Usnea is a type of lichen that grows on trees and rocks, often found in cool, moist environments. It has a distinctive appearance, resembling long, grayish-green strands that hang down like hair. This lichen is sensitive to air pollution, making it a useful indicator of environmental health. Usnea is also known for its medicinal properties. Traditionally, it has been used in herbal medicine to treat infections and boost the immune system. Its antibacterial and antifungal qualities are attributed to compounds like usnic acid, which researchers continue to study for potential health benefits.