Willow

Willow is the outstanding test case for whether pre-modern plant reasoning ever arrived at a real drug, and the answer is a qualified yes.

Willow bark contains salicin, a glycoside which the body converts to salicylic acid, an anti-inflammatory and antipyretic. The traditional use of willow bark against fever and pain therefore worked, in a modest way, for the reason the tradition could not have known. Salicin was isolated in 1828 and named for the genus Salix. Salicylic acid itself is harsh on the stomach; the acetylated derivative, acetylsalicylic acid, was developed at Bayer in the 1890s and marketed as aspirin from 1899. Meadowsweet, formerly Spiraea, contributed the spir in the name and contains related compounds.

The chain from willow bark to aspirin is real and is often told as a triumph of folk knowledge. Two qualifications are owed. First, the concentration of salicin in bark is low and variable, so the traditional decoction was a weak and unreliable version of what the isolated compound does. Second, the reasoning that led people to willow was not the reasoning that turned out to be right.

That second point deserves the emphasis. The stated Renaissance ground for using willow against fevers and agues was that the tree grows in wet, cold places and so must counter hot, wet conditions, a doctrine-of-signatures argument about habitat. It is a false theory. It happened to point at a tree that contained an analgesic. One success across a very large number of attempts is what chance looks like, and it is not evidence for the method.

Culpeper places willow under the Moon, and gives two grounds: the tree's affinity for water, which is the Moon's element in the elemental scheme, and its cooling action. In his system that is a coherent argument, and it is the argument, not an observation.

The wider symbolic load on the willow is older than the herbal and largely independent of it. The tree is the standing emblem of grief and of forsaken love in English usage, the green willow garland worn by the jilted, Desdemona's willow song in Othello, the willow of the Psalm 137 exile, though the tree in that verse is more probably a poplar. Its weeping habit is the obvious source, and the weeping form most familiar in Europe, Salix babylonica, is in fact an East Asian species carried west along the trade routes and given a Babylonian name by Linnaeus on the strength of the Psalm. The name is a mistake preserved in the botanical record.

Willow is also genuinely useful in ways that have nothing to do with symbolism. It coppices readily, roots from a cut stake pushed into wet ground, and yields the withies for basketry, hurdles and creels; it is planted to stabilise riverbanks; and it is the timber of cricket bats, from a particular cultivated variety. The association with water-divining rods is real as folk practice and the practice does not work under controlled test, which has been examined repeatedly.

The ease of rooting deserves emphasis, because it probably underlies the symbolism rather than the other way round. A willow stake driven into wet ground will grow. Cut a willow hard and it responds by growing more vigorously. A tree that cannot be killed by cutting, and that reproduces from its own severed parts, is a natural emblem of grief that persists and of life continuing after loss: and pollarded willows, cut back repeatedly to the same knuckled head, are among the most characteristic and most obviously artificial features of the northern European landscape.