The St Helena Olive Tree (\(Nesiota elliptica\)) is a significant example of modern plant extinction. This small, unassuming tree was a unique biological treasure that evolved in complete isolation on the remote volcanic island of St Helena in the South Atlantic Ocean. Its fate illustrates the fragility of island ecosystems when faced with the pressures of human colonization.
The Endemic Nature of the St Helena Olive
\(Nesiota elliptica\) was a monotypic species, meaning it was the only plant in its genus and found nowhere else in the world. It was restricted to the high-altitude cloud forest and tree fern thicket ecosystems on the eastern central ridge of St Helena, particularly around Diana’s Peak. The tree was a small, stout, and low-spreading shrubby tree, typically reaching about five meters in height with prolific branching.
Its appearance was distinctive, featuring dark-colored wood and oblong leaves that measured between 50 and 70 millimeters, often curling outwards at the edges. The dark green leaves had a pale underside covered in fine hairs, giving the tree a deep gray appearance. From June to October, the tree produced small, dense clusters of pink flowers, followed by hard, woody seed capsules containing triangular seeds. Despite its common name, the species was not related to the true olive (\(Olea europaea\)), but belonged to the Rhamnaceae family.
Factors Driving the Rapid Decline
The decline of the St Helena Olive began with the arrival of humans on the island in the early 16th century. Early settlers caused extensive deforestation to clear land for plantations and harvest native wood for timber. This destruction eliminated the moist, high-altitude cloud forest habitat where the St Helena Olive thrived.
The introduction of non-native species compounded this pressure. Feral goats grazed heavily, devouring young shoots and preventing natural regeneration of the olive and other native flora. Invasive plant species also outcompeted the specialized native vegetation, degrading the remaining habitat. Furthermore, the tree harbored an inherent biological vulnerability: it was highly self-incompatible. This reproductive mechanism, which encourages genetic diversity in a large population, became a severe liability when only a few genetically similar individuals remained.
The Final Stand: Last Known Specimen and Extinction
The species was considered lost for a time in the 19th century, until a single wild specimen was discovered in August 1977 by George Benjamin on a steep cliff face near Diana’s Peak. This lone survivor represented the entire wild population, making its conservation an immediate priority for scientists. Teams attempted artificial propagation by taking cuttings, but the inherent self-incompatibility mechanism made generating new seedlings extremely difficult.
The last known wild St Helena Olive succumbed to its weakened state and was found dead on October 11, 1994, leading to the species’ classification as Extinct in the Wild. The species persisted for a few more years in cultivation through a small number of propagated cuttings and seedlings. The final cultivated specimen, which had been the sole surviving plant since 1999, was housed at a nursery but struggled with persistent health issues. This last tree finally died in December 2003, having succumbed to fungal infections and termite infestation, declaring \(Nesiota elliptica\) globally extinct.
Continuing the Legacy: Post-Extinction Searches and Hybrids
Following the loss of the last cultivated specimen in 2003, the genus \(Nesiota\) became extinct. However, scientists had the foresight to collect and store genetic material from the tree before its final demise. A DNA sample is now preserved in the Kew Gardens DNA bank, ensuring that the tree’s unique evolutionary information is not erased and potentially making it a candidate for future de-extinction research.
Furthermore, the extinction serves as a catalyst for ongoing conservation efforts focused on the remaining endemic flora of St Helena. Conservationists continue working to restore the cloud forest ecosystem, hoping to prevent other unique species from meeting the same end. The search for any overlooked wild individuals in remote or inaccessible ravines of the island continues, though the chances of finding a survivor are considered remote. The empty space left by the St Helena Olive, sometimes symbolically represented by an empty pot in a botanical garden, underscores the permanent absence created by extinction.