Lichens are often blamed for killing a tree or shrub but this is not true. This content printed from the website located at: This website would like to use cookies to collect information to improve your browsing experience. While the tree’s leaves may shade the available sunlight for the lichens during the warm weather growing season, the lichens do not similarly affect the leaves. Algae, lichens and moss often form green or grey, powdery or mossy, crusty growths on the stems, branches and trunks of trees and shrubs. (Photo by Nick Polanin.). The fungal filaments make up about 80% of the lichen body. They grow on healthy trees, as well as stressed or otherwise unhealthy ones. Different lichen species can grow on many types of surfaces, including tree bark, dead wood, bare rock, cleared soil, rusty metal, animal bones, glass, plastic and cloth. Together they thrive in some of the harshest environments on earth where few other plants and neither partner alone can survive. Abundance lichen presence concentrated on damaged or dead wood may be a warning of present or impending invasive disease or decay caused by fungi, bacteria, viruses or insects and may require corrective action by homeowners or tree care professionals. Their rhizines typically do not penetrate deep enough into the inner bark, and cause no harm to the trees they inhabit. A lichen may form if spores of the fungal component germinate near compatible algae. They are most numerous on limbs and trunks of large mature trees and shrubs in full sun, particularly those plants with badly thinned canopies. Strigula spp. It is the primary reference for lichen identification and related information in this fact sheet. Many species of birds use lichen materials in constructing their nests. with Rutgers websites to: or complete the Report Accessibility Barrier or Provide Feedback Form. Lichens are numerous and important organisms in the natural environment that are generally beneficial in nature. The three types of lichens are (1) crustose forms, which are flattened against the limb (figure 1); (2) folicose forms, which produce leaflike folds above the limb (figure 2); and (3) fruiticose lichens, which produce highly branched structures with hair or fingerlike projections (figure 3). No pesticides are currently registered for the control of lichens commonly found on the twigs and branches of shrubs and trees. The musicocolous lichens grow on live moss, and the foliicolous lichens prefer evergreen leaves. Since the fungus cannot produce its own food, it is dependent upon another life form to provide that essential function. The numerous species of shield lichens are one of the many glories of lichenology in the Southeast. Lichen species on bark do not follow the classic succession of crustose followed by foliose and then fruticose that is evident in the colonization of rock. Lichen sexual reproduction is quite complicated as two or more organisms are contained in the lichen. The growth of lichen on tree bark depends more on the physical surface of the bark than on the kind of trees. Many lichens are more evident on stressed or old tree trunks and branches giving the appearance of a "cause and effect" association with disease and decay. Lichen species are so numerous and diverse that there are individual exceptions to most general statements about them. Few lichens are found in areas with high levels of ozone, sulfur dioxide, acid rain, and other common air pollutants. Lichens also can be somewhat differentiated by the specific type of habitat where they live, such as rock, soil or trees, as well as their geographic distribution. Main photo (l-r): Lichens on tree trunk; Lichen and moss on oak bark; Foliose lichen on crabapple tree branch (Photos by George H. Individuals with disabilities are The presence of lichens on healthy trees should be welcomed as likely positive indicators of lower levels of air pollution and a reasonably good quality of atmospheric conditions in the neighborhood. The three main body groupings are crustose (crust-like,), foliose (leaf-like, seen above), and fruticose (tube or beard-like strands). As bark ages, it changes in chemistry, texture, and ability to retain water, thereby influencing the type of lichen capable of living there. While they grow very slowly, i.e. These often inconspicuous, hardy, and adaptive plantlike organisms are composed of two fungi and a green alga. The lichens are not the cause for the condition of the stressed tree. Most lichen species grow best where there is sufficient light and moisture within a moderate temperature zone. Heavy infestations of lichens are most common on shrubs and trees in declining or poor health due to other factors. ALABAMA READY - Resources for Dealing with Hurricanes, Planting and Establishing Woody Landscape Plants, Lichens on Woody Trees and Shrubs, ANR-0857, Alabama Lichen identification most often is determined by the descriptive appearance, size, shape and color of the lichen body and the reproductive characteristics. Lichens may reproduce in a sexual, asexual, or vegetative manner. Tree lichens appear on many trees. Cooperative Extension System. Groerig, David J., Jim A. Chatfield, Sarah D. Ellis, Dr. Landon H. Rhodes, and Dr. Michael J. Boehm, (2009) "Lichens." The various chemicals produced by lichens are also identifying markers. Following recommended establishment, watering, and fertility practices will promote the development of a thick leaf canopy, which will inhibit lichen growth on twigs and limbs. So, no need to worry about lichen harming your tree, but you should reach out to a professional arborist if you have other concerns about tree health. The bark of a healthy tree continues to expand and slough off with the growth of the tree. Lichens are beautiful, especially when you view a lichen-drenched Douglas-fir or a colorful crust-covered cliff, and up close when viewed under a hand-lens or microscope. For more information, contact your county Extension office. School of Environmental and Biological Sciences, New Jersey Agricultural Experiment Station, Office of Continuing Professional Education, Tree, Shrub, and Flower Growing Publications,, Report Accessibility Barrier or Provide Feedback Form, Rutgers, The State University of New Jersey, Executive Dean of Agriculture and Natural Resources, George H. Daniel, Rutgers Master Gardener, Somerset County, Nicholas Polanin, Agriculture and Natural Resources Agent, Somerset County.