- Working with South African daisies, Colombian magnolias and Philippine coffee trees, botanists the world over are discovering the secrets to bringing extremely rare and threatened plants back from the brink of extinction. Reintroductions are often the only way to build back thriving populations, but scientists face numerous hurdles.
- A major barrier is lack of botanical knowledge about rare species, making it hard to produce sufficient viable seeds, determine triggers for germination, and identify suitable seedling habitat. If seeds aren’t available from rare plants, botanists must use cuttings to propagate plants.
- Newly established plant populations often need help in the face of numerous threats. Climate change, for example, can not only create harsh new growing conditions but also fuels the spread of plant pests. Young plants frequently need to be protected from human activities like poaching, intentional burning or land-use change.
- While it can take decades for reintroduced plants to grow into sustainable, self-replenishing populations, project funding is often limited to three years or less, especially in the Global South. Experts say they hope funding will increase as recognition grows that ecosystem restoration requires plant diversity, including rare species.
It was 2006 and Ismail Ebrahim, a botanist with the South African National Biodiversity Institute (SANBI), was worried. While surveying one of the last remaining patches of renosterveld shrubland in South Africa’s Paarl region, near Cape Town, he and his team of citizen scientists found a small, yellow-flowered daisy species: Marasmodes undulata.
It had long been thought extinct, with the last 200-strong population observed at the same location near the town of Paarl in the 1980s. Now, Ebrahim’s team had discovered an even smaller population, numbering just 27 individuals.
The citizen scientists had to act quickly to stave off species oblivion. Competing vegetation was choking out the small daisies, so Ebrahim’s team took the calculated risk of setting fire to the site to level the playing field and stimulate seedling growth for the fire-adapted daisy.
But no M. undulata reappeared at first, and those popping up in subsequent years disappeared. “Every time we went back to the site, we found less plants,” Ebrahim recalls.
Why put so much focus on conserving a diminutive shrubland flower? Among the diverse inhabitants of the renosterveld, few species are more easily overlooked than M. undulata, which botanist Donovan Kirkwood of Stellenbosch University Botanical Garden affectionately called the “ugly duckling daisy” before his untimely in August. But just like other renosterveld plants, M. undulata belongs there, forming part of an ecosystem that becomes more sensitive to collapse with every species that is lost. Like a Jenga tower block, the little daisy helps keep the broader whole intact.
Starting in 2019, Ebrahim and his team took further action to prevent extinction. Using a batch of seeds botanists had collected decades earlier, they tried to raise and propagate the daisy. If the reintroduction was successful, they hoped M. undulata could be brought back from the brink. But only time would tell.
Saving the world’s rare plants
Rescue missions like this one are more urgently needed than ever. Today, some estimate that around 45% of the world’s flowering plants are threatened with extinction, and reintroductions to the wild are the only way to save many. But, as Ebrahim and colleagues learned, relying on scant individuals to restore a flourishing, self-sustaining population requires a long, difficult journey.
Unlike the world’s charismatic animal species, rare plants get far less conservation attention, and baseline botanical knowledge is often lacking. Researchers trying to save them must start from scratch, discerning the biology of each species as they go.
For some plants, seeds aren’t even available. If they are, researchers must learn what triggers germination. Then there’s the problem of ensuring young plants survive in the wild, protecting them from ongoing natural and human threats. All this usually must be done on a shoestring budget, with challenges especially acute in the Global South, where long-term conservation funding is a perennial problem.
In spite of these challenges, innovative plant reintroduction projects are underway the world over today as botanists work to secure a permanent place on Earth for threatened species like the M. undulata daisy in South Africa, rare magnolias in Colombia’s cloud forests, and threatened wild coffee plants in the Philippine rainforest.
“There is no technological reason why any plant species should become extinct,” said Paul Smith, secretary-general of Botanic Gardens Conservation International (BCGI), an NGO that supports hundreds of global plant recovery projects. “There are some that are more difficult than others, but really, it’s a question of just applying ourselves.”
Deciphering the secrets of rare plant propagation
Germinating rare plants is a tricky business. Botanists often start with miniscule numbers of seeds for plants with naturally low germination rates. At the start, germinating conditions are often a mystery, with each species having specific light, water, temperature and soil nutrient requirements. Germination triggers can be wildly strange, with species like Vanilla planifolia germinating better when exposed to acids akin to the bile in an animal’s digestive system, while others like Foetidia rodriguesiana thrive on tortoise dung.
Botanists often look to germination protocols of related, more abundant species for clues. But that wasn’t possible for M. undulata, because most of the 14 species in the Marasmodes genus are also threatened, said SANBI’s seed conservation program manager Victoria Wilman. It would take trial and error to crack the daisy’s germination code.
None of the seeds from a batch collected in the 1980s sprouted, probably because they were too old or poorly stored, Ebrahim said. But the team held out hope for several hundred seeds stored at Kew Gardens’ Millennium Seed Bank in the U.K., which has partnered with SANBI to collect and store seeds from 6,500 South African species.
Two teams of botanists — SANBI’s group at Kirstenbosch National Botanical Garden and Kirkwood’s team at Stellenbosch — searched for the ideal germination conditions. They carefully tested different treatments: with or without smoke, a known germination trigger in fire-prone ecosystems like the renosterveld shrubland.
“It’s really nerve-wracking to actually work with these species because it’s … the last few [existing] individuals,” Ebrahim said. Six seeds sprouted, most of which had been smoke-treated.
From those few seeds, the team raised young plants, hand-pollinating them to stimulate more seed production. Some of those seeds were used to replenish the Kew seed bank. The rest sprouted into more plants. Cuttings were also used for propagation.
“Every year we have anywhere from between 100 and 200 new little plants,” ready to be reintroduced to native South African soil, said Annerie Senekal, an acting curator of Stellenbosch University Botanical Garden.
Back from the brink in the Philippines
But what about endangered plants for which no seed bank stock exists? This includes Psychotria ilocana, a member of the coffee family native to the rainforests of Ilocos province in the Philippines.
Michael Calaramo, director of the Philippines’ Northwestern University Ecological Park and Botanic Gardens, and his colleagues spent two decades trying in vain to find the tree where it had been described by European and U.S. explorers more than a century ago. But much of its rainforest habitat has been cleared for pasture or renewable energy projects.
Then, in 2023, Calaramo chanced upon one individual at a site destined to become a wind farm. “The botanic garden was able to rescue the lone surviving tree, salvaged as a small, balled specimen from construction debris … destined for landfill,” Calaramo said.
But how to reproduce a tree from a single individual? The team tried brushing pollen from one flower to another, but no fruit formed. Calaramo suspected that, like other Psychotria species, P. ilocana requires specific pollinators capable of transferring pollen to the female reproductive parts of the flower. So he hired an entomologist to study the pollination of other Psychotria species to determine how best to replicate this process for P. ilocana.
As the team experiments with planting P. ilocana cuttings, their hope is still to obtain seeds that have more genetic diversity and may offer a better chance of producing plants able to survive in the wild.
“Otherwise [what we’re producing] will just be a clone of a single specimen,” Calaramo explained.
Rare plants at the brink require desperate means
Scientists in Mauritius, an island nation in the Indian Ocean, have encountered an especially devilish germination challenge with Zanthoxylum paniculatum, a critically endangered forest species endemic to Rodrigues Island.
Cuttings from two of the last three remaining wild Z. paniculatum trees didn’t grow, and none of the plants’ seeds germinated. However, grafting Z. paniculatum cuttings onto a Zanthoxylum heterophyllum, a related, more abundant species from the main island of Mauritius, did work. “As of now, we have nine grafts which are surviving,” said Sweety Edouard, scientific officer at the Rodrigues-based nonprofit Mauritian Wildlife Foundation.
But these grafted plants aren’t yet allowed to be reintroduced to Rodrigues Island. So the research team is employing a technique called air layering to obtain more Z. paniculatum plants.
This involves cutting into the Z. paniculatum branches, adding rooting hormones and other substances to the injured stem, and covering it with plastic to retain humidity. When a root begins to grow, “you can chop down this part, and [eventually] you have a tree,” said Bunty Seeruttun, the flora manager at the Mauritian Wildlife Foundation.
While having just a few remaining individuals of a plant species can make it less resilient to threats, limited genetic diversity should never be a reason not to attempt reintroduction, said Carlos Magdalena, a scientific and botanical research horticulturalist at Kew Gardens.
“I believe you can restore any plant species with very few specimens,” he said. A few decades ago, Magdalena succeeded in propagating seedlings from a single café marron plant from Rodrigues Island, which has since been reintroduced there. “By not listening to negative thinking, I managed to demonstrate [this] is possible,” he said.
Back to the wild
Getting seedlings started is sometimes the easy part. A case in point: Botanical gardens have long grown the toromiro tree, Sophora toromiro, from seeds collected decades ago before the tree went extinct on Rapa Nui, or Easter Island.
But in a historic attempt to reintroduce the tree to its home in the 1980s, “all the material failed,” said forestry engineer Jaime Espejo of Chile’s Viña del Mar Botanical Garden and the University of Concepción. The reason, researchers speculated, was the lack of rhizobia — root nodule bacteria that legume species like the toromiro tree require to obtain nitrogen from the soil, explained Macarena Gerding of the University of Concepción.
While the toromiro tree thrives in the well-fertilized, microbe-rich soils of botanical gardens, it couldn’t grow on Rapa Nui without its rhizobia — which was no longer present there, something Espejo and Gerding determined during island soil tests.
So the scientists isolated rhizobia from other Sophora species in Chile and New Zealand and used them to inoculate young toromiro seedlings.
This was a winning solution: Of the toromiro trees planted at a Rapa Nui nursery in 2018, specimens inoculated with the Chilean and New Zealand root nodule bacteria mostly survived, whereas uninoculated trees didn’t.
Soon, Espejo plans to reintroduce young toromiro trees at the site of the last known wild individual toromiro, inside the Rano Kao volcano. It’s hoped that when reintroduced trees eventually become more numerous, they will one day provide wood used for traditional carvings and other cultural artifacts as in the past.
Location, location, location
Seedling survival rates can still be poor even when plants seemingly have all the basic ingredients to thrive. Sometimes it’s a matter of site selection: Species are often reintroduced to the last location known to support wild individuals. But that doesn’t guarantee optimal conditions, Magdalena explained.
Once a rare plant is reintroduced, it still requires good growing conditions, which means more trial and error, said Sebastián Vieira, the cofounder of Corporación SalvaMontes Colombia. Since 2016, the organization has been working to conserve Magnolia polyhypsophylla, a tree endemic to the cloud forests of Colombia’s Alto de Ventanas region, and one of the most threatened of the country’s 42 magnolia species (41 of which are endangered due to deforestation and overuse for timber).
Vieira and colleagues have succeeded in growing 178 young M. polyhypsophylla trees using several thousand seeds obtained from roughly 70 known adults.
They’ve been planting them at various sites to identify ideal habitat. The best, they found, lie on the edges of well-preserved forests and pastures, where new forest is regrowing, guaranteeing the trees adequate sunlight but protecting them with smaller trees or tall grasses. About 90% of saplings have survived in edge areas, compared to 70% in open pasture, Vieira said.
“They grow quicker and healthier,” he noted. “We have been able to substantially increase the amount of trees in their habitat.”
For Marasmodes undulata, the South African daisy, there may be better-suited growing sites than the tiny 6-hectare (15-acre) conservation area near the town of Paarl where it’s being reintroduced. But the species has only ever been recorded there, and other options are limited; 95% of original renosterveld habitat has been lost to agriculture and urban development.
In 2023, a team from Stellenbosch, SANBI and the citizen scientist group planted M. undulata seedlings at the Paarl site, always during rainy winter months to give the plants a chance to establish before summer. But survival was poor. For the first two years, “basically none of the planted-out plants … survived,” Senekal said.
This may be because plants coddled under nursery conditions can’t adjust to harsher wild environments — even when botanists subject them to a period of stress before planting.
Ebrahim, Senekal and colleagues are trying various strategies to improve survival — watering the plants during the first summer after restoration, planting them out earlier in the year to give them more time to establish, and planting 2-year old seedlings instead of 1-year-olds. But evaluating success takes time.
In a good sign, the population of daisies is very slowly expanding, Ebrahim said. “If we didn’t start this project in 2019, the species most certainly would have been extinct by now,” he added.
Reintroduction in a rapidly changing world
As scientists seek out the perfect historical habitats, they’re also forced to account for how natural landscapes have been transformed by land use and climate change. Many endangered plants are now being reintroduced to ecosystems very different from the ones they evolved in.
Pollinators or seed-dispersing animals may be scarce or absent. Mauritius, for example, has become drier, while in Colombia, climate change has aided the spread of beetle larvae that feed on the branches of Magnolia polyhypsophylla, gobbling away up to 75% of the trees’ crowns, Vieira said. His team is cutting off affected branches while enlisting local academics to find ways to control beetle populations.
Elsewhere, newly established plants need to be protected from seed-eating rats, seedling-smothering invasive plants, and human activities like poaching and fires. It’s a widespread misconception “that we can just spread some seed in already human-transformed landscapes and hope for the best,” said Smith from Botanic Gardens Conservation International. The “chances of success are even lower [there] than they would be in nature.”
Funding, collaborations and community involvement
It can take decades for reintroduced plants to grow into self-replenishing populations; Ebrahim reckons it will take at least another five years for Marasmodes undulata, while Vieira’s magnolias will only begin to mature and produce fruit when they’re 12 years old.
Giving plants the continuous attention they need over time is especially challenging in the Global South, where restoration projects often rely on funding from Global North governments and NGOs, which typically fund projects on short cycles of three years or less, said Alex Hudson, who manages BCGI’s Africa-based projects.
He said he hopes rare plant reintroduction funding opportunities will increase as institutions recognize that fully successful ecosystem restorations should seek to build back the native diversity of plants, something that isn’t achieved when planting fast-growing, nonnative species (a strategy that is attracting private funding as a source of carbon credits).
Some botanists are searching out novel funding sources; Calaramo’s team is exploring practical uses for Psychotria ilocana — as a source of pharmaceutical compounds, for example — to attract conservation interest from government or private investors.
Building lasting relationships with local policymakers and communities is also key to sustaining reintroduction efforts. Hiring locals for reintroductions not only helps support livelihoods but also gives people a sense of ownership and interest in protecting ecosystems, Hudson said.
SalvaMontes is training farmers to grow magnolia trees on their properties, while also doing magnolia educational workshops with adults and schoolchildren. Rather than being only a source of timber, “magnolias are now [seen as] something special for people in the region,” Vieira said.
Botanists, like most conservation scientists, are learning how to creatively meet the challenges of reintroduction. Year by year, even as human threats mount, they see their efforts bloom. And they know that learning the secrets of reintroduction for one species, like Marasmodes undulata, may help spur new knowledge to bring back another.
“It is very encouraging to go back every year with a group of people who are dedicated and motivated to find solutions to this problem,” Senekal said. Hopefully, “we’ll get to a point where we can do this for quite a lot of other [plants] that need the same attention.”
Banner image: Fruit from one of the 70 last known adults of the endangered tree Magnolia polyhypsophylla. Image courtesy of Sebastian Vieira.
Citations:
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Šoch, J., Šonka, J., & Ponert, J. (2023). Acid scarification as a potent treatment for an in vitro germination of mature endozoochorous Vanilla planifolia seeds. Botanical Studies, 64(1). doi:10.1186/s40529-023-00374-z
Magee, A.R., Ebrahim, I., Koopman, R., von Staden, L (2017). Marasmodes (Asteraceae, Anthemideae), the most threatened plant genus of the Cape Floristic Region, South Africa: Conservation and taxonomy. South African Journal of Botany, 111, 371-386. doi:10.1016/j.sajb.2017.04.006
Espejo, J.E. (2022). Early results in reintroduction of Sophora toromiro (Phil.) Skottsb. in Rapa Nui: Species Extinct in the Wild (EW). Conference: Early results in reintroduction of Sophora toromiro (Phil.) Skottsb. in Rapa Nui: Species Extinct in the Wild (EW)
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