Usnea, also known as Old Man’s Beard and Woman's Long Hair, is a type of lichen that grows on trees. Specifically, it’s an example of a symbiotic relationship between a fungus and an algae.
Usnea is considered an herb because it has several practical uses, evidenced by its use for more than 1,500 years. The whole specimen, which is high in vitamin C and other antioxidants, is typically used to make tinctures and extracts for cosmetic use. Usnea lichen is also a common ingredient is natural deodorants.