Tree lungwort

Appearance

It is a foliose lichen and its leaf-like thallus is green, leathery and lobed with a pattern of ridges and depressions on the upper surface. Bright green under moist conditions, it becomes brownish and papery when dry.

This species often has a fine layers of hairs, a tomentum, on its lower surface. The cortex, the outer protective layer on the thallus surface, is roughly comparable to the epidermis of a green plant.

The thallus is typically 5–15 centimetres in diameter, with individual lobes 1–3 centimetres wide and up to 7 cm long. The asexual reproductive structures soredia and isidia are present on the thallus surface.

Minute cephalodia—pockets of cyanobacteria—are often present on the lower surface of the thallus; these spots are conspicuously darker than the green surface of the thallus. Like other foliose lichens, the thallus is only loosely attached to the surface on which it grows.

Distribution

It has a wide distribution in Europe, Asia, North America and Africa, preferring damp habitats with high rainfall, especially coastal areas.

Status

Due to declining population, ''L. pulmonaria'' is considered to be rare or threatened in many parts of the world, especially in lowland areas of Europe. The decline has been attributed to industrial forestry and air pollution, particularly acid rain. ''L. pulmonaria'', like other lichens containing a blue-green algal component, are particularly susceptible to the effects of acid rain, because the subsequent decrease in pH reduces nitrogen fixation through inhibition of the algal nitrogenase enzyme.

Reproduction

''L. pulmonaria'' has the ability to form both vegetative propagation and sexual propagules at an age of about 25 years.

In sexual reproduction, the species produces small reddish-brown discs known as apothecia containing asci, from which spores are forcibly released into the air. Based on studies of ascospore germination, it has been suggested that ''L. pulmonaria'' spores use some mechanism to inhibit germination—the inhibition is lifted when the spores are grown in a synthetic growth medium containing an adsorbent like bovine serum albumin or α-cyclodextrin.

Dispersal by vegetative propagules has been determined as the predominant mode of reproduction in ''L. pulmonaria''. In this method, the protruding propagules become dry and brittle during the regular wet/dry cycles of the lichen, and can easily crumble off the thallus. These fragments may develop into new thalli, either at the same locale or at a new site after dispersal by wind or rain.

A number of steps are required for the development of the vegetative propagules, including the degeneration of the thallus cortex, replication of green algal cells, and entanglement of fungal hyphae with the green algal cells. This steps lead to an increase in internal pressure which eventually breaks through the cortex. Continued growth leads to these granules being pushed upwards and out of the thallus surface.

Uses

''L. pulmonaria'' has also been used to produce an orange dye for wool, in the tanning of leather, in the manufacture of perfumes and as an ingredient in brewing.