Beard lichen
Usnea spp.
Family · Parmeliaceae · Harmless
The grey-green beards hanging from branches in mountain woods. Not a plant and not a parasite: it is a lichen, and its presence says something very specific about the air there.
Where it grows
Uplands · Oak woods · Pine woods
Also known asold man's beard, usnea
In flower
How to tell it
Hanging, branched, grey-green filaments. The confirming test: pull a filament slowly and you see a white elastic cord inside, which no similar lichen has.
What it is confused with
No dangerous lookalikes known in the Iberian Peninsula.
What it is for
Its most valuable use is as an indicator: usnea is extremely sensitive to sulphur dioxide and disappears with air pollution. If it is there, the air in that valley is clean.