Sliding down a steep creek side somewhere in western Maryland, a group of botanists and ecologists are on the hunt. It’s a cloudy day in May 2018, and they’re searching for an elusive orchid called the white lady’s slipper, or Cypripedium candidum.
The members of the group have turned off the GPS functions on their phones to keep their location secret. This plant is literally off the map—not only because it is rare but also because it is highly sought after by collectors.
The white lady’s slipper is named for its fragile flowers, which vaguely resemble tiny moccasins and have a sweet smell. Much of the orchid’s native habitat has been paved over, but it grows freely somewhere in this lush landscape—
a preserve owned by The Nature Conservancy.
Orchids can be fickle and fascinating plants, and scientists are really only beginning to understand them. Some remain dormant underground for years, presumed dead by those looking for them. Some bloom for only one day each year. And all germinate from seeds as small as dust. Many questions surrounding these plants—including how they’ll fare in a changing climate—remain unanswered.
On the preserve in Maryland, Deborah Landau, an ecologist for TNC, leads the crew that includes Dennis Whigham, a botanist at the Smithsonian Environmental Research Center, down a muddy bank before climbing nimbly up another ridge. Whigham is no stranger to getting his hands dirty in the field. He has devoted much of his life to studying orchids around the world, tracking them down where they thrive in hard-to-get-to habitats like steamy jungles, swamps and bogs, often tucked into the branches of tall mature trees.
With an estimate of at least 25,000 species in existence, and new species being discovered regularly, orchids are believed to be the world’s most diverse family of flowering
plants. They outnumber all mammals, reptiles and birds combined. And scientists estimate that they account for about 10% of all flowering plant life on Earth.
But that impressive quantity and diversity have made ensuring their future a costly challenge. Of the 200-odd species of orchids native to North America, more than half are threatened or endangered in some part of their range.
Several research endeavors have cropped up in the United States to better understand North America’s orchids—the largest among them a nationwide collaboration led by Whigham. To build a unified bank of research, he launched a joint effort in 2012 between the Smithsonian Institution and the United States Botanic Garden called the North American Orchid Conservation Center. The center is working with more than 50 groups and dozens of volunteers to collect samples of every native orchid species in the U.S. and Canada. Each sample gives researchers a chance to better understand how the plants germinate and reproduce.
On this overcast spring day, the orchid hunters are moving one step closer to solving these biological mysteries. Past an exposure of bedrock, beneath a tangle of brush on the cliff side above them, they find what they’ve been looking for: the delicate blossoms of the Cypripedium candidum.
“There’s so little known about many orchids,” says Whigham. “Very few of them have been studied in detail by anybody.” The center aims to address that research gap and in the process help scientists—who are going to some extreme lengths to study this enigmatic plant family—conserve and restore orchid populations across North America.
Orchids begin life as seeds so minute they can only be seen under a microscope. They do not contain any stored food to fuel their growth. Instead, when seeds land in soil or on trees, they rely on a suite of host fungi nearby to supply the nutrients and other resources they require.
“You’re never going to see this fungus unless you’re looking at the [orchid] roots or you’re looking into soil with a microscope,” says Melissa McCormick, a research scientist at the Smithsonian Environmental Research Center in Edgewater, Maryland, who collaborates with Whigham. “That has meant that these orchids and these fungi are very poorly studied and not a lot has been known about them.”
That’s changing, though, as volunteers collect seeds, segments of the plant’s roots and a single leaf from native orchids and send them to the North American Orchid Conservation Center. The leaf tissue, stored in little coin envelopes, goes into a genetic bank for DNA research into the plants. Fungi are extracted from the plant roots. The lab grows the fungus in petri dishes, sequences its DNA and stores it long-term in test tubes.
Quote: Dennis Whigham
The result is a growing body of samples from across the United States and Canada—enough to help researchers study these complex interrelationships in new ways and learn how to propagate orchids with help from their symbiotic fungi.
That research has become even more important as orchids face increasing threats. Habitat loss, poaching, and deer foraging have reduced orchid numbers. Some species, Whigham says, could become viewable only in botanic gardens, like endangered animals found mostly in zoos.
Even less studied is how a changing climate will affect these plants. Wetter or drier weather could hurt the fungus in the soil, Whigham says, which could alter an orchid’s ability to germinate. Changes in seasonality, or phenology, could hinder the plants’ ability to reproduce.
The Science of Seduction
Many orchids achieve reproduction by rewarding thirsty pollinators with nectar in return for their pollen-delivery services. But about one-third of orchids use deceptive strategies to coax insects or small birds to their flower. This trickery can take many forms.
The spider orchid (Brassia caudata), with its long, limb-like petals and sepals, masquerades as the prey of female spider-hunter wasps, inducing the insects to grasp and then sting the spider-shaped flower. Before a fruitless attempt at predation is complete, the wasp bumps into a package of pollen that clings to its head.
Some orchids, such as the stream orchid (Epipactis gigantea), use a technique called “brood-site imitation” to trick flies into laying their eggs inside the flower. The stream orchid produces a scent that mimics the smell of honeydew, a liquid produced by aphids. Some flies lay their eggs near aphid nests to give their young a ready meal when they hatch. In this case, the back of the bamboozled fly skims off some pollen from inside the flower as the insect exits the flower.
In another strategy called “food deception,” the pink lady’s slipper (Cypripedium acaule, seen here) lures a bee to a slit in its flower pouch by excreting a sweet smell. To escape the pouch, the bee must pass under the stigma, a floral reproductive organ, and then squeeze through one of two openings—each with a cache of pollen above it that hitches onto the bee’s body as it makes its escape.
One study of the early spider orchid (Ophrys sphegodes) found that warm spring temperatures can disrupt the plant-pollinator relationship. The early spider orchid lures young male bees to its flowers by emitting a scent that mimics the sex pheromone of female bees. To avoid competing with female bees for the males’ attention, the flower needs to bloom after male bees emerge from winter hibernation but before female bees do. Through evolution, these timings have synchronized, Whigham says. “But because of climate change, they’re getting out of synchrony.”
Many orchids use pollination strategies like the early spider orchid’s to lure specific insects or birds with the false promise of food or sex (see “The Science of Seduction,” above). When the deception results in an encounter, the unrewarded pollinator is loaded up with the orchid’s genetic material, poised to deposit it on the next orchid it visits. But not all pollinator-orchid relationships are known.
In 2018, conservation scientist Peter Houlihan and photographer Mac Stone set out to get proof of how the ghost orchid (Dendrophylax lindenii), one of the most well-known but inscrutable flowers on Earth, reproduces. It was long believed that the ghost orchid was pollinated by the giant sphinx moth because the insect’s proboscis, or tongue (which can unfurl to twice the length of its body), is designed to sip nectar from long-tubed flowers like the ghost orchid, but no one had ever photographed the moth in action.
That October, Stone found himself strapped to a cypress tree, 50 feet in the air, checking a remote camera trained on the largest known ghost orchid, the “super ghost.” It’s located in the National Audubon Society’s Corkscrew Swamp Sanctuary in the Florida Everglades. Houlihan, strapped nearby, motioned to Stone with his hands: Thumbs up? Thumbs down? Did Stone get the shot?
Stone used his phone to snap a photo of the camera’s screen and sent it to Houlihan, who gaped at what he saw. The photo showed a moth interacting with the ghost orchid. Other images showed additional species of moths. Houlihan finally had evidence that the long-held theory that only the giant sphinx pollinated the ghost orchid was wrong. The plant was not reliant on a single species of moth. Understanding the orchid’s reproductive biology may have been a difficult, years-long effort, but preserving the ghost might be a smidge easier than anyone had thought possible.
The two celebrated while strapped to the tree. An article followed in the journal Nature. One more orchid mystery put to rest—kind of. Because even as scientists delighted in the knowledge that the ghost orchid’s future was not tied to a single insect, a host of new questions—including whether the giant sphinx actually pollinates the flower or just drinks its nectar—unfurled in its wake.
Quote: Deborah Landau
Scientists like Houlihan have only begun to unravel the natural history of this vast plant family. In some cases, they’re discovering just how resilient orchids can be.
On the Eastern Shore of Maryland, McCormick is studying an orchid so rare it was thought to have vanished until it was spotted in 2009 on TNC’s Nassawango Creek Preserve. The plant (Platanthera x canbyi) is a hybrid of two orchids that are considered rare in the state: the white fringed and the crested yellow.
Deborah Landau, the TNC ecologist who helps manage the property, considers the reappearance of the orchid a sign of the plant’s vigor. The last recorded sighting of the lemon-colored orchid had been 18 years earlier—just after a wildfire burned through the landscape. There had been no sign of the plant since. Until suddenly—after controlled burns—the plant was spotted thriving on a former loblolly pine plantation that had been clear-cut and then restored to ecological health.
“It’s just crazy to think that these plants want exact factors,” says Landau. “But we do a fire and boom! When the right conditions are there, they come back. It just gives me a lot of hope.”
McCormick, along with a postdoctoral fellow in her lab, Ida Hartvig, is studying hybrid orchids from Nassawango Creek and other landscapes, including TNC’s Green Swamp Preserve in North Carolina. They are analyzing, among other things, how orchid hybrids form and how and what hybrids suggest about the development of new species.
“If, for example, the hybrid used some totally different fungi from what either of its parent species use, then it might grow in a very different place,” says McCormick. “It might develop into a new species because it then would not have the opportunity to back-cross with either of the parents.”
Looking at patterns in the genomes can help researchers determine how recently the plants have begun to distinguish themselves as new species. In other words, the scientists are studying real-time evolution to better understand the genetic diversity of the orchids and how to restore them.
Orchids are rarely incorporated into landscape-restoration plans because of the complexity of their needs, says David Remucal, curator of endangered plants at the University of Minnesota. Remucal is leading an effort at the University’s Minnesota Landscape Arboretum to sample every orchid native to the state—a collection effort that shares plant matter and collaborates with the North American Orchid Conservation Center.
But, Remucal argues, with more knowledge that could change. He’s also leading an effort to incorporate the white lady’s slipper into a prairie restoration project on TNC’s Regal Meadow Preserve in Minnesota. No one is certain it will work the first time. Remucal wonders whether such recently replanted ground will have the necessary fungi to support the orchids. But it’s a start, he says.
At the same time, the particularity of orchids that makes them hard to restore also makes them a sign for conservationists like Landau that other restoration efforts are working—in her case at both Nassawango Creek and the undisclosed preserve in western Maryland.
On that spring day, while the team observed and documented the condition of the white lady’s slipper, Landau considered what its presence means for the landscape itself, and the years of work her team has put into protecting it.
“There’s so much that we don’t know,” Landau says. “But we know that when [orchids] show up, we’re doing something right. It’s almost whatever the opposite of a canary in the coal mine is. It shows us that we’re on the right track in a really pretty way.”