Living with lichens

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.        

Among our recent “Whatzat?” questions, is a grayish or greenish growth that forms on the trunks and stems of trees. (Lichen photo 1). These growths are lichens. Lichens are actually two organisms; a fungus and an algae that form a symbiotic relationship and function very much like one organism. A common question about lichens is “Do they harm trees?” The answer is no. The algae part of the lichen is photosynthetic, and therefore they are able to produce their own energy and do not take any resources away from the tree. In fact, lichens often grow on non-living substrates such as wood, concrete, tombstones, benches and so on (Lichen photo 2). If a homeowner observes a dead tree or dead branch covered with lichens on it, this is a coincidence; the lichens did not cause the branch or the tree to fail. The tree trunk or branch simply provides a porous surface for the lichen to attach. Lichens are often fairly inconspicuous, but in some moist areas, such as the Pacific Northwest, they may form a mat that completely coats branches.

Fast facts about lichens

  • Lichens grow in some of the most inhospitable places on earth from deserts to tundras.
  • Lichens are commonly grayish-green, but may also be yellow or red, depending of the type of algae associated with the fungus.
  • Lichens are sensitive to air pollution, and researchers are investigating their use as a bio-indicator of air pollutants such as sulfur dioxide and ozone.

Lichens are fascinating organisms, if you are taking a liking to lichens try these websites:

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