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.
