Vachellia cornigera aka Bullhorn Acacia

Vachellia cornigera is a shrub or small tree in the pea family, Fabaceae. Its common names include bull horn thorn and bull horn acacia. Older sources call it Acacia cornigera. Its native range runs from Mexico into Central America. Records include Guatemala, Honduras, and Costa Rica. Kew places it in the seasonally dry tropics. It grows in both damp and dry sites within this range.

The tree can reach about 33 feet [10 metres]. Some wild plants reach 49 feet [15 metres]. Another source entry gives a height of 26 feet [8 metres]. These figures describe the species, rather than a clear garden range. It grows in thickets and open woodland, chiefly on plains. It can form dense stands. It also grows beside rivers and in swampy ground. Records extend to about 2,950 feet [900 metres] above sea level. Other sites include old fields, grazing land, and roadsides.

Hollow thorns give this tree a close link with ants. The ants live inside the thorns and defend their host. They attack animals that browse the tree or pose other threats. The tree feeds them through its leafstalks and leaflet tips. This partnership matters when handling a plant that houses ants. Its roots also support helpful bacteria in small nodules. These bacteria capture nitrogen from the air. The tree uses some of that nitrogen. Nearby plants may also gain from this process.

People gather the ripe pods from wild trees for food. In some places, sellers take large harvests to local markets. The edible portion is the pulp around the seeds. Pods measure about 0.13–0.16 feet [0.04–0.05 metres] long. They are about 0.05 feet [0.015 metres] thick. The hollow thorns also serve a craft use. Makers use them as patterned elements in beaded necklaces.

Seed propagation needs work because the seed coat blocks water. Scarify the coat, then soak seeds in warm water for 24 hours. The source gives about 21°C as the best germination temperature. Even treated seeds may germinate poorly. Sprouting takes about 30–50 days. Plants develop a deep taproot and dislike root disturbance. Move young plants to their final site early. Semi-ripe side shoots also provide material for cuttings.