Nitro Compounds in Indigofera Species1

Abstract

The genus Indigofera consists of approximately 700 species of tropical and subtropical origin. Several of these species are being investigated for possible introduction into the southern United States. Leaves of Indigofera species grown in the field and greenhouse, or sampled from herbarium specimens, were analyzed colorimetrically for aliphatic nitro compounds. Aliphatic nitro compounds were found in 64 of 250 species of Indigofera in concentrations of 2 to 12 mg NO₂/g of plant. Four species that assayed 4 to 12 mg NO₂/g were moderately toxic to 1‐week‐old chicks when administered as an aqueous extract. Hairy indigo (Indigofera hirsuta L.), a commercial variety already introduced, did not contain nitro compounds and was nontoxic to chicks. Indigofera species proposed for introduction into the United States should be examined for the presence and concentration of nitro compounds.