Why the iconic thorn trees of Africa are no longer called true acacias

Gardening · Published 3 October 2026 Swipe more like this →

In short: For centuries, the iconic thorn trees of the African savanna were known as acacias. But in 2009, a major taxonomic shift moved them into a new genus: Vachellia. This change was not just a label swap; it was the result of a heated, decade-long scientific battle over botanical naming rights.

The genus Vachellia belongs to the legume family, Fabaceae, and is defined by its capitate inflorescences and spinescent stipules. These trees and shrubs are famously well-armed, using modified stipules as spines to defend against herbivores like giraffes and gazelles. While they are often associated with the African landscape, where 83 of the 157 known species reside, they are found globally, with native populations spanning the Americas, Asia, and the Pacific.

The confusion surrounding their name stems from a 2005 decision by the General Committee of the International Botanical Congress. Taxonomists had determined that the broad genus Acacia needed to be split into at least five distinct groups. To prevent the renaming of nearly 920 Australian species, the committee opted to reassign the name 'Acacia' to a new type, effectively stripping the title from the African thorn trees. This move was deeply contentious; at the 2005 congress, 54.9% of representatives voted against the change, but because a 60% majority was required to override the committee, the decision stood.

The controversy persisted until the 2011 congress, where a vote of 373 to 172 officially upheld the earlier ruling. This solidified the separation, leaving the African species under the genus Vachellia. Despite the modern scientific consensus, the history of these plants runs deep. Long before the New World was discovered, Europeans in the Mediterranean were already familiar with Vachellia species, utilizing them for medicinal purposes and inheriting their names from the ancient Greeks and Romans.

Today, Vachellia remains a diverse and resilient genus. Its members exhibit complex physical traits, including bipinnate leaves and flowers that typically appear in spherical, yellow or creamy-white heads. Some species, such as V. tortilis and V. luederitzii, carry both spines and recurved prickles, a testament to the intense evolutionary pressure of their environments. As of June 2026, the genus encompasses 157 species, continuing a legacy that has fascinated botanists and travelers for millennia.

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