Lichen Biology

Growth Forms

Pseudocyphellaria rainierensis, old-growth specklebelly.
Pseudocyphellaria rainierensis, old-growth specklebelly. This species has two clearly defined upper and lower sides as well as fringed lobes and many vegetative reproductive structures called "isidia". Photo by Karen Dillman, U.S. Forest Service.

There are three main types of lichens:

  1. Foliose
  2. Fruticose
  3. Crustose

Foliose Lichens

Foliose lichens have two easily distinguishable sides. In other words, there is a top side and there is a bottom side. They can be very flat, leafy like lettuce, or convoluted and full of ridges and bumps.

Fruticose Lichens

Fruticose lichens can be pendant and hair-like, upright and shrubby, or upright and cup-like. Many fruticose lichens have round branches that have a central core and others are hollow in the middle. Other fruticose lichens have flat branches that tangle up with each other.

Cladonia fimbriata, trumpet lichen.
Cladonia fimbriata, trumpet lichen. Notice the cup-like stalks. Photo by Charles Peirce, Michigan Wildflowers.

Usnea longissima, old man’s beard.
Usnea longissima, old man’s beard. This rare lichen hangs from a central stalk and can get up to several feet in length. Its habitat is shrinking and instead of establishing itself via spores, parts of it break off and reestablish elsewhere. It is a strong indicator species of air pollution. Photo by Karen Dillman, U.S. Forest Service.

Ramalina subleptocarpa.
Ramalina subleptocarpa. This is an example of a fruticose lichen with two-sided flat branches. Since these branches are not distinctive (no top or bottom), this is still considered fruticose. Photo by Karen Dillman, U.S. Forest Service.

Crustose Lichens

Crustose lichens are just that, crusts. They form a crust over a surface, like a boulder, the soil, a car, or your roof shingles. They can come in many bright, vibrant colors like sunny yellow, orange, and red, as well as grays and greens. Crustose lichens are pressed against their substrate.

colorful crustose lichens on a rock.
Many colorful crusts on a rock. Photo by Larry St. Clair.

Lecanora garovaglii, gray crust.
Lecanora garovaglii, gray crust, with other crusts, on a rock. Photo by Chris Wagner, U.S. Forest Service.

Pleopsidium chlorophanum, yellow crust.
Pleopsidium chlorophanum, yellow crust, with other crusts, on a rock. Photo by Chris Wagner, U.S. Forest Service.

Next: Lichen Reproduction…