Have you ever heard of a plant that’s not really a plant at all?
Usnea, also known as Old Man’s Beard, is a lichen that grows on trees in temperate and humid climates worldwide. It has a distinctive appearance, resembling thin, grayish-green strands or tufts hanging from tree branches.
So, what makes this strange-looking organism so special?
1. A Unique Symbiotic Relationship
Usnea may look like a single plant, but it’s actually a lichen – a symbiotic relationship between an alga and a fungus. The fungus provides structure and protection, while the alga produces nutrients to sustain them both.
STOP BUYING GREENS: This Machine Grows $1000s Worth Automatically
✓ Set It & Forget It: Fully Automated Growing
✓ From Seed to Harvest in Days - No Experience Needed
✓ Grow Premium Microgreens Worth $50/lb Year-Round
Note: This is an affiliate link and we may earn a small commission if you purchase at no additional cost. This helps keep our website free to use.
Lichens are estimated to cover approximately 8% of the Earth’s land surface, with over 28,000 species worldwide. Usnea belongs to the Parmeliaceae family, the largest family of lichen-forming ascomycetes.
2. Centuries of Medicinal Use
Usnea has been used in traditional medicine for centuries. The ancient Greek physician Hippocrates allegedly used it to treat urinary ailments, while it’s regarded as a treatment for wounds and inflammation in South African folk medicine.
Native American cultures have used Usnea to treat lungs, intestines, throat, sinuses, and the urinary and reproductive system.
The Dakota people call Usnea “Chan wiziye,” which translates to “on the north side of the tree” or “spirit of the north wind,” considering it a sacred herb. Its long history of use spans cultures and continents, hinting at its potential medicinal properties.
3. Packed with Powerful Compounds
Usnic acid and polyphenols, the main active compounds in Usnea, are thought to provide most of its purported benefits. Usnic acid, responsible for Usnea’s pale greenish color, has been shown to exhibit multiple antibiotic and analgesic properties.
Other compounds like depsides, depidones, and benzofurans may also have health effects, but more research is needed. These unique compounds are rarely found in other organisms, making Usnea a valuable source of potential medicinal agents.
4. Potential Wound Healing Properties
Research in rats (ref) shows that Usnic acid increases markers of wound healing, such as collagen formation, when applied directly to wounds.
There’s also evidence that Usnic acid may protect against Staphylococcus aureus bacteria, which are often responsible for skin infections. While more research is needed, Usnea’s potential to promote wound healing is promising.
5. Sensitive to Air Pollution
Usnea is very sensitive to air pollution, especially sulfur dioxide. Under poor growing conditions, such as areas high in pollution, Usnea may grow no larger than a few millimeters, if it survives at all. Where the air is unpolluted, Usnea can grow to 4-8 inches long.
This sensitivity to air pollution makes usnea a valuable bioindicator, as it tends to only grow in regions where the air is clean and of high quality. The presence of healthy usnea growth can be a sign of a thriving, unpolluted ecosystem.
6. Beyond Medicine: Multiple Uses
Usnea has found its way into various applications beyond traditional medicine. It’s been used in cosmetic production for its antimicrobial and antifungal properties as a preservative and deodorant. When dry, Usnea lichens are flammable and can be used as a fire starter.
During times of scarcity, some Usnea species have even been used as food sources. For example, people in Bosnia and Herzegovina ate Usnea barbata during the Bosnian War, particularly in the winter when other plant material was not readily available.
7. Vital Role in Forest Ecology
Lichens like Usnea play crucial roles in forest ecology. They appear as primary colonizers in forest areas after a fire and carry out nitrogen fixation, enriching the soil for other plants to grow.
Usnea also provides nesting material for some bird species, like the northern parula warbler.
However, where Usnea has declined due to air pollution, the northern parula has also vanished as a breeding species. This highlights the interconnectedness of ecosystems and the importance of preserving sensitive species like Usnea.
8. Threatened by Overharvesting & Habitat Loss
Many Usnea species have become rare due to their long history of use and sensitivity to air pollution. In North America, Usnea lichens are threatened by habitat loss. It’s important that Usnea collection for research and other harvesting be conducted in a sustainable and ethical manner.
It’s illegal to collect Usnea in national parks (ref), and only limited lichen collection is allowed on public lands like the Nantahala and Pisgah national forests. Where collection is allowed, sustainable harvesting practices should be observed, such as collecting fallen branches covered in Usnea or detached Usnea from its substrate, rather than harvesting directly off trees.
9. Identification Can Be Challenging
With over 350 Usnea species identified worldwide, only a relatively small number have the pendant, filamentous morphology of beard lichens. Common beard lichen species in North America include U. cavernosa, U. longissima, U. strigosa, and U. trichodea.
However, certain lichens belonging to other genera, like Alectoria sarmentosa (Witch’s hair lichen), can be mistaken for Usnea due to similar external morphology. Unlike Usnea, Alectoria lichens do not have a flexible string-like central core within the pendant lichen thallus.
Proper identification is crucial for those interested in harvesting or studying Usnea.
Nancy has been a plant person from an early age. That interest blossomed into a bachelor’s in biology from Elmira College and a master’s degree in horticulture and communications from the University of Kentucky. Nancy worked in plant taxonomy at the University of Florida and the L. H. Bailey Hortorium at Cornell University, and wrote and edited gardening books at Rodale Press in Emmaus, PA. Her interests are plant identification, gardening, hiking, and reading.