Cross-inoculations to leek and onion plants using isolates of Cladosporium from leaf blotches on leeks or onions showed that no cross-infection occurred between isolates and their respective hosts. The species causing leaf blotch on leeks was morphologically distinct from that causing a similar disease on onions and the differences, augmented by the results obtained from the cross-pathogenicity tests, indicate that two taxa should be recognized at the rank of species. Following an examination of type or authentic material it was concluded that the name C. allii (Ell. & G. W. Martin) P. M. Kirk & Crompton comb. nov. should apply to the species causing leaf blotch on leeks and C. allii–cepae (Ranojevi) M. B. Ellis to that on onions.