Acacia cornigera, commonly known as Bullhorn Acacia (family Fabaceae), is a swollen-thorn acacia native to Mexico and Central America. The common name of "bullhorn" refers to the large, enlarged, hollowed-out swollen thorns (technically called stipular spines) that occur in pairs at the base of leaves, and resemble the horns of a steer. In Yucatán (one region where the bullhorn acacia thrives) it is called "subín", in Panamá the locals call them "cachito" (little horn) . The tree grows to a height of 10m.
The ants act as a defense mechanism for the tree, protecting it against harmful insects, animals or humans that may come into contact with it. The ants live in the hollowed-out thorns for which the tree is named. In return, the tree supplies the ants with protein-lipid nodules called Beltian bodies from its leaflet tips and carbohydrate-rich nectar from glands on its leaf stalk. These Beltian bodies have no known function other than to provide food for the symbiotic ants. The aggressive ants release an alarm pheromone and rush out of their thorn "barracks" in great numbers.
According to Daniel Janzen (Costa Rican Natural History, 1983), livestock can apparently smell the pheromone and avoid these acacias day and night. Getting stung in the mouth and tongue is an effective deterrent to browsing on the tender foliage. In addition to protecting A. conigera from leaf-cutting ants and other unwanted herbivores, the ants also clear away invasive seedlings around the base of the tree that might overgrow it and block out vital sunlight.
It is used to treat impotency in males.