ADRIAN THOMAS / SCIENCE PHOTO LIBRARY ADRIAN THOMAS / SCIENCE PHOTO LIBRARY
Usnea florida lichen. Close-up of Usnea florida lichen growing on a tree. A lichen is a symbiotic organism comprising a fungus and an alga. The alga produces nutrients for the fungus by photosynthesis. Usnea florida is found on twigs and branches in the canopy of broad-leaved trees, especially oak. This lichen is a good indicator of air quality, as it is intolerant of high sulphur dioxide concentrations.
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