language pelta, 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 into a single species with three varieties. According to Bruce McCune and Daphne Stone, 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, P. hydrothyria var. gowardii, and P. hydrothyria var. aquatica. 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 host diverse microbial communities, functioning as miniature ecosystems rather than simple dual partnerships. A cross-continental metabarcoding study found that geography, rather than host identity, explained more of the variation in the fungal community within the thallus ; Peltigera also showed a "nested" pattern, with many thalli sharing a common subset of resident fungi. The assemblage was mostly Ascomycota with a consistent Basidiomycota component, and a small recurring core that included the basidiomycete yeast Cutaneotrichosporon debeurmannianum alongside Dothideomycete and Chaetothyriomycete lineages. Consistent with this, other work shows that Peltigera species harbour rich communities of basidiomycete yeasts; for example, P. rufescens has yielded over 90 yeast isolates representing 18 taxa, and soils appear to act as local reservoirs from which these symbionts are acquired.
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 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 jonii – Europe
  • Peltigera koponenii – Papua New Guinea
  • Peltigera kristinssonii – Iceland
  • Peltigera kukwae
  • Peltigera lactucifolia
  • Peltigera lairdii – Antarctica
  • Peltigera latiloba – Alaska ; 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.