Did This Plant Evolve to Look Like a Bunch of Hummingbirds?

In nature, mimicry is often more than just flattery: Everything from baby birds to caterpillars use this strategy to avoid being bugged or eaten. But is that the case with a flower whose uncanny resemblance to a hummingbird could be more of an optical illusion than evolution?

The question stems from a viral Reddit thread started a few weeks back when a user posted a photo of the delicate green blooms of Crotalaria cunninghamii, a member of the legume family that grows in Central and Western Australia. Some commenters attributed the flowers’ form, which looks bizarrely close to a feeding hummingbird, to Batesian mimicry, a tactic some animals and plants use to trick predators into thinking they’re dangerous or otherwise disgusting to bite into; others pointed to simulacrum, a psychological phenomenon that causes humans to see superficial likenesses. A few armchair plant experts also chimed in, claiming the similarity was simply a coincidence and that the shape was an adaption to attract certain insects and pollinators. 

Michael Whitehead, a plant ecologist based at the University of Melbourne, added his own ideas to the thread, which accumulated hundreds of posts and more than 48,000 votes. Ultimately, he realized that there’s little research on Crotolaria and its capabilities. “I've been interested in this species for some time; the unusual color brought it to my attention,” he told Audubon over email. “Its core habitat is in quite remote deserts, so there's very little published work on it. [What we know is that] it has features consistent with bird pollination: large flowers with a long keel on the petals.”

On Reddit, Whitehead also shared a photo of Crotalaria cunninghamii from an angle where the hummingbird resemblance is harder to see. He then linked to a 2016 paper published in Austral Ecology where researchers concluded that the species' pollination traits favor birds like honeyeaters, as well as rodents. This, along with the important fact that there are no hummingbirds in Australia, adds further support to the adaptation angle.

Carlos Magdalena, a science and horticultural researcher at Royal Botanic Gardens, Kew, better known as “the Plant Messiah,” agrees that the flower’s contours are serendipitous. 

“It has one of the typical shapes of its family, but in this case, the proportions makes it look like a bird,” Magdalena says. “There are more than 500 species of Crotalaria around the world, and they can have flowers of many different kinds.”

Another flower that shares a resemblance to a bird, Magdalenena adds, is Pecteilis radiata, an orchid that looks like an egret taking flight. The plant is found in the wild in China, Japan, Korea, and Russia.

Crotalaria cunninghamii is named after Australian botanist Allan Cunningham, who was the first to describe it for science between 1816 and 1839. Its sap has reportedly been used by Aborigines to treat eye infections, showing that these flowers might hold other surprises for nature nerds in the field and on the internet.