The willow tree grows primarily in central and southern Europe, although it is also found in North America.
The bark is used to make herbal extracts.
Willow bark was used traditionally by herbalists for fever, headache, pain, and rheumatic complaints.
In the late 19th century, the constituent salicylic acid was isolated from willow bark and went on to become the model for the development of aspirin (acetylsalicylic acid).
1 Fluid oz.