Which toxic tree species is commonly known as black locust?

The toxic tree species commonly known as black locust is Robinia pseudoacacia.

Robinia pseudoacacia is a deciduous hardwood in the legume family, Fabaceae, native to parts of the eastern United States. It has been planted widely beyond its native range and can become invasive because it spreads through underground suckers. Its fragrant flower clusters, durable wood, and ability to enrich soil through nitrogen fixation have made it valuable in forestry, landscaping, and beekeeping.

The toxicity is concentrated in parts such as the bark, leaves, and seeds. Important toxic constituents include lectins, especially the toxalbumin commonly called robin. Horses and other livestock that consume the plant may develop digestive and neurological signs, including colic, weakness, depression, or cardiac abnormalities.

“False acacia” is another common name and reflects the species name pseudoacacia, meaning false acacia. Black locust is not a true Acacia; the two groups are only superficially similar. It is also easy to confuse black locust with honey locust, but black locust has shorter paired prickles at leaf bases rather than honey locust's large branched thorns.