Curiosities: Why do flowers smell, and why do plants smell, too?

July 24, 2007

The luscious aroma of flowers attracts lovers, and the biological role of that smell is similar: to attract pollinators. “Plants need to attract insects, bats and hummingbirds to transfer the pollen and create fertile seeds,” says Hugh Iltis, professor emeritus of botany at UW–Madison.

Pollination is the transfer of pollen (the plant equivalent of sperm) to eggs. Some plants rely on wind or gravity, but many require animals to do the transportation. The smell of the flower alerts pollinators that the plant is ready to be pollinated, and when the animals arrive to collect pollen and/or nectar, pollen gets transferred.

Plants and pollinators often display a long history of mutual evolution, Iltis adds. When Charles Darwin saw a flower with a foot-long tube during the 1800s, he predicted the existence of a moth with an equally long “tongue” that could reach the female parts at the bottom of the tube. This moth was discovered more than a century later!

The minty, oily or sharp smells produced when you crush a leaf or stem play a defensive role, Iltis says. These smells come from chemicals that are often toxic to animals, and thus serve as a one-two punch: they smell (and taste) terrible, and then they make you sick if you ignore your senses and take a bite.

During the long struggle for existence, Iltis says, evolution has shaped every part of plants – including their chemical composition. But pollination is a troublesome subject: many crops are under threat as honeybees succumb to “colony collapse disorder.” Although the cause is unknown, environmental disturbance likely plays a role, Iltis says.