On a bench in the Missouri Botanical Garden greenhouse, there sits a handful of seemingly unassuming seedlings. They are only a few inches tall and just beginning to show their true leaves. Their small stature belies the enormity of the efforts to save this plant from extinction.
Karomia gigas is, after all, one of the rarest trees on the planet. The dozen or so sprouted seedlings in the Garden greenhouse represent nearly half of this species’ entire known population.
Getting to this point has been a collaborative effort between the Garden’s research and horticulture divisions. Together with Tanzanian government agencies and conservation groups, the hope is to bring this species back from the brink.
What is it?
Karomia gigas is a member of the mint family (Lamiaceae). Your home herb garden is probably filled with some of its botanical relatives—oregano, rosemary, thyme. But this plant is much bigger than those culinary herbs. One tree was documented at more than 80 feet tall. It has large, ovate leaves and a mottled orange trunk. But this species truly stands out because of the unique structure of the tree’s fruit. The small, dry fruiting body is surrounded by an expanded and strongly veined calyx.
The species was first discovered in 1977 from a single tree and sapling found in Kenya. By 1985, both of those individuals had been cut down. Herbarium specimens made from this site in 1977 and again in 1980 play a key role in identifying new specimens despite the trees themselves being lost.
Karomia gigas was feared extinct for nearly a decade until a single tree was found in southeastern Tanzania in 1993, some 380 miles away from the original discovery site in Kenya. In 2011, Tanzanian botanists discovered a second population several miles away. Roy Gereau, Tanzania Program Director in the Garden’s Africa and Madagascar Department, participated in the publication of the rediscovery of this species.
Saving the Species
Today, there are only 19 trees known to exist in the wild. Its natural habitat, in the coastal forests of Eastern Africa (Somalia, Kenya,Tanzania, and Mozambique), is one of 35 ‘biodiversity hotspots’ around the world.
Term to Know – Biodiversity hotspot. A biodiversity hotspot is a threatened area with a high percentage of plant life found nowhere else on earth. Although they only comprise 2.3% of the earth’s surface, these hotspots are home to more than 50% of the world’s plant life.
The remaining Karomia gigas are located in forest reserves, but surrounded by logging and charcoal operations, exerting extreme pressure on their environment and leading to the designation of Critically Endangered on the IUCN Red List.
The Missouri Botanical Garden took part in a field survey of six trees in 2016, along with others from the Tanzania Tree Seed Agency (TTSA), the Tanzania Forest Service (TFS), and Botanic Gardens Conservation International (BGCI). In addition to visiting the trees and mapping their exact location, Garden staff also provided training for critical skills such as GPS mapping, collecting seed, taking data, and making herbarium vouchers.
There was no viable seed to collect during the 2016 field survey, but expeditions in 2017 and 2018 yielded mature fruit from several of the trees. The first attempts to study and germinate the seeds were carried out in Tanzania by the TTSA. The agency was able to germinate some seed, but the sprouts quickly rotted away. The study did, however, reveal valuable information such as environmental factors, seed maturity, and viability.
The Garden signed an agreement for seed export with the Tanzanian government in late 2017, and finally received a large shipment of fruits in September of 2018.
Getting it to Grow
One of the biggest challenges for propagating the species is its extremely low seed viability. In its native environment, the seed is susceptible to a fungus that can cause it to rot before it develops. Of the nearly 6,500 fruits shipped to St. Louis, only 111 contained potentially viable seed. Horticulture staff extracted and cleaned each seed by hand, a process that took more than 18 hours.
Because it has never been successfully grown in cultivation before, Garden horticulturists are essentially starting from scratch when it comes to caring for this plant. They’re using clues from its natural habitat, such as temperature range, rainfall, seasons, and soil type to determine the best growing conditions.
The propagation team monitors the seedlings for small changes that could indicate a problem, such as browning leaf tips caused by over-watering, and adjusts cultivation techniques accordingly.
The magnitude of this work isn’t lost on those tasked with trying to pull it off.
“On one side of the coin it’s a little scary because very rare species like this are depending upon us and we can’t get it wrong,” says Andrew Wyatt, Senior Vice President of Horticulture and Living Collections. “Personally, and I know others on my staff feel this way too, it is actually amazing and exhilarating. It is such an honor to use one’s skill to save a species from extinction.”
What Happens Next?
The young trees will be kept in Garden greenhouses until they are large enough to test other propagation methods such as cuttings and grafting. If the trees begin flowering, staff will hand-pollinate them to maximize the genetic pairings between individuals. Increasing the genetic diversity of the remaining trees is key to preserving the species in the long run.
Being grown in a more controlled environment could also help increase the viability of seed. At that point, some seed would be stored in the Garden’s seed bank. Seed could also be sent back to Tanzania, along with all the propagation and cultivation data collected here, to attempt returning this species to its native habitat.
Eventually, at least one tree will be planted in the Temperate House so visitors can see this rare species up close. Maintaining Karomia gigas as part of the Garden’s living collection is just one more way of safeguarding it against extinction.
The story of Karomia gigas is far from an isolated case. Gereau has assembled a list of nearly 500 tree species in Tanzania that could be targeted for similar seed collection, propagation, and conservation. Thanks to its 35-year history of plant science and study in the region, the Garden is uniquely positioned to help make a difference. “Building on our past experiences and established relationships, we can do a great deal to help build Tanzania’s capacity to conserve its biodiversity and the habitats on which it depends into the future,” says Gereau.
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Cassidy Moody – Digital Media Specialist
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