In the nineteenth century, many wealthy English people became obsessed with orchids. They financed secretive expeditions to far-off lands in which professional collectors scoured jungles for rare orchids. Newly discovered species were sold at auction in London for exorbitant prices. The craze grew so fervid that it became known as orchidelirium.
While this fever consumed rich Victorians, a leading English naturalist began to study the flowers, and the methods by which they were pollinated by insects. In 1862, he proposed a theory of coevolution in his book Fertilisation of Orchids, using the example of an unusual Madagascar orchid to argue that insects and flowers might affect each other’s evolution by developing extreme specialization. That orchid is now commonly known as Darwin’s orchid, after the naturalist: Charles Darwin.
“Darwin was very much involved in orchid research, he found them fascinating,” says Wade Wheatley, an assistant horticulturist for the greenhouses at the Chicago Botanic Garden, which holds an annual orchid show in late winter that featured approximately 10,000 plants this year. “Darwin’s orchid and its pollination by giant sphinx moths is a classic example of how orchids get specialized into niche habitats. That’s why there aren’t a million of that type of orchid: there aren’t that many giant sphinx moths to pollinate them.”
Depending on whom you ask, the orchid family is the largest or second-largest plant family in the world, with some 28,000 different species. They make up approximately one-seventh of all described plant species, according to Wheatley, and can be found on every continent but Antarctica. But despite the huge variety of types, there are relatively few plants within each species. “There aren’t hundreds of thousands of plants in these species,” Wheatley explains. “It’s fairly limited.”
This scarcity arises from the very same specialization that Darwin used orchids to study. “Orchids are most diverse in the tropics, where there’s a lot of evolutionary pressure,” Wheatley explains. “Resources are very limited, but conditions are good for growth year-round. So, basically, plants will grow to fill any niche that’s available to them. They get pushed to more and more extreme forms to fit more and more extreme niches in the environment, but these are not large niches. They can’t support a tremendous number of plants. That’s why there are both so many different types of species and so few plants within them.”
In filling these niches and in their incredible variety, orchids have devised unusual forms of pollination, several of which are explored in the two-part series Plants Behaving Badly. “Just about every pollination technique occurs within the orchid family, with the exception of wind dispersal,” Wheatley says.
There’s pseudo-copulation, where the flower mimics the appearance of a female insect and is pollinated when a male insect attempts to mate with it. Pseudo-antagonism involves an imitation of an aggressive insect in order to goad another insect of that species to attack it, pollinating it in the process. Cleistogamist orchids pollinate themselves without ever opening their flower bud: “It’s a risky technique because it reduces genetic variability in the offspring,” Wheatley says, “but it leads to a ton of offspring, because the orchid isn’t depending on outside forces.”
Collectors have also taken it upon themselves to introduce genetic variation, by mutating, cross-breeding, and cloning orchids to create unique and rare hybrids. This ability to play God, coupled with the draw of the exoticism of the tropics, is part of what attracted the Victorians. “Once you discover that you can cross two different species to get different plants, or that you can grow a hundred of one species and maybe two or three of them will be larger or more colorful than the rest, then you can start a breeding program to improve upon nature, which is another passion of the Victorians,” Wheatley says. “They believed that they could do nature better than Nature could.”
Add in the rarity of many species and the common perception that orchids are difficult to grow, and the drive with which people pursue orchids is easily understood. As Susan Orlean wrote in a 1995 New Yorker article that later became the book The Orchid Thief, which in turn provided the basis for the Spike Jonze-directed film Adaptation, “The botanical complexity of orchids and their mutability makes them perhaps the most compelling and maddening of all collectible living things… To desire orchids is to have a desire that can never be fully requited.”
Succinctly put by Orlean, “Orchids seem to drive people crazy.”