A case of mistaken identity: Isotropis iophyta (Fabaceae), a new Western Australian Lamb’s Poison previously confused with I. forrestii

Abstract

Several species of ‘Lamb’s Poison’ (Isotropis Benth.: Mirbelieae, Fabaceae) have been reported as toxic to stock including I. forrestii F.Muell. (Bennetts 1935; Gardner & Bennetts 1952, 1956; Gardiner & Royce 1967; Cooper et al. 1986). According to Gardiner and Royce (1967: 512) ‘...in mid-October 1966, studies were made of I. forrestii, ingestion of which had just caused the death of 10 cattle on a station near Wiluna in the East Murchison division. Seeds of the variety were found in the rumen contents, and extracts of the plant produced acute death and typical renal damage in guinea-pigs’. Cooper et al. (1986) went on to demonstrate nephrotoxicity in sheep using dried and milled I. forrestii obtained from the Western Australian Department of Agriculture, noting that this material was originally collected from a Meekatharra farm after an outbreak of Isotropis poisoning in sheep. The toxic compound that caused the renal failure was subsequently extracted, found to be novel, and named Iforrestine (Colegate et al. 1989).