Plant Detective, The

Modern interest in mistletoe as a possible treatment for cancer began in the 1920s. For centuries, it had been used as something of a cure-all, but when mistletoe's immunostimulant properties were confirmed, the Druids' reverence for the healing power of this parasite got some scientific validation. Since then, lots of studies have been done in Germany, where many cancer patients augment conventional treatment with mistletoe extracts. In the lab, it kills certain cancer cells, while boosting the number and activity of white blood cells.

Mistletoe, a parasitic plant that grows on a wide range of host trees, shows up on every continent but Antarctica - and on each continent, it's been used in folk medicine. From ancient Greece into twentieth-century America, it was prescribed for epilepsy. Over the centuries, healers have used mistletoe to treat arthritis, menstrual problems, miscarriage (through controlling bleeding), hypertension, and pain - and that's just the short list. It's prescribed frequently in Europe. But don't try any of these uses without a trained health practitioner, because mistletoe can be toxic.

Passionflower is a beautiful climbing vine native to the Americas whose corona reminded people of the crown of thorns worn by Jesus during his crucifixion. It's a sedative, milder than valerian or kava - often, you'll find it used in combination with other calming herbs like lemon balm. Passionflower calms the nervous system, reduces anxiety, and soothes insomnia and muscle spasms. Scientists think it increases levels of gamma aminobutyric acid (GABA) in the brain. Don't use passionflower if you're pregnant or breastfeeding; it's a uterine stimulant that can over-sedate your baby.

The Efik people of the region that is now Nigeria used to force people accused of crimes to suffer a trial by ordeal: they'd be fed calabar beans, a known poison. If the accused died, they were judged guilty. If they lived, they were "proven" innocent. There's some pharmaceutical basis to this. It turns out that the poison of the calabar bean is absorbed in the mouth, where a guilty person might try to hold the beans, to avoid swallowing. For the guileless who swallowed them whole, the emetic properties of the beans might cause them to throw up the beans and escape poisoning.

You might have brushed by it in the forest, where this hairy-looking symbiosis between algea and fungi perches on tree limbs. The look of the lichen usnea explains its nicknames: "old man's beard," "tree's dandruff," "women's long hair," and "beard lichen." For centuries, it's been considered a handy medicinal. People grab some to dress wounds, or take it internally for infections or oral inflammation. But in the 1990s, when manufacturers of weight-loss drugs started adding sodium usniate (usnic acid) to their formulas, several cases of liver damage emerged.

It's not an old wive's tale: cranberry helps prevent and treat urinary tract infections. And it's not just the acidity: a compound in cranberries and blueberries keeps bacteria from sticking to bladder and urinary tract walls. Cranberries are high in several kinds of antioxidants, including proanthocyanidins, which give the ripe berries their vivid red color.

In the 1672 book New England Rarities Discovered, author John Josselyn described cranberries:

Among the artifacts discovered in the tomb of Egypt's Tutankhamen - objects meant to ease the boy king into the afterlife - were 3,000-year-old bulbs of garlic. Giving as well as receiving, Tut supplied daily rations of garlic to his pyramid-building slaves, for endurance and health. Garlic is a fabulous heart helper: its blood-thinning and anti-clotting abilities may slow down atherosclerosis and lower blood pressure.

Ever since nomadic tribes helped spread wild garlic from Central Asia to far-flung parts of the globe, garlic has helped humans fight microbes. Louis Pasteur recognized its antimicrobial power, as did doctors in WWI and WWII battlefield hospitals, where injured soldiers were given garlic to prevent infection and gangrene. Today's warnings of a "post-antibiotic" future mean garlic's power may turn out to be handy as drug-resistant bacteria become widespread.

In 1905, author Harriet Keeler wrote about the inner bark of the slippery elm tree: “It is thick, fragrant, mucilaginous, demulcent, and nutritious. The water in which the bark has been soaked is a grateful drink for one suffering from affections of the throat and lungs.”

Medicinal use of datura - also known as moonflower - is so ancient, no one is sure where the plant originated. Two important nervous system depressor drugs, atropine and scopolamine, are derived from it. Oracles in the Americas and Greece used it for divinations. Witches in medieval Europe applied it to their skin in ointments. And when modern-day researchers experimented (a risky proposition; one of the researchers died) with those old witches' recipes, they reported intense dreams of flying. Broomstick, anyone?