Parmeliaceae

Usnea barbata

Old man’s beard · Beard lichen · Usnea

Untested Serious

Kingdom: Fungi — not a plant
Part used: whole
Native range: Temperate forest across the northern hemisphere, on tree bark
Morphology: A pale grey-green lichen hanging in fine branching strands from branches, with a distinctive elastic white central cord that can be seen by gently pulling a strand apart.

What is in it

lichen acids usnic acid

Evidence

Usnic acid has genuine antibacterial activity in the laboratory, particularly against Gram-positive organisms. No adequate clinical evidence for treating infection in people.

Safety

Usnic acid is hepatotoxic. Weight-loss supplements containing concentrated usnic acid caused a cluster of severe liver injuries in the United States, including cases requiring transplant and at least one death, leading the FDA to warn against the product LipoKinetix. Topical use is the traditional route and carries far less risk.

Interactions: Additive liver risk with hepatotoxic drugs

Regulatory: Concentrated usnic acid supplements have been the subject of FDA warnings. Topical preparations are permitted.

How the traditions classify it

Galenic Used in European practice for wounds and infection, and under the doctrine of signatures for the scalp, since it resembles hair.

Chinese Song luo — used for cough and for clearing heat.

Three systems, rating the same plant. Where they disagree, none of them is correcting the others — they are separate frameworks that arrived at their categories independently.

Historical use

Used as a wound dressing across Europe, Asia and North America, and as a battlefield dressing. The resemblance to hair produced a doctrine-of-signatures use for the scalp that has nothing to recommend it.

Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.

Worth knowing

Usnea is the pattern this collection keeps finding: a traditional topical use that is plausible, and a modern concentrated oral product that put people in liver units.

Usnic acid does kill Gram-positive bacteria, and a lichen wound dressing was not superstition. It is also a mitochondrial uncoupler — it makes cells burn energy without producing usable ATP, which is exactly why someone thought to sell it for weight loss, and exactly why it destroys livers. The same mechanism made dinitrophenol lethal in the 1930s.

Lichens grow extremely slowly, a few millimetres a year, and a beard hanging from a branch may be decades old. Commercial harvest of a slow-growing air-feeding organism is not a sustainable proposition at any scale.

Nomenclature verified against GBIF backbone taxonomy.