Q: I’m finding circular white spots on the trunks of my trees and palms. What is it and will it kill my plants?
M.L., via email
A: What you are seeing are organisms called lichen, and they don’t harm plants.
Lichen (pronounced “liken”) is a biological class of complex organisms (a fungus and alga or cyanobacterium) that have a symbiotic relationship. The green algae and cyanobacteria produce food by photosynthesis. The fungi cannot photosynthesize, but provide a protective exterior surface for the algae/cyanobacteria. This enables the algae/cyanobacteria to exist in full sun, thus maximizing its ability to produce food for both. Lichen gain water and mineral nutrients mainly from the atmosphere, through rain and dust.
Lichen not only grow on plants but on the ground and on rocks. Lichens have a great deal of variability in color and form depending on the species. The color can range from white to green to yellow/orange/red, and some have black specks. Some are flat and others look like ruffles. Some look like small, leafless shrubs.
Sometimes seeing a large amount of lichen indicates that there is branch die-back and more light is reaching the trunk or limbs. The die-back can be caused by a root problem, but the lichen is not the culprit. Another reason for lichen to be more prominent is during natural leaf drop in deciduous plants. More light is reaching the lichen or there are fewer leaves to obstruct your view of these interesting organisms.
Lichens indicate the air quality is good because they are sensitive to air pollution, some species more so than others.
To give you an idea of how diverse lichens are in South Florida, Everglades National Park conducted a lichen project identified more than 400 species. Based on this research, Everglades National Park ranks fifth in lichen diversity compared to other natural areas in the United States.