Whitish-green to bluish-gray above and black below, Parmelia sulcata is one of the most common lichens worldwide. Its upper surface is covered in a distinctive network of white, angular cracks (pseudocyphellae) filled with powdery soredia, giving it the “hammered” appearance that inspires its common name. The short, perpendicularly branched rhizines hold it closely appressed to bark.
One of the earliest colonizers on outer branches of oak, it serves as an intermediate nitrogen sensitivity indicator. Its ubiquity makes it an important baseline species for air quality monitoring studies across Europe and North America.
Unmistakable for its distinctive yellow-green colour, Flavoparmelia caperata is one of the most common foliose lichens in eastern North America. The wrinkled upper surface bears granular soredia, giving older specimens a rough, mealy texture. It grows loosely attached to the bark of deciduous trees, often forming broad rosettes.
Like Parmelia sulcata, it is an intermediate nitrogen indicator, present in moderately enriched environments but absent from the most polluted sites.
Bright orange to yellow-orange and impossible to overlook, Xanthoria parietina produces abundant orange apothecia and gets its vivid colour from anthraquinone pigments that act as a sunscreen. It thrives on bark, rock, and concrete, especially near coasts and farms where nitrogen enrichment is high.
Unlike most lichens that decline with pollution, X. parietina is a nitrogen-loving species that actually increases in enriched and polluted areas. It tolerates maritime salt spray and is often the dominant lichen on coastal structures and farm buildings.
Green when moist and brownish when dry, Lobaria pulmonaria is a large, deeply ridged lichen whose surface texture resembles lung tissue — a resemblance that led medieval herbalists to prescribe it for respiratory ailments under the Doctrine of Signatures. Cephalodia on the lower surface house cyanobacteria that fix atmospheric nitrogen.
This tripartite lichen (fungus + green alga + cyanobacteria) is a prized indicator of old-growth forest continuity and clean air. It is declining across much of its range due to habitat loss and air pollution, and is legally protected in several European countries.
Deep blue-gray when wet and lighter with a yellow tinge when dry, Lobaria scrobiculata features round soralia set among a loose network of ridges on its upper surface. The underside is cream to light brown and covered in a fine tomentum.
Found on the bark of hardwoods and shrubs in moist forests, it shares its larger cousin’s preference for clean, humid environments and old-growth conditions.
A large, blue-green to brown-green lichen that sprawls over moss on the ground, logs, rocks, and tree bases in damp forests. The upper surface is weakly ridged with a fine tomentum, while tawny brown apothecia curl upward on raised lobe tips, sometimes likened to a dog’s tongue, hence the common name.
Turn it over and you will find one of its most distinctive features: a network of raised veins covered in velvety tomentum, anchored by long, unbranched rhizines. These veins help channel water across the lower surface.
Brownish-green to grayish, Peltigera collina produces soredia along its lobe margins and brownish-black apothecia on raised lobe tips. The underside has brownish veins and variable rhizines that are often plumose (feathery).
Common on the bark of shrubs and hardwoods and often found growing over moss in moist forests, it is one of the more frequently encountered Peltigera species in temperate regions.
Bluish-white to greenish-gray and loosely attached to bark, Parmotrema perlatum has sparse black marginal cilia and small, crescent-shaped soralia near its lobe tips. The underside is black at the centre, becoming lighter toward the margins.
Fairly common in moist forests, it is used in traditional Indian cuisine as “kalpasi” or “dagad phool”, a spice valued for its earthy, musky aroma in meat dishes and biryanis.
Grayish to pale green with a messy, tufted appearance, Platismatia glauca lacks the distinct network of ridges found in many foliose species. It may bear isidia, soredia, or both, and its underside is a patchy, variable mix of black, brown, and white.
Common on bark (especially conifers), it is frequently found on the forest floor after storms, torn from the canopy by wind and rain. Its ragged, somewhat dishevelled look makes it easy to recognize once you know what to look for.
Similar to P. glauca but with narrower, longer lobes that occasionally droop from branches. Isidia line the lobe margins rather than the upper surface. Found on bark of conifers in moist forests, it adds to the draped, festooned character of old temperate rainforest canopies.
Gray above and distinctively white below, Physcia species form small, neat rosettes on bark. They often bear soredia or isidia at the lobe tips and are among the first lichens many beginners learn to recognize.
Nitrogen-tolerant and even nitrogen-loving, they thrive in nutrient-enriched environments where more sensitive species have vanished, making them useful markers of agricultural runoff and urban nitrogen deposition.
Brownish-green to bluish-brown, Nephroma helveticum is a low-growing lichen with smooth lobes decorated by many marginal and laminal lobules. Its most unusual feature is the placement of its orange-brown apothecia: they appear on the underside of the lobe tips, visible only when the lobes curl upward.
Found on the bark of shrubs and hardwoods, often over moss, it is an indicator of moist, mature forest conditions.
Gray-green above with a distinctive black, shiny underside, Hypogymnia physodes has inflated, hollow lobes that burst open at the tips to reveal powdery soredia inside, one of its key identification features. Unlike most foliose lichens, it lacks rhizines entirely and attaches to its substrate by a holdfast or simply by lying against bark.
Widespread and common across the Northern Hemisphere on tree bark and occasionally on rock, it is one of the most frequently used lichens in air quality biomonitoring studies. Its tolerance range sits between the most sensitive species and the hardiest nitrogen-lovers, making it a useful middle-of-the-road indicator.
Intensely orange to red-orange, Rusavskia elegans forms brilliant rosettes on rock surfaces, particularly where birds perch. It is one of the most brightly coloured lichens in the world and a familiar sight on mountain summits and coastal cliffs.
Formerly known as Xanthoria elegans, it has been used as a model organism for lichenometry — dating rock surfaces by measuring lichen diameter growth.
Gray to blue-gray with distinctive white spots (pseudocyphellae) scattered across its upper surface, Punctelia rudecta is one of the most common foliose lichens on trees in eastern North America. The name ‘Punctelia’ refers to these punctiform white markings.
Moderately pollution-tolerant and expanding its range as air quality improves. Its C+ red reaction produces one of the most vivid colour changes in field chemistry.
Pale gray to white with narrow, radiating lobes forming neat star-shaped rosettes, Physcia stellaris is a small but common lichen on deciduous tree bark. It frequently produces dark brown to black apothecia with a conspicuous white rim.
One of the few common foliose lichens that reproduces primarily by sexual spores rather than vegetative fragments — most of its relatives rely on soredia instead.
Large, leathery, single-lobed plates attached to rock by a single central point, Umbilicaria mammulata is one of the largest lichens in eastern North America, with individual thalli often reaching 15–30 cm across.
Famous as an emergency food — Indigenous peoples and early European explorers boiled it extensively to make a gelatinous, nutritious survival food. Individual thalli may be centuries old.
Yellow-green to olive-green rosettes tightly appressed to rock surfaces, Xanthoparmelia cumberlandia is one of the most common foliose rock lichens in eastern North America. It forms neat, circular thalli 3–15 cm in diameter on exposed boulders.
The genus Xanthoparmelia contains over 800 species worldwide — one of the largest lichen genera. Almost all grow on rock, never on bark.
Small, bright orange to yellow-orange with distinctive hood-shaped soralia at the lobe tips, Xanthomendoza fallax is a common nitrogen-loving lichen on deciduous trees. The lobe curls over to form a hood beneath which soredia accumulate.
The species name “fallax” means deceptive — it was long confused with other small orange species. One of several orange lichens increasing with atmospheric nitrogen deposition.
Tiny lemon- to egg-yolk-yellow rosettes, rarely more than 1 cm across, often merging into scattered yellow patches along the rain tracks and branch forks of roadside trees. Candelaria concolor is one of the commonest small yellow lichens on town trees in North America and is spreading in Britain.
Its lobes are minute (about 1 mm long and 0.2–0.5 mm wide), finely divided and scalloped. The lobe margins break down into yellow granules and coarse soredia, so older colonies can look like a yellow crust. The underside is whitish, with scattered white rhizines.
Pale grey to blue-grey, often browner at the lobe tips, Parmelia saxatilis has the same network of raised white lines (pseudocyphellae) as P. sulcata, but along that network it grows tiny, dark-tipped cylindrical isidia instead of powdery soredia. It is common on acid rocks, walls and trees across Britain and much of Europe.
Lobes are up to about 3 mm wide and widen slightly at the tips. The underside is black, paler at the margin, with simple rhizines. Dark red-brown apothecia up to 1 cm across are occasional.
Bright, almost apple-green when wet and pale smoky grey-green when dry, Peltigera aphthosa forms broad leafy lobes over moss and soil on forest floors. Its upper surface is dotted with small dark "freckles": cephalodia, pockets of nitrogen-fixing Nostoc cyanobacteria.
Its main photosynthetic partner is a green alga (Coccomyxa), which is why it is vivid green rather than the grey or brown of most other Peltigera. The cephalodia add nitrogen fixation, so one lichen draws both carbon and nitrogen from the air.
