Robinia species: Black Locust

Family

Fabaceae

Common Names

Black locust, false acacia.

Plant Description

Native to North America, Robinia is a genus of about 20 species of deciduous, perennial, shrubs and trees attaining heights of 80 feet (24m). The plants spread by suckering and by seed. Trunks are erect, bark gray and deeply grooved, young branches having a pair of spines at each node. Leaves once pinnately compound, 7 - 20 oval leaflets, turning yellow in the fall. Inflorescences are pendulous racemes from leaf axils. The showy pea-like flowers have 5 fused sepals, 5 petals with banner, and are white in color and fragrant.

The fruits are straight leguminous pods containing up to 10 brown kidney-shaped seeds.

Robinia neomexicana, and R. viscosa have pink flowers, and have been used in making showy pink flowered hybrids such as "Idaho locust" (R. pseudoacacia x R. viscose) (Fig. 344, Fig. 345 and Fig. 346).

Figure 344. Robinia "Idaho".

Figure 345. Robinia "Idaho" flowers.

Figure 346. Robinia pseudoacacia flowers.

Toxic Principle and Mechanism of Action

Various glycoprotein lectins (toxalbumins) such as robin, and the glucoside robitin have been isolated from the bark and seeds [1]. The specific mechanism of action of the lectins has not been defined but is presumed similar to the lectins ricin and abrin found in castor bean (Ricinus communis) and Abrus precatorius. Inhibition of protein synthesis and gastrointestinal irritation appear to be the main effects of the toxins.

All animal species are susceptible to poisoning including humans, horses, dogs, cats, cattle, poultry, and budgerigars [1-4].

Risk Assessment

Black locust and its hybrids are often planted for their showy flowers and their drought tolerance. Poisoning of household pets is unlikely, but the trees are a potential risk for livestock and especially horses that chew on the tree’s bark out of boredom.

Clinical Signs

Animals eating the bark or seeds of Robinia species exhibit gastrointestinal irritation and cardiovascular abnormalities. Vomiting, colic, diarrhea, dehydration, weakness, mydriasis, signs of shock, and cardiac dysrhythmias are commonly seen [4]. Fatalities are uncommon, especially if the animal is treated symptomatically for dehydration and shock. Activated charcoal orally may be helpful in reducing the effects of the lectins, and intravenous fluids and electrolytes should be administered until the animal’s gastrointestinal tract has recovered.