PlantFiles: Bulls-Horn Acacia
Acacia sphaerocephala

Do you know if the ants are agressive toward people and pets? I think the plant is beautiful and would consider getting one if it would survive in the winter ( I live in Boise, ID) and if my cat and dogs (both labs) wouldn't get terribly harmed by the ants if they got too close.
lisapb864

It's an easy plant to start from seed, since you scarify it. My seedlings are still a few centimeters high but they are doing quite well. The "bull horns" may injure distracted people, so be careful!

According to killerplants.com, Acacia sphaerocephala is one of the five species known as Bee Wattle or Bull's-horn Acacia. The interesting thing about these species is the "ant" relationship, which is mutualistic. Here's how it works: Pseudomyrmex ferruginea, the type of ant with these species, cannot survive without these trees; nor so can the tree or they fall victim to competition from other plants. One of the thorns is first colonized by a single queen ant, which chews a hole in the thorn near the tip. She lays 15 to 20 eggs eventually inside the thorn. Soon, as the colony starts to grow, the ants disperse and move to other thorns. The ant colony becomes agressive once the population of ants reaches around 400 members, and drive out other ant colonies and kill any insects foraging for food on the tree, to protect the tree. The ants act as caretakers for the tree, and clear the ground and keep it free of any other plants and even prune surrounding branches of other trees that threaten to outshade the acacia. Without the protection of the ant colony, the acacia tree would fall vulnerable to chewing insects such as beetles or caterpillars, and surrounding trees and shrubs would quickly outcompete the acacia without the maintnance work of the ants to keep the tree safe. The ants also recognize certain odors, such as when they become 'odor-sensitive' when humans or cattle are in the vincity of the tree, and the ants immeadiately swarm out to sting intruders if the tree is touched.

The relationship of the ants and the trees is really fascinating, besides the tree's spectacular appearance and interesting folklore that surrounds it.

According to the ISB Atlas of Florida Vascular Plants, this species is established and grows wild in the U.S. only in Miami-Dade and Collier counties in southern Florida.

Credits to killerplants.com and the ISB Atlas of Florida Vascular Plants and the Plants National Database.

To IslandJim - I searched out all this information by using Google.

This is one of those plants that are beyond curious. The "horns" have that polished white look more akin to ivory than long horn steer. I would recommend to anyone interested in this plant to search it out with Google. It's an "ant plant" and there is lots of interesting lore and anecdotal information about it on the web.