The Bullhorn Acacia

By Susana Cortázar

The acacia cornigera/bullhorn acacia tree, found at Zoo Miami’s warthog paddock and along the fence next to the Guanaco exhibit, is quite interesting. Native to Mexico and Central America, it is called “bullhorn” because of its swollen thorns found in pairs at the base of its leaves, which resemble a bull’s horns.

A unique feature of this tree is that colonies of stinging ants make their home in the hollowed-out thorns and are true defenders of the tree – fending off insects, curious mammals and epiphytic vines! Why does this happen? Because the bullhorn acacia lacks alkaloids normally found on the leaves of other trees which act as a deterrent to insect and other animal infestation. In the case of the bullhorn acacia, the ants “take over the job” of the alkaloids. In return – mutualism – the bullhorn acacia provides the ants with protein lipids, which are found as little white spots on the acacia’s leaves, and nutrition in the form of a nectar rich in carbohydrates from glands on the tree’s leaf stalk.

According to tree expert Bob Beck, “if you get too close to the thorns of the bullhorn acacia or accidentally rub against one, you can do some serious scratching and even rip open your skin. The thorns are that pointy, sharp and strong! And the fact that the tree grows to 33 feet in height makes it a heavyweight. So steer clear when you come across them!”

Other interesting facts about the bullhorn acacia, aside from providing food and shelter for the ants, is that the tree’s thorns are sometimes strung together to make necklaces and belts. In some Central American countries, the thorns are used to make the legs for small ballerina dolls which are worn as pins by the locals.

Medicinal uses are attributed to this tree as well. Snake doctors use its bark and root to slow down snake venom as it enters the bloodstream; water extract from the thorns is said to cure acne and other skin problems; and most interesting, it is used to treat male impotence!

Photos by Bob Beck