Willow (Salix vitellina, usually Salix alba var. vitellina)
Willow, the remedy for those filled with self-pity and resentment, is made by the boiling method. Salix vitellina, or golden willow, is considered to be a variety of white willow, Salix alba.
Used historically to treat pain and fevers, the modern-day use of compounds related to those in willow bark is due to the work of Rev. Edward Stone. He was suffering from agues (a collection of symptoms including intermittent fever) and decided to try chewing a piece of willow bark. He felt it helped his symptoms and, after testing the powdered bark on 50 of his friends, reported its benefits in a letter in 1763.
The bark contains the compound salicin which is readily oxidised to give salicylates (ions of salicylic acid). In the tree these act as allelopathic compounds, excreted into the soil to deter other plants from growing. In the human body they act as COX enzyme inhibitors so reduce the production of prostaglandins. These would cause pain and inflammation.
However, the use of salicylates can cause the side-effect of stomach bleeding so in 1890, the pharmaceutical company Bayer launched a project to look for a gentler alternative – one which retained the beneficial properties but with reduced potential side-effects. The compound they came up with was acetyl salicylic acid, better known today as aspirin.
Aspirin was the first of a new class of drugs known as Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) and became widely used. It was the drug of choice against the Spanish flu pandemic of 1918. The use of aspirin to treat inflammation and fevers has been overtaken by newer drugs such as paracetamol. However, the potential side-effect of stomach bleeding has led to another use. Today many people take a low dose of aspirin to help prevent heart attacks and strokes. Aspirin remains one of the most important and widely used drugs on the market with an annual global usage of over 100 billion tablets.
Willow bark is still used by herbalists to treat pain, inflammation and fevers. Other chemicals present in the bark, such as flavonoids, may contribute to its success at lower doses than aspirin. These may also reduce the occurrence of side-effects.
Willow has many other traditional medicinal uses. Culpeper recommended using a drink made by mixing the boiled leaves or seeds in wine to extinguish the heat of lust in both men and women! Galen describes using the burnt ashes of the bark, mixed with vinegar to take away warts, corns and superfluous flesh. Today, salicylic acid (the parent salicylate) is used to treat warts, corns and verrucae.
In the 1960s, millions of willow and poplar trees were planted in Beijing. However, these shed catkins in the spring and this can be a fire hazard. The fluff can also cause irritation to the respiratory system. Reducing the number of female trees, the main culprits, would be beneficial and recently, only male trees have been planted. For existing female trees, two possible solutions have been tried.
The trees can be given a ‘sex-change’ – their upper branches are removed and male branches grafted on, but, although effective, this is time-consuming and expensive.
In 2016, a chemical method was attempted. 15,000 trees were injected with three plant chemicals which are growth promoters, including indole-3-butyric acid (IBA). These compounds inhibit flowering and promote vegetative growth – which doesn’t require catkins to be produced. The injections are about 10 times cheaper than the ‘sex change surgery’. IBA is an auxin, which occurs naturally in willows and is used in some commercial plant rooting products. Results of this trial have not yet been publicised.