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Darwin orchids on display at World of Orchids

How Orchids Helped Charles Darwin Understand Nature—and How Darwin Helped Scientists Understand Orchids

Charles Darwin is known for his work in the Galapagos Islands, his study of birds and insects and the development of the theory of evolution as presented in his 1859 book On the Origin of Species. What is less well-known is Darwin’s work as a botanist and the important role that orchids played in the development of his ideas.

Darwin had an adventurous young adulthood; between 1831 and 1836 he sailed around the world as a naturalist on the HMS Beagle. But after he returned to the United Kingdom at age 27, chronic ill-health forced him to remain close to home.

But his studies continued. As well as drawing on his discoveries on the Beagle, he built greenhouses and gardens at his family home and used them as living laboratories for the study of evolution. He established relationships with botanists and naturalists around the world, and they frequently sent him seeds, cuttings and dried specimens of exotic plants.

Orchids were a favorite subject. Botanically speaking, orchids are members of the family Orchidaceae. This is one of the two largest families of flowering plants on the planet. Within the family, botanists have described about 28,000 species–more than twice the number of bird species on earth and about four times the number of mammal species.

Darwin studied both tropical orchids and those native to Britain. His work concentrated on one central question: How do the shapes, colors and scents of flowers contribute to their fertilization and, therefore, their success as a species?

An 1867 illustration by Thomas William Wood showing a moth pollinating A. sesquipedale. This was an imagined illustration of the process, drawn before the moth was discovered.

Darwin predicted that flower adaptations exist to promote cross pollination–that is, so that flowers are fertilized with pollen from other plants rather than with pollen they produce themselves. He painstakingly tested this hypothesis over a decade and found that self-pollinated plants are less healthy and more likely to be sterile. Cross-pollination results in stronger plants and, ultimately, the success of the species.

He summarized his work in an 1862 book with the snappy title On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing. The book served not only as a detailed botanical study but also as a rebuttal to critics of Origin of Species. Early readers of Origin of Species charged that it was too personal and not sufficiently scientifically stringent; in contrast, the Orchid book had enough rigor and detail to satisfy even the most demanding readers. Orchids also served to move the discourse away from debate over the origin of human beings and to less controversial territory where experts could find common ground.

In time Darwin’s work with orchids inspired naturalists in many areas of study. An article from Smithsonian describes the results:

Darwin’s explanation of curious floral forms as being the result of natural selection rather than the imaginative work of a divine creator enabled scientists to understand many previously incomprehensible phenomena. Vestigial organs, or organs that had become degraded and useless as species evolved, made sense for the first time. It didn’t seem logical that God would endow a flower with the shriveled, nonfunctional remains of a stamen, but it did make sense that a stamen no longer needed for effective reproduction would degrade over the course of many generations.

Xanthopan morganii praedicta with its long proboscis.

Darwin’s work with orchids also included an interesting prediction. In his 1862 book, Darwin described an orchid now known as Angraecum sesquipedale, which is endemic to Madagascar. A distinctive feature of the white, star-shaped flowers is a long green tube that emerges from the flower and holds nectar. This tube can reach between 10 and 17 inches long.

Darwin predicted that there must exist an insect with a very long proboscis–a sort of tongue–that could reach down the tube to drink the nectar within. In the process, the insect would pick up the flower’s sticky pollen, which it would then spread to other flowers. No such insect was known, and critics mocked the idea that Darwin’s theories could be used to posit the existence of living things.

However, in 1903, a large sphinx moth with a long, flexible proboscis was discovered in Madagascar. Named Xanthopan morganii praedicta, it has been observed fertilizing the orchid in the wild. Darwin was right, and one common name for Angraecum sesquipedale is Darwin’s orchid.

You can see Darwin’s orchid on display at World of Orchids through April 9. When you visit, check out the long, thin spur emerging from the flower and consider the leap of imagination and reason that gave Charles Darwin powerful insight into the natural world.

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