Dog Lichen

Dog Lichen sprawls across mossy ground in loose, overlapping sheets of broad, thin lobes that can each be several centimetres wide. Wet, it is soft and pliable and turns a deep slate grey-brown; dry, it stiffens, pales and curls its margins upward to reveal the pale veined underside.

The genus Peltigera, in the family Peltigeraceae, is often called the pelt lichens because of that hide-like texture. P. canina is the classic representative of the group whose main photobiont is the cyanobacterium Nostoc, which is why the thallus is grey to brown rather than the bright green of the algal-partnered pelts.

The common name comes from the upturned, tooth-like fruiting bodies at the lobe tips, historically likened to a dog's teeth. Like several of its relatives it is a broad concept — a handful of very similar downy, shaggy-rhizined species have been separated from it, so field records are often best given as the P. canina group.

Thallus

Foliose and loosely attached, forming irregular rosettes or spreading patches 5–20 cm or more across. Lobes are broad, rounded and thin, 1–3 cm wide, with wavy, often upturned margins.

Upper surface

Grey-brown, brownish or bluish grey when moist, drying to pale grey-buff. Young lobes and lobe margins are covered in a fine felt of short hairs (tomentum), which is best seen with a hand lens against the light and is one of the key characters. Soredia and isidia are absent.

Lower surface

White to cream, with a network of broad, raised, pale to brownish veins that darken toward the lobe centre. Long, pale, shaggy rhizines up to a centimetre or more grow from the veins in tufts and anchor the lichen to moss and soil.

Apothecia

Borne on narrow upturned extensions of the lobe tips, reddish brown to dark brown, saddle-shaped and rolled so that they stand vertically like small teeth or flags. The medulla is white and the thallus tears easily when wet.

Dog Lichen grows over soil, moss, turf and rotting organic matter rather than on bare rock or bark. Typical sites are mossy lawns and churchyards, sand dunes and dune slacks, calcareous grassland, heath edges, roadside banks, path sides and open woodland floors, always where competing vascular vegetation is thin.

It is widespread across the temperate and boreal northern hemisphere, common in Europe and North America, and is one of the lichens most likely to be encountered at ground level in ordinary settled landscapes. Perennial and evergreen, it is at its most conspicuous and supple after prolonged autumn and winter rain, and shrinks to inconspicuous grey scraps in summer drought.

The fungal partner encloses colonies of the nitrogen-fixing cyanobacterium Nostoc, which supplies both carbon from photosynthesis and fixed nitrogen. That nitrogen-fixing capacity makes the Dog Lichen group ecologically important on nutrient-poor soils, dunes and disturbed ground, where it enriches the substrate as fragments break down.

It is a ground-dwelling pioneer that establishes over mosses and thin soil crusts, binding loose sand and mineral particles with its rhizines and helping stabilise dune and bank surfaces. Reproduction occurs through ascospores released from the upturned marginal apothecia and, very effectively, through detached lobe fragments that re-root by rhizines where they land.

Peltigera membranacea is extremely similar and shares the downy surface and shaggy rhizines, but is thinner and floppier with a more translucent, papery texture and finer, more branched rhizines. Peltigera praetextata has the same general form but bears small scale-like regrowths (isidia-like phyllidia) along cracks and lobe margins, which P. canina lacks.

Peltigera rufescens is smaller and more tightly curled, with narrow, upturned, crisped lobes and a densely tomentose surface, forming rosettes on dry calcareous ground. Peltigera aphthosa and P. leucophlebia are unmistakable when moist because they turn bright grass green and carry dark wart-like cephalodia on the upper surface, features never seen on Dog Lichen. Peltigera horizontalis has flat-lying, horizontally oriented reddish apothecia rather than upright saddle-shaped ones.