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."

4 Comments

1. 1. pebakke 01:09 PM 4/20/12

   This is awesome!!

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2. 2. pebakke 01:10 PM 4/20/12

   This is awesome!!

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3. 3. jvkohl 11:06 AM 4/21/12

   Re: "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."
   
   The concept of human pheromones has been challenged -- even by olfactory researchers like Richard L. Doty in his book "The Great Pheromone Myth." Cearly, however, the concept is one of olfactory/pheromonal communication that must occur for any species of plant or animal to survive. Nutrient chemicals, for example, calibrate invidual survival via their epigentic effects on intracellular signaling. The nutrients metabolize to pheromones that standardize and control reproduction.
   
   The common molecular mechanisms place the human pheromone-deniers in a catagory that could only be reserved for those who think that plant odors (as in food odors) do not have the same epigenetic effects on intracellular signaling as pheromones do in species from microbes to man. How (e.g.,on earth) could humans not produce and respond to pheromones. Are we evolutionarily adapted outliers due to random mutations, or is our behavior consistent with the epigenetic effects of nutrient chemicals and pheromones on pre-existing genetic variability across all species?

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4. 4. JamesDavis 04:55 PM 5/22/12

   Oh my God! I love this article. I have watched this plant my whole life and I could never find any information on it, so I always called it what my American Indian (Shawnee) mother called it - 'Love Tangle'. It always infested a weed (which is popular in South Central West Virginia), my brother and I called, 'Sword Weed'; strip the leaves off the Sword Weed (if you can withstand the pungent smell) and the stem is strong enough to use as a sword in play (I always won by brother in sward play because he was two-years younger than me.). We had tomatoes growing in a garden beside the Sword Weed and the Dodder always preferred the Sword Weed. The Sword Weed is a very pungent plant, more so than the tomato, but since the Sword Weed has no beneficial medical properties, we Indians had no interest in it. I have never seen the Dodder bloom because the Squirting Cucumber (Touch-Me-Not) always chocked it out and killed it before harvest, or blooming time.
   
   This is the best article I have read on SciAm. My complements to the author, Daniel Chamovitz.

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