The Karomia gigas trees growing at the Missouri Botanical Garden are three years old and already about six feet tall.
Only about two dozen are known to grow in the wilds of Tanzania. Roy Gereau, the Tanzania program director at the Missouri Botanical Garden, wasn’t too surprised the flower hasn’t yet been spotted. Karomia gigas is a tall, straight tree that can reach 80 feet whose branches don’t appear until about 35 to 40 feet off the ground, making the flowers hard to spot.
The tree is so rare, it doesn’t have a known nickname in English, Swahili, or the local languages around the forest reserves it's found in. Of the more than 60,000 tree species known to exist, the Karomia gigas is among the closest to extinction and one of the most endangered in Africa.
“To the best of our knowledge, there certainly is no record of the flowers in the scientific literature,'' says Gereau.
And now that the tree has produced a flower, its conservators are confident they can keep it from disappearing.
“From a standpoint of actual extinction, it’s looking really good,” says Andrew Wyatt, the vice president of horticulture at the Missouri Botanical Garden. “We can make sure the species doesn’t go extinct.”
Growing the trees abroad
Growing the plant has been a challenge. In the wild, it’s highly susceptible to a fungus that may be spread by insects.
In September 2018, thousands of seeds were collected from field expeditions in Tanzania and shipped to St. Louis, but only about 100 seemed viable. To complicate matters, Karomia gigas' growing conditions in its Missouri greenhouse had to replicate the soil, water intake, and sunlight of the East African climate it evolved in.
The horticulturalists were eventually able to grow saplings by first germinating the seeds on wet paper towels to reduce the likelihood of an infection, and then planting them in peat. There are now 30 young trees grown from seeds and one propagated from a cutting.
“We were debating whether it would flower in our careers,” Wyatt says.
With so few trees from this species left in the world, trying to save them and seeing them grow successfully is emotional.
“You celebrate every stage. They become like your children. You’re a steward to these species,” Wyatt says. “You have a scientific connection, and you also have an emotional connection to the species.”
Lee agrees: “They’re kinda my babies.”
The flower helps scientists better understand the tree, confirming it’s in the right genus and, based on the shape of its petals and stamen, likely pollinated by insects. It’s unclear if flowers on adult trees will grow singularly or in clusters.
“The single flower ... may not be the normal arrangement,” says Gereau. “It’s a juvenile putting out a flower for the first time.”
Importantly, it also helps secure the tree’s survival. Horticulturalists can propagate the plant with cuttings, but those trees are clones with the same DNA. Having genetic diversity in a species helps ensure it can resist deadly conditions like pests.
“Without flowering in our collections, we have to rely on the wild plants to produce seeds and the viability is very low,” says Wyatt. While some species can pollinate themselves, it’s unclear if Karomia gigas can. Lee hand pollinated the species before the flower wilted but says having more flowers from more trees will help produce more genetically resilient plants.
“Towards the end of the day I spread some pollen around. It's kind of a question mark how readily some plants self-pollinate. Sometimes it’s like a sliding scale. This one was not successful,” says Lee. “Ideally since we have so many [saplings], we will be able to get that flowering consecutively and cross pollinate, and that's better for genetic diversity.”
“Having flowering plants is a great start in efforts to recover the species,” says Emily Beech, an expert on endangered trees at Botanic Gardens Conservation International. Though not involved with propagating the St. Louis trees, in 2016 Beech joined Gereau and others from the Tanzanian Forest Service on an expedition to document the conservation status of known trees.
“There were no visible seedlings in the forest when we visited but the fact that there are now flowering plants provides a real hope for the species in the future,” she says.
A step toward regrowth
The tree was first discovered in 1977 in Kenya, but when only two known Kenyan trees were cut down, it was thought extinct. It was rediscovered in Tanzania in 1993, and Gereau and Tanzanian botanists have been slowly finding more in the wild since 2011.
A close-up of the Karomia gigas leaf. In the wild, the trees have been observed dropping all their leaves during the dry season, PHOTOGRAPH BY CASSIDY MOODY, MISSOURI BOTANICAL GARDEN
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