Five lignans, five neolignans, two sesquilignans, and a dilignan were identified from a phytotoxic extract of Brassica fruticulosa L. Compounds 8, 9, 12, and 13 have been isolated for the first time. Structures were determined on the basis of their spectroscopic features. Their effects on the germination and growth of two dicotyledons, Lactuca sativa (lettuce) and Lycopersicon esculentum (tomato), and a monocotyledon, Allium cepa (onion), as standard target species have been studied.