The staples of many a Christmas celebration include fruitcake, eggnog, reindeer sweaters, and, of course, mistletoe. One sprig of mistletoe in a doorway can spark instant holiday romance. Long before this seasonal plant became associated with kissable moments at holiday parties, mistletoe was sought after for its purported magical powers and medicinal properties.

Mistletoe is a semiparasitic plant, meaning it feeds off another organism while growing. Mistletoe seems to sprout from nowhere because its seeds stick to birds’ beaks, hitchhiking rides to the trunk of whatever tree the birds should visit. The seeds then expand their roots into the tree’s bark to absorb key nutrients. Although mistletoe may be poisonous to humans, it is benef...