Peltigera aphthosa

Green Dog Lichen

Flora, fauna, earth, and sky...
The natural history of the northwoods


  • Peltigera, from the Latin
  • aphthosa, from the Latin
  • Common Name, from
  • Other common names include: Leafy Lichen


  • aceae, the family



  • A foliose lichen with a large thallus, sometimes over 3' across. Individual lobes up to 4" long and 2.5" broad.
  • Thallus bright green when moist; pale smoky green when dry. Upper surface covered with small cephalodia. Apothecia are large and common. The mycobiont (Ascomycete) comprises the bulk of the thallus; the algal component constitutes only 3%-5% of the volume of the structure.
  • Has two photosynthetic members: a green alga of genus Coccomyxa, and a blue-green cyanobacteria of genus Nostoc. Both are capable of fixing carbon dioxide photosynthetically, which may be of competitive advantage in some habitats. The Nostoc member is contained in the cephalodia and is capable of nitrogen fixation.


  • Circumpolar species in arctic, boreal, and temperate zones. In North America throughout Canada and Alaska; south to the Pacific Northwest, the Southwest, the Great Lakes states, New England, and in the Appalachians to North Carolina.


  • Like all lichens very dependent on high relative humidity; abundance is generally in direct relation to the relative humidity. Because of ability to take up moisture from the air, underlying soil is not as important a source of moisture as it is to vascular plants.
  • Can grow on shallow, sterile soils. Most commonly occurs on soil, rock, humus, moss, or fallen logs; more rarely in dry woodlands.
  • Better adapted to cold climates than any other life form.
  • Can endure more shade than most lichens but grows best in direct sun.
  • Lichens in general decline in productivity and quality in older stands.
  • Lichens may be pioneer plants on some sites because they are dependent on air moisture rather than soil moisture, and can tolerate shallow soils. They persist in environments too harsh for higher plants, provided relative humidity is sufficiently high for lichen growth and temperature is sufficiently low to inhibit competitors. Northern boreal forests offer optimal conditions for lichen growth because of slow rates of plant succession and little competition from other plant forms.
  • Occurs in various habitats, including open and closed coniferous forests, lichen woodlands, bogs, and sedge tussocks.
  • A dominant ground cover in White Spruce (Picea glauca) habitats.
  • Can fix nitrogen; optimum fixation occuring in autumn at temperatures of 68-86 degrees F. The ability to fix nitrogen is extremely reduced at an atmospheric pH below 6.0, and reduced fixation rates may be an indicator of acid rain. Acid rainfall may severely inhibit nitrogen fixing activity and, as a result, reduce or eliminate its contribution of fixed nitrogen to the forest ecosystems where it is abundant.
  • Lichens widely used as indicators of air pollution or air quality. Peltigera aphthosa is extremely susceptible to air pollution, especially from sulfur dioxide and fluorides. Lichens also absorb radioactive fallout more readily than vascular plants;.this material is then passing along the foodchain.


  • Does not generally occur in recently burned areas. Like other lichens, highly flammable under dry conditions due to drying out when relative humidity drops. Commonly growing on humus or moss, rendering it highly liable to destruction by fire.
  • Peltigera often establish in moss mats within 5 years following fire. In burned areas, may occur in the most lightly burned or unburned spots, and then spread out vegetatively.
  • Lichens often serve as an initial point of ignition in woodlands and tundra, and have an essential role in the spread of fire. Lichens dry rapidly during periods of low relative humidity because of their absence of roots and water storage tissue, and low resistance to water loss. Dry lichens resemble dead litter more than live tissue in their susceptibility to fire. Continuous lichen mats present an uninterrupted surface along which fire spreads. They typically accumulate tree and shrub litter, which adds to their flammability.
  • Lichens grow slowly and mats may take 70-100 years to regain former abundance. However, some situations fire may increase lichen cover, especially where a thick moss carpet has developed. In the northern boreal lichen belt, lichen mats may be increased by burning sphagnum peatlands or black spruce muskegs and forests. Fires in these communities result in lichen mats in some 40-50 years. Because black spruce and mosses occur in later stages than do lichens, good lichen growth can persist for at least 100 years.





  • Lichen reproduction mainly occurs by means of thallus fragmentation or the dispersal of isidia and soredia. Wind, water, or animals play an important role in the dispersal of these vegetative propagules. Peltigera aphthosa also produces many large apothecia.




Boreal border
Last updated on 11 September 1998