How Flowers Marvelously Evolved Resilience
Blossoms contort and twist back into optimal pollination position after getting bumped and battered
/https://tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/filer/c5/e7/c5e7e027-5cfc-4ea3-bd59-24229abc6196/2020_april16_triggerplant.jpg)
Plants and pollinators have evolved together to be specifically matched to each other’s needs. When Charles Darwin discovered an orchid with a nearly foot-deep well from its petals to its nectar, he theorized that there must be an insect to match. About 21 years later, the African hawkmoth was discovered with a foot-long, straw-like mouth called a proboscis. It wasn’t observed sipping from the orchid until 1992.
Coevolved pairs like these rely on each other. The animal gets food, and the plant gets pollinated. But many flowers, especially those with one line of symmetry like orchids, need to hold a particular position in order for pollinators to land safely. So, what happens if the flower gets knocked over? According to research published on April 6 in the journal New Phytologist, the fragile-looking plants bounce back, reorienting their blossoms back to the best pollinating position.
Certain flowers’ need for careful positioning is described in 200 years of botanical writing, ecologists Scott Armbruster and Nathan Muchhala write in their paper, but little attention has been paid to how flowers recover from accidents. What first caught Armbruster’s attention was a trigger plant, which normally stands vertically with flowers covering the stem facing outward, that had been knocked over by a fallen branch.
As Armbruster tells Brian Resnick at Vox, the plant didn’t give up—instead, Armbruster noticed, the healthy blossoms had begun to rotate back to their proper orientation, despite the state of their stem. The observation started a decade-long side project, artificially holding down the stems of 23 cultivated flower species from Australia, North America, South America and the United Kingdom, and tracking how the flowers recover.
"The common spotted orchid does it largely by just bending the main stem," Armbruster tells BBC News’s Matt McGrath. "It's pretty quick. Within a day or two, it's reoriented its main stem so that now all the flowers are in the right position.”
"The slightly more interesting ones were where each individual flower re-orients on its own, by the sub stem,” which branches off from the main stem to reach the blossom, Armbruster continues. “That's what you see with aconitum,” also known as wolf’s bane or monkshood.
The researchers tested three radially symmetrical flowers from Australia, called Clematis, Stackhousia, and Mandevilla, none of which reoriented to their original position when they were knocked over. But 95 percent of the bilaterally symmetrical flowers the ecologists studied were able to return to their original state, according to a statement.
To Vox, Armbruster clarifies that this doesn’t mean the flowers have “memory” of their initial state: “This is not fully known,” he says. Some plants also moved their leaves to better absorb sunlight.
“What I like most about this study is that they did very simple manipulations — just bending the flowers down,” Michigan State University evolutionary biologist Eric LoPresti, who was not involved in this study, tells Vox. “The simpler the manipulation is, the easier it is, often, to interpret.”