1 August 2018

Rescued from danger and flown to safety

Kew scientists discover a critically endangered new plant species and secure its survival by conserving seeds at Kew’s Millennium Seed Bank.

Brown plant with moss-like appearance in running water.

New plant species

During a botanical survey along the banks of the Seli River, Sierra Leone, in April 2016, Kew scientist Xander van der Burgt, accompanied by Joseph Momoh from the National Herbarium of Sierra Leone, encountered a secluded population of an aquatic herbaceous plant growing in dense patches on the bedrock of a rapid in the river.

Belonging to the flowering plant family Podostemaceae, the existence of this species was previously unknown to science. It has since been named as Ledermanniella yiben Cheek by Kew scientists.

Local botanists continued to search for further populations at the many river rapids across Sierra Leone and Guinea, but none have yet been found.

Rocky river with plants and trees.
Ledermanniella yiben is only known from a single rapid in the Seli River in Sierra Leone. The plants grow on bedrock and are submerged for most of the year; they flower and fruit in the dry season when the water levels are low.

Critically endangered

Growing in a colony, only at this single locality, the population at the Seli River would appear to represent the entire world population of this species.

These plants are naturally adapted to the river’s rising and falling water levels; they are submerged for most of the year becoming exposed and flowering at the end of the dry season.

However, this very habitat is at risk and this plant population will be submerged permanently when the construction of the proposed hydroelectric reservoir is implemented.

Therefore, Ledermanniella yiben was identified as a critically endangered species which could potentially become extinct in the very near future.

Bee on plant.
The flowers of Ledermanniella yiben are pollinated by bees.
Brown plant with moss-like appearance in running water.
Ledermanniella yiben is a flowering plant but looks like a lichen or a moss.

Conserving seeds

To prevent this species from possible extinction, Kew scientists collaborated with Njala University, Sierra Leone to conserve seeds at Kew’s Millennium Seed Bank (MSB) where they can survive for tens, hundreds, or even thousands of years.

However, the journey to the seed bank at Kew was not straightforward and involved several important steps:

  • Collecting: Once we received permission from the Sierra Leonean authorities, we collected the mature seeds from the population we found at Seli River. It is important to capture the genetic diversity without overharvesting seeds from an already threatened population.Of the 1000 mature plants growing in the area, we harvested seeds from 50 plants. The seeds are tiny (almost microscopic), oval and yellowish brown in colour. Part of the plant was sampled to prepare a dry specimen to store at the Kew herbarium as a future reference for plant identification. 
  • Arrival: The seed arrived at the MSB 18 days later and all accompanying documents were checked to ensure that seeds were collected and brought to the UK legally and that there was no risk of introducing pathogens and diseases. We then created a digital record on the Seed Bank Database including plant identification, geographic origin, habitat and population details. 
  • Drying and cleaning: Drying seeds to 15% relative humidity is the first and most important part in seed banking as it increases the lifespan of seeds. Once the seeds were dry, we removed as much non-seed material (debris) as possible.
  • Quality testing: Knowing the quality of collection is vital for curating. To estimate proportions of seeds which are viable and likely to germinate, a sample of seeds was cut open under the microscope using a scalpel blade. About 74% of the sample contained potentially viable seeds. Finally, the total number of seeds was estimated by weighing samples of seeds with known numbers. The seed collection weighed just over 10 grams but contained over one and a half million seeds. As the cut-tested seed sample contained about 74% of healthy seeds, the whole collection was estimated to contain over 1.24 million potentially viable seeds. 
  • Frozen world: Along with Kew’s 87,000 seed collections, the seeds of Ledermanniella yiben are now safely stored in the vault of the MSB within air-tight glass containers, ready to be used to grow new populations of the species for reintroduction in the years to come.
Four people kneeling on brown dusty rocks in Sierra Leone with buckets and clipboards
Collecting seeds of Critically Endangered Ledermanniella yiben, a member of the Podostemaceae family, in Sierra Leone © Xander van der Burgt/RBG Kew.
Small seeds.
Seed collection of Ledermanniella yiben.
Doors to storage room.
The Millennium Seed Bank's underground seed storage vault, which operates at -20°C.

Conservation implication

Seed banking remains a key part of Kew’s Science Strategy and Science Collection Strategy and contributes to Target 8 and Target 9 of the Global Strategy for Plant Conservation.

It promotes conservation by enabling the sustainable use of seeds in the seed bank for re-introduction of species, restoration of degraded habitats, research, education and display.

Kew and its scientists continue to safeguard plant diversity worldwide with a focus on plants most at risk and most useful for the future, while addressing global challenges for food security, sustainable energy, loss of biodiversity and climate change.

Thanks to

We thank the Government and Njala University of Sierra Leone, Joule Africa, and staff of the RBG Kew whose support has made the Millennium Seed Bank’s collections possible.


Cheek, M., van der Burgt, X., Momoh, J., & Lebbie, A. (2017) Ledermanniella yiben sp. nov. (Podostemaceae), Critically endangered at the proposed Yiben Reservoir, Sierra Leone. Kew Bulletin 72: 31. DOI 10.1007/S12225-017-9699-0. Available online

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