This is a frequent question we get at the plant clinic. Many residents complain of “spots” or a “strange disease” growing on their trees, especially on palms. But this is not a disease, it is in fact Lichen.

Lichen Biology

Lichen are an association between two organisms, a fungus (usually ascomycetes) and a photosynthetic algae or cyanobacteria. The fungus provides the house, while the photosynthetic partner provides the food. Lichen occur in a variety of shapes, forms, and colors. They are also found globally in diverse climates. In ecology, lichen are important as pioneer species as they are the first to colonize bare rock and start paving the way for ecosystem succession. In the wild, some animals use lichen as a food source and birds use them for making their nests.

Lichen in our neighborhoods

In our neighborhoods, lichen can be observed growing on tree trunks and branches sometimes resembling moss. They thrive on light and moisture and tend to be sensitive to pollutants. Thus, the presence of lichen tends to be an indicator of good air quality. Lichen are not pathogenic (disease causing) and do not require any treatment or removal from your trees. Next time you see these “spots” on your tree, appreciate them for their uniqueness, beauty, shape and color.

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