The neighboring plant eavesdrops on a nearby olfactory conversation, which gives it essential information to help protect itself. In nature, this olfactory signal persists for at least a few feet (different volatile signals, depending on their chemical properties, travel for shorter or much longer distances). For lima beans, which naturally enjoy crowding, this is more than enough to ensure that if one plant is in trouble, its neighbors will know about it.
Do Plants Smell?
Plants give off a literal bouquet of smells. Imagine the fragrance of roses when you walk on a garden path in the summertime, or of freshly cut grass in the late spring, or of jasmine blooming at night. Without looking, we know when fruit is ready to eat, and no visitor to a botanical garden can be oblivious to the offensive odor of the world’s largest (and smelliest) flower, the Amorphophallus titanum, better known as the corpse flower. (Luckily, it blooms only once every few years.)
Many of these aromas are used in complex communication between plants and animals. The smells induce different pollinators to visit flowers and seed spreaders to visit fruits, and as author Michael Pollan points out, these aromas can even seduce people to spread flowers all over the world. But plants don’t just give off odors; as we have seen, they undoubtedly smell other plants.
Plants obviously don’t have olfactory nerves that connect to a brain that interprets the signals. But Cuscuta, Heil’s plants and other flora throughout our natural world respond to pheromones, just as we do. Plants detect a volatile chemical in the air, and they convert this signal (albeit nerve-free) into a physiological response. Surely this could be considered olfaction.
This article was published in print as "What a Plant Smells."