Rare Tree Reveals First Flower

One of the world’s rarest trees is flowering in the greenhouses of the Missouri Botanical Garden for the first time. This latest development in the fight to save Karomia gigas from extinction is significant—it is the first time the flower of this plant has ever been observed by plant scientists or horticulturists, and possibly by anyone at all.

On the Edge of Extinction 

There are fewer than two dozen Karomia gigas trees known to exist in the wild, at two sites in Eastern Tanzania. The International Union for the Conservation of Nature (IUCN) Red List has assessed this species as Critically Endangered. While efforts are underway to conserve these trees in place (in situ), the Garden is also working with several Tanzanian partners to secure the future of this species outside of its natural habitat (ex situ).

We first introduced readers of this blog to Karomia gigas in 2018, after Garden horticulturists were able to successfully germinate seeds of the tree acquired from those partners in Tanzania.

Fandey Mashimba, Manager of Seed Biology for the Tanzania Forest Service Agency’s Directorate of Tree Seed Production, supervised the collection and shipment of these seeds. Mashimba also worked with Roy Gereau, Tanzania Program Director in the Garden’s Africa and Madagascar Department, to secure the necessary agreements for this international rescue effort. The Botany Department of the University of Dar es Salaam in Tanzania conducted the botanical survey and collecting that provided the basis for the seed collection. Dried specimens of the tree’s foliage and fruit are preserved in its herbarium.

Until this point, the tree had only been described by features like its foliage, bark, and its unique papery-rimmed fruits. Conservation efforts focused on those fruits, and the seeds inside, as the key to growing the next generation of Karomia gigas and saving it from extinction. 

Of the thousands of seeds sent to the Missouri Botanical Garden in 2018, only a handful turned out to be viable. Still, the work produced 29 seedlings representing the genetics of seven wild trees, about one third of the known population.

Karomia gigas trees under a shade cloth at the Missouri Botanical Garden. Photo by Cassidy Moody.

The First Flower 

Three years later, we have reached this milestone—the first of these seedlings to successfully reach maturity and produce a flower. The celebration was short-lived, as the flower faded within 24 hours. But it provided an important data point in the growing set of information we’re learning about this critically endangered species. 

“Knowing the characteristic of the flower gives us a wealth of scientific information that will allow the Garden and our Tanzanian partners to publish a complete description of the species for the first time, and will help to establish the species’ relationships with other species,” says Gereau. “The shape of the corolla (petals) already demonstrates that the species is correctly placed in the genus Karomia rather than in the closely related genus Holmskioldia (Chinese hat tree), an issue that was not completely resolved until now.”

We now know this species can reach maturity in three to four years. Some trees, like oaks, can take decades to produce their first acorns. This quick turnaround for Karomia gigas is important for the conservation of this species. The sooner it flowers, the faster it can produce seeds and the next generation of Karomia gigas

As each of the young trees reach maturity in our greenhouses, we will learn a little bit more about them, and the conditions that help keep them growing and thriving. We may be able to glean clues about environmental factors that induce flowering, such as emerging from a period of dormancy. And Justin Lee, the Senior Horticulturist taking care of these trees, attempted to self-pollinate the flower to gain insight into how best to produce fruits, and therefore, more seeds.

Photo by Cassidy Moody.

Aside from the flower itself, three years of observation have given us a great deal of information about the trees themselves, and how to hopefully keep them happy and healthy. They appear to be very particular when it comes to fertilizing and watering—and they’re not exactly fans of the St. Louis weather. 

“I’d say the most challenging thing about growing these plants has been trying to simulate their growing conditions in Tanzania. They grow in a very unique soil and climate that is nearly impossible to duplicate here in St. Louis,” says Lee. “This has certainly been a plant I’ve had to be extra careful with to observe and learn its requirements.  I’ve definitely felt a strong responsibility to care for these. They’re all we’ve got.”

Fighting for the Future 

The efforts to protect the future of Karomia gigas extend beyond this single flower, or even the 29 young trees in the Garden’s greenhouse.  

As confidence grows about the health and stability of the greenhouse population, Garden horticulturists can begin to test other methods of propagation without seed—such as tissue culture, cuttings, and air layering. Micropropagation Coordinator Caleb Dvorak has already seen some level of success using tissue culture. Healthy, mature trees will provide more living material to scale up that work, unlocking another avenue to keep this species safe. 

Understanding the success of these methods not only benefits our efforts ex situ, but also allows for better care and protection of this species in-country. 

Micropropagation of Karomia gigas. Photo by Cassidy Moody.

Another goal is to protect the future of Karomia gigas through seed banking, if possible. Orthodox seeds can be dried, frozen at sub-zero temperatures, and later brought out of deep-freeze and germinated. With enough seed secured, the Garden can test to see if the seed of this species is orthodox, and therefore a good candidate for seed banking. Seed banking is a valuable back-up in case of the loss of the living trees. 

The Garden is also now working with our Tanzanian partners to secure genetic material from all known individuals in the wild. The goal is to save the species by retaining as much of its genetic diversity as possible in the wild, in ex situ living collections, and seed banks. Genetic analysis will allow us to target specific individuals, and conduct controlled crossing of mature trees to best capture that important genetic diversity. 

As this critical conservation work continues in our greenhouses, plans are also developing to eventually include a Karomia gigas on display in the Climatron for Garden visitors to see. And more importantly, this work will help ensure the future of these trees in their native habitat.

Cassidy Moody
Senior Digital Media Specialist

Leave a Reply