Tree Lungwort

Tree Lungwort (Lobaria pulmonaria) is a large foliose lichen in the family Peltigeraceae and one of the most visually striking epiphytes of temperate woodland. Mature thalli can spread 10-30 cm across a trunk, forming broad leathery rosettes of lobes that hang loosely from the bark.

Its most quoted feature is the surface texture: the upper side is thrown into a network of raised ridges enclosing sunken pits, a reticulate pattern that early naturalists compared to the alveoli of a lung, giving the species both its common and its scientific name.

Lobaria pulmonaria is also biologically unusual because it is a tripartite lichen. In addition to the fungus and a green algal partner, it houses cyanobacteria in small internal warts called cephalodia, allowing the thallus to fix atmospheric nitrogen as well as photosynthesise. It is widely treated by ecologists as an indicator of ancient, continuously wooded, clean-air habitat.

Thallus and lobes

The thallus is foliose and loosely attached, with broad, rounded to antler-like lobes 1-3 cm wide that often have shallowly notched or forked tips. Whole thalli are commonly 10-20 cm across and can be considerably larger on old trees, hanging in loose leathery sheets.

Upper surface

The upper surface carries a pronounced reticulate network of raised ridges and sunken depressions. Colour is strongly moisture-dependent: bright grass-green to olive-green when wet, drying to a dull greenish-brown, grey-brown or tan. Soredia and isidia — granular vegetative propagules — accumulate along the ridges and lobe margins in most populations.

Lower surface

The underside is pale buff to brown, matching the ridge pattern in reverse (raised where the top is sunken) and bearing scattered patches of short brown tomentum, with pale bald spots on the raised areas.

Fruiting bodies

Apothecia are produced only occasionally: reddish-brown to chestnut discs with a thin thalline rim, sitting on the ridges and lobe margins. Most reproduction is vegetative, via soredia and isidia.

Tree Lungwort grows chiefly on the trunks and major limbs of mature broadleaf trees — oak, ash, maple, beech, sycamore, hazel and willow are all frequent hosts — and less often on conifers or on mossy rock in very humid sites. It requires high atmospheric humidity, good but not harsh light, and a long period of habitat continuity, so it concentrates in old-growth forest, wooded ravines, upland ravine woodlands and ancient parkland.

The species has a wide circumboreal to temperate distribution across Europe, Asia, North America and parts of Africa, but has declined sharply in lowland and industrial regions and now survives mainly in western and upland areas with clean, moist air. It is perennial, persisting on the same tree for decades, and can be found in any season, appearing greenest after rain.

Lobaria pulmonaria is an epiphyte, using bark purely as a substrate and taking no nourishment from its host. Its tripartite structure — mycobiont, green alga and cyanobacteria in cephalodia — lets it both photosynthesise and fix atmospheric nitrogen, so it makes a measurable contribution to the nitrogen budget of the forests where it is abundant, releasing nitrogen-rich material to the soil as fragments fall.

Dispersal is mostly by soredia and isidia and by whole thallus fragments detached in storms, which establish poorly over long distances. Combined with slow growth and sensitivity to air quality and drying, this makes colonisation of new woodland extremely slow, which is precisely why the species is used as a signal of long-unbroken woodland cover.

Other Lobaria species are the main confusion. Lobaria scrobiculata is greyer to blue-grey, has a shallower, more wrinkled rather than sharply ridged surface, and is a bipartite cyanobacterial lichen. Lobaria virens (L. laetevirens) is a smoother, glossier, brighter green species with only faint ridging and usually abundant apothecia, and lacks the deep pitted network.

Sticta species share the leathery lobed habit and humid old-woodland habitat but are separated by round white to brown pores (cyphellae) on the lower surface, which Lobaria never has. Large Peltigera species are also lobed and loosely attached but grow mostly over soil and moss rather than up tree trunks, have prominent raised veins and root-like rhizines beneath, and lack the reticulate upper-surface ridging.