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Written by Laura H., Somerset County Rutgers Master Gardener
Walking in a park, I often study tree bark and, not infrequently, find it patched with lichen. What is lichen, actually? Well, it can be tricky to classify, as lichen is composed of two or more different species which inhabit one organism. Typically, a fungus is the dominant species and primarily responsible for the physical characteristics of the lichen. The fungus composes about 80% of the body of the lichen, and absorbs moisture, takes in minerals from the air, and provides protection and support. In lichens, fungi are paired with algae, and occasionally cyanobacteria. The function of algae and cyanobacteria is to produce food via photosynthesis for the lichen. The fungi’s scientific name is adopted as the lichen’s genus name, while the species name is typically a Latin term which describes the lichen in some manner.
There are over 13,000 species of lichens around the world. They thrive in moderate temperate zones with enough moisture and light to meet their needs. Certain lichen species have adapted to extreme environs, such as desert, arctic, and mountainous terrain. Air pollution, though, is something that most lichens cannot tolerate easily; they act as leading indicators of unacceptable levels of atmospheric toxins.
There are three primary categories of lichens, based on their features and forms: crustose, or crust-like; foliose, or leaf-like; and fruticose, or bush-like. Younger trees tend to have smooth bark, which facilitates the growth of crustose lichen. Older trees, with uneven surfaces, are more likely to attract the faster-growing foliose and fruticose varieties. Lichens prefer deciduous trees over conifers, as deciduous trees allow more needed light to enter, especially during the winter months. Coniferous trees’ greater acidity is less favorable to lichen growth. Not only do lichens live on trees, but they can also be found on rocks, rusty metal, glass, cloth, plastic, bones, dead wood, and soil.
Lichens are considered beneficial in that their presence is an indication of atmospheric health. Their rhizomes do not penetrate or damage tree bark. Diseased trees may have lichens, but they are not the cause of the injury. Lichens are a food source for animals and are used as nesting material for birds. And, to me, lichen adds a touch of interest, in color, shape, and form to the park landscape.
For more information about lichen, see Rutgers Fact Sheet 1205: Tree-Dwelling Lichens
The Chrysler Herbarium of Rutgers University houses over 2,600 lichen specimens. Photos and information about them is available to the public, and can be accessed by clicking here.
