Medicinal Uses of Usnea, Old Man’s Beard. There are hundreds of species of Usnea, which grows world-wide and is found on every continent. Usnea barbata is one of the species commonly … Usnea, pronounced ooze-nee-ah and better known as old man’s beard, is the long, lacy, greenish lichen that grows from tree trunks and branches in forests across New Hampshire and … More Medicinal Weeds. by tree pony. Usnea barbata Common name: Old Man’s Beard, Tree lichen Family: Usneaceae Part used: Whole lichen (dried thallus) Constituents: Lichen acids (usnic acid and derivatives, diffractaic acid), … In a previous article we shared the anti-microbial properties of medicinal weeds – Farmer’s Friends (), and Sida ().Another broad acting anti-microbial ‘weed’ commonly found in this area is the Old Man’s Beard …