Extreme Botany: The Precarious Science of Endangered Rare Plants


To save plants that can no longer survive on their own, Steve Perlman has bushwhacked through remote valleys, dangled from helicopters, and teetered on the edge of towering sea cliffs. Watching a video of the self-described “extreme botanist” in actio­­n is not for the faint-hearted. “Each time I make this journey I’m aware that nature can turn on me,” Perlman says in the video as he battles ocean swells in a kayak to reach the few remaining members of a critically endangered species on a rugged, isolated stretch of Hawaiian coastline. “The ocean could suddenly rise up and dash me against the rocks like a piece of driftwood.”

When he arrives at his destination, Perlman starts hauling himself up an impossibly steep, razor-sharp cliff 3,000 feet above the sea without a rope, his fingers sending chunks of rock tumbling down to the waters below. Finally, he reaches the plants and painstakingly transfers pollen from the flowers of one to those of another to ensure that the species can perpetuate itself. At the end of the season, he will return to collect any seeds they were able to produce.

Among the plants for which Perlman, a rock-star botanist with the University of Hawaii’s Plant Extinction Prevention Program, has repeatedly risked his life is Brighamia insignis, better known as cabbage-on-a-stick. One of the strangest-looking species in the Hawaiian flora, with a thick, swollen stem crowned by a rosette of fleshy leaves resembling a head of cabbage, it typically reaches 3 to 6 feet high but has been known to grow up to 16 feet tall. The plant once dotted seaside precipices on two Hawaiian islands, including the spectacular fluted cliffs of Kauai’s Nā Pali coast. But feral goats, rats, and invasive weeds brought to the islands by Polynesians and, later, Europeans decimated the species. What’s more, by the 1970s scientists had come to suspect that it had lost the large moth that they believe once fertilized its fragrant, creamy yellow, trumpet-shaped flowers. Without its pollinator, the plant was unable to produce seeds and its future in the wild was doomed. Had Perlman not come to the rescue, the plant would have faced almost certain extinction.

“When only a few members of a plant species remain, you need to make sure that every little bit of genetic diversity is preserved.”

The fate of cabbage-on-a-stick is now in the hands of another group of emergency botanists. Jeremie Fant, the head of Chicago Botanic Garden’s conservation genetics lab, and his colleagues are experimenting with procedures first developed at zoos to perform high-tech genetic rescue, including the development of a “studbook” that documents the pedigree of surviving individuals of the imperiled species in order to make last-ditch cross-breeding programs possible.

“When only a few members of a plant species remain,” says Fant, “you need to make sure that every little bit of genetic diversity is preserved.”

Scientists like Perlman and Fant work on the knife edge of last-ditch botany to save critically endangered plants like cabbage-on-a-stick because these species can’t produce enough seeds on their own. Plant conservation relies heavily on seed banking. Ideally, seeds are strategically collected from wild populations to ensure that as much of a species’ genetic diversity as possible has been captured. However, a considerable number of plants are so-called exceptional species that cannot be preserved in conventional seed banks. Some are so rare that they suffer from inbreeding and other genetic ailments that impede reproduction, and they don’t produce enough seeds to be banked. Some produce “recalcitrant” seeds that cannot be stored in seed banks because they can’t survive drying and freezing.

The plant known as cabbage-on-a-stick (Brighamia insignis) has been grown at Limahuli Garden & Preserve on Kauai, which is within the historic range of the species.

The plant known as cabbage-on-a-stick (Brighamia insignis) has been grown at Limahuli Garden & Preserve on Kauai, which is within the historic range of the species. Seana Walsh

According to Valerie Pence, director of plant research at the Cincinnati Zoo & Botanical Garden’s Center for Conservation & Research of Endangered Wildlife, a conservative estimate is that about 9 percent of threatened species fall into this category. If, as some scientists suspect, as many as one-third of the 500,000 plants believed to exist on earth are at risk, that means that 15,000 exceptional plants could require the kind of botanical intensive care that Perlman and Fant have provided for cabbage-on-a-stick.

Pence has pioneered still another field of emergency botany, developing protocols for in vitro propagation of many exceptional plants and for preserving them in a deep freeze in what she calls “frozen gardens.” But, she says, “the point is that there are a lot of species that will require methods other than traditional seed banking, and some of those methods require additional labor, facilities, and expertise, and are thus more expensive. The question is how are we going to meet this challenge?”

Among the planet’s exceptional plants are not just rare island endemics like cabbage-on-a-stick, but evolutionary relicts such as cycads, palm-like plants with stout trunks, arching crowns of stiff, evergreen leaves, and a 300-million-year lineage, older than any other surviving complex life form. They also include a variety of ecologically and economically important plants around the globe, from oaks and conifers to pawpaws and palms.

Today, only one lone cabbage-on-a-stick plant survives in the wild. It is on the Hawaiian island Kauai and is unable to reproduce.

To ensure the health of their animal populations, zoos and aquariums have for decades engaged in a kind of collaborative family planning. The first studbook created for conservation purposes was set up in 1932 for the European bison. Today, according to Kristine Schad, director of the Association of Zoos and Aquariums’ Population Management Center, studbooks are an integral part of the “Species Survival Plans” for more than 500 animals in the care of members of the organization, which represents over 230 institutions in the United States and abroad. The studbook for each species includes information on the individual animals at zoos and aquariums around the world, such as where they live, who their parents were, where their ancestors came from in the wild, whether they have been bred before, and if so, with whom.

Genetic and population analyses assist with the matchmaking, helping the institutions determine which animals should be bred with each other to ensure that populations are stable, inbreeding is avoided, and all the lineages present in the collective gene pool are preserved in living animals. The goal is to secure stable and genetically diverse populations for the future, and in many cases, to increase the number of animals to replenish depleted populations in their natural habitats.

Some 40 years ago, when Perlman set out to save cabbage-on-a-stick, a couple of hundred plants still grew on the Hawaiian island of Kauai. But two hurricanes destroyed most of them, and today, one lone individual is believed to survive in the wild, unable to reproduce.

A botanist collects pollen from the flower of Brighamia insignis.

A botanist collects pollen from the flower of Brighamia insignis. National Tropical Botanical Garden

Yet the species is more fortunate than many plants on the brink of extinction because, thanks to Perlman’s efforts, it has already been brought into cultivation. Perlman was able to reach and collect seeds from 15 different plants. These were propagated, and hundreds of specimens now grow at various locations operated by Hawaii’s National Tropical Botanical Garden, including Limahuli Garden, close by the species’ natural habitat along the Nā Pali coast. The progeny of these plants are also found in at least 57 botanic gardens around the globe. In addition, hundreds of thousands of specimens have been propagated and sold in recent years by commercial nurseries in the Netherlands. With so many plants safely in cultivation, cabbage-on-a-stick “will not go extinct in my lifetime,” Perlman says.

Recently, however, it became apparent that the National Tropical Botanical Garden’s cabbage-on-a-stick plants were not producing seeds as readily as they once did. Fant and his colleagues decided to help figure out why. Using a database managed by Botanic Gardens Conservation International (BGCI) that includes plant records from about 1,500 of the more than 3,000 botanic gardens worldwide, they tracked where else cabbage-on-a-stick is growing in cultivation. They obtained plants from a number of botanic gardens in North America and Europe, did genetic testing, and discovered that some of the lineages once present in the Hawaiian garden’s plants had been lost. Apparently, the plants were beginning to suffer the effects of inbreeding.

The good news, according to Fant, is that the genetic sampling also found that much of the missing genetic diversity was present in plants at botanic gardens in Berkeley, Chicago, San Diego, and Switzerland, all of which trace their origins to the seeds Perlman collected. “There were six or seven individuals that could be bred back into the National Tropical Botanical Garden plants” to restore genetic diversity, increase seed production, and improve the species’ prospect for long-term survival, he says.

A scientist with the Plant Extinction Prevention Program climbs through remote Hawaiian ecosystems to study endangered plant species.

A scientist with the Plant Extinction Prevention Program climbs through remote Hawaiian ecosystems to study endangered plant species. PEPP

Over the past few decades, botanic gardens have taken the lead in efforts to save imperiled plants by creating a backup system in cultivation as a hedge against extinction in the wild. They not only have collected seeds and pollen for safeguarding in seed banks, but also have spearheaded efforts to propagate the species and reintroduce them to their natural habitats. Specialized botanic gardens such as Pence’s in Cincinnati are developing species-specific protocols for preserving a growing number of exceptional plants, including cryopreservation of embryos and other vegetative tissues in a state of suspended animation in liquid nitrogen at -321 degrees Fahrenheit.

One thing botanic gardens haven’t done, says Fant, is see plants as distinct individuals. “Zoos manage their animals as individuals,” he says, “but plants are usually maintained as a collection and rarely is any one individual perceived as a unique member of that species.” This has hindered efforts to save them. Without a studbook tracking the complete pedigree of each genetically unique cabbage-on-a-stick plant in cultivation, for example, it was impossible to ensure that no lineages were being lost. This, Fant and his colleagues wrote in a 2016 paper in the American Journal of Botany, “is clearly not a sustainable solution to managing the thousands of threatened exceptional plant species” held at botanic gardens around the globe.

“We need an eharmony for plants,” says Abby Meyer, executive director of BGCI in the U.S., referring to the popular online dating site. Meyer has proposed such a botanical matchmaking system, which she calls “integrated collections management.” Like the collaborative system employed at zoos, it would enable gardens to take into account the plants they grow as well as those at other institutions when making decisions about new plants to acquire, crossbreeding, and other measures to preserve the health and diversity of the plants in their care.

Given the grim state of plants around the globe, there’s no time to lose. Currently, says Craig Hilton-Taylor, head of the International Union for Conservation of Nature’s Red List of imperiled species program, 2,787 plants are considered “critically endangered,” defined as suffering “an extremely high risk of extinction.” In many cases, fewer than 50 individuals remain in the wild, putting these plants in a category known in bureaucratic parlance as “CR-D” species. Meyer points out that among these rarest-of-the-rare plants are 43 U.S. native trees, giving the country the dubious distinction of being tied for second place with Madagascar, behind China, as the country with the most CR-D trees.

Plant conservation has not generated nearly the same sense of urgency, nor the funding, that animal conservation has.

According to Hilton-Taylor, in addition to the critically endangered species, 4,269 plants on the Red List are deemed endangered, with “a very high risk of extinction,” and another 5,725 are considered vulnerable, facing “a high risk of extinction” in the wild. Because to date only 8 percent of known plant species have been assessed for inclusion on the Red List, these numbers are certain to rise.

To make matters still more precarious, only 41 percent of the known globally threatened species are protected in cultivation at botanic gardens, and according to Meyer, many are held at just a single institution. She notes that one-third of North American native threatened species are found at only one garden, leaving them at risk from pests, diseases, storms, and other disasters.

Yet plant conservation has not generated nearly the same sense of urgency — nor the funding — that animal conservation has. In the U.S., for example, plants receive just 5 percent of federal dollars spent on species conservation.

A male Wood’s cycad, Encephalartos woodii, of South Africa. The species survives today only in cultivation.

A male Wood’s cycad, Encephalartos woodii, of South Africa. The species survives today only in cultivation. Kew Royal Botanic Gardens

In 1999, American biologists James Wandersee and Elisabeth Schussler coined the term “plant blindness” to describe humanity’s inability to appreciate the ecological and economic importance of plants, or even to notice the plants all around them. Botanists also blame our lack of empathy for plants for our failure to grapple with the growing threats they face. Consider that cycads, which are coveted by plant collectors because of their beauty and ancient pedigree, have suffered a worldwide poaching crisis worse than that of rhinos, elephants, and other so-called charismatic megafauna. As a result, 75 percent of cycad species are at risk of extinction, yet their plight is not even a blip on the public’s radar screen.

That is certainly not true for beloved animals. For example, when the mate of Tashi, a female rhino at the Buffalo Zoo, passed away, the zoo teamed up with Cincinnati’s Center for Conservation & Research of Endangered Wildlife, which for 10 years had been storing the sperm of Jimmy, a male Indian rhinoceros who had never sired a calf during his lifetime. Jimmy’s sperm was rushed to Buffalo to inseminate Tashi. Sixteen months later, in 2014, the birth of the baby rhino named Monica, conceived through artificial insemination to perpetuate the DNA of a bull that had been dead for a decade, was big news.

While beleaguered rhinos like Jimmy regularly make headlines, there are few heart-wrenching stories about plants like the male Wood’s cycad, Encephalartos woodii, of South Africa, the only member of his species, male or female, ever to be found alive. Today, he survives only in cultivation. Unlike Jimmy the rhino, the handsome cycad, with orange cones and a crown of bright green, 6- to 10-foot-long leaves, has no pet name. And unlike Jimmy, his species will never again reproduce and evolve freely in the wild.