Leptosphaeria biglobosa n.sp. is described for the weakly virulent (or non-aggressive) pathogen causing blackleg of oilseed rape and canola. The new species differs from the aggressive blackleg organism, Leptosphaeria maculans (Desm.) Ces. & De Not. in having a very prominent beak on the ascomata that is greatly enlarged at the apex. Ascomata of both species were produced on canola stems either by inoculation of compatible strains of the Phoma anamorph or by single ascospore isolates at a distance of 1 cm and letting them grow together. Both species exhibit bipolar heterothallism. Interspecific crosses were negative. In a study of type specimens of Leptosphaeria species with 5-septate ascospores infecting Cruciferae, none were found that matched the features of L. biglobosa. Leptosphaeria napi (Fuckel) Saccardo on Brassica napus L., and Leptosphaeria virginica (Cooke & Ellis) Saccardo on Lepidium virginica L., are synonyms of L. maculans. Leptosphaeria submaculans Holm on Sisymbrium, Berteroa, and Erysimum has distinctively enlarged ascospores. Leptosphaeria alliariae (Desm.) Ces. & De Not. on Alliaria officinalis Andrz., has much smaller ascospores. Leptosphaeria lindquistii Frezzi on Helianthus annuus L. of the Asteraceae has ascospores with only one, two, or rarely, three septa but was considered because it too has a Phoma anamorph.Key words: Phoma lingam, B group, ascomata.