Bioassay-guided fractionation of the methanol extract of the root bark of Solanum arundo Mattei led to the isolation of a steroidal glycoalkaloid, designated arudonine, which was elucidated to be solasodine O-alpha-l-rhamnopyranosyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3)], [alpha-l-rhamnopyranosyl-(1-->4)]-beta-D-glucopyranoside. This steroidal glycoalkaloid inhibited the growth of lettuce seedlings (Lactuca sativa).