Lettuce lichen looks like a handful of crumpled salad greens stuck to a tree. It is a large, leafy lichen with broad, loosely attached lobes that are distinctly yellowish green on top, and the lobe edges are fringed with many tiny leafy outgrowths that add to its ruffled look. It lives on the bark of conifers, often well above the ground, so a piece that has fallen to the forest floor is the easiest way to get a close look.
Every lichen is a partnership between a fungus and a partner that makes food from sunlight. In lettuce lichen that partner is a green alga, but the lichen also carries cyanobacteria, which can turn nitrogen from the air into a form plants can use. A Forest Service research report described it as the main nitrogen-fixing lichen of old-growth conifer forests in the Northwest, and in old stands it can build up to around a ton per hectare. Lichens like this add nitrogen to the soil when they fall and break down.
Lettuce lichen is closely tied to old forests, but not because it cannot grow in young ones. Transplanted pieces grow as well or better in younger stands. It is simply slow to spread to new places. It is also sensitive to air pollution. Look for it in old, moist conifer forest at low and middle elevations.
How to identify it
A large, loosely attached leafy lichen with broad lobes that are distinctly yellowish green on top and have a fuzzy underside. The lobe edges are fringed with many tiny lobules. It grows on conifer bark and is often found as fallen clumps on the forest floor.
Look-alikes
Lungwort lichen is similar in size and shape but is bluish or bright green rather than yellowish green, has no lobules along its edges, and carries tiny powdery or grainy bumps on its surface.
Habitat
On the bark of conifers, especially large old trees, in humid old-growth and older forests. It is most abundant in old forests at roughly 1,300 to 3,300 feet, though small amounts turn up in younger stands.
Sightings in the forest
139 research-grade sightings in Mt. Hood National Forest on iNaturalist, most recently on September 25, 2026. See them on iNaturalist →