Bull's-Horn Acacia (Acacia sphaerocephala): The Ant-Plant with Swollen Thorns

Bull's-Horn Acacia (Acacia sphaerocephala) is a fascinating myrmecophyte—an "ant-plant" that has evolved a mutualistic relationship with stinging ants. Its most striking feature: pairs of huge, inflated, hollow thorns at each node, resembling bull horns, which house ant colonies.

Symbiotic Wonder

The ants live inside the swollen thorns and feed on nectar from extrafloral nectaries and protein-rich Beltian bodies on leaflet tips. In return, they aggressively defend the tree from herbivores and clear competing vegetation. This classic symbiosis is a textbook example of coevolution.

Botanical Profile

• Family: Mimosaceae
• Genus: Acacia
• Species: sphaerocephala

Growth & Ecology

A small, fast-growing tree to 15–25 feet with feathery, bipinnate leaves and yellow pom-pom flowers. Native to dry forests of Central America. In cultivation, it needs full sun, excellent drainage, and frost-free conditions. Without its ant partners, it's vulnerable to browsing. A conversation piece for tropical collections and ecological gardens.