Aecial and telial host range, interfertility, teliospore dimensions, and amount of nuclear DNA were determined for Puccinia recondita collected either worldwide from species of cultivated wheats (Triticum aestivum and Triticum turgidum ssp. durum and rye (Secale cereale), or from wild emmer (Triticum turgidum ssp. dicoccoides) and four species of wild wheat (Aegilops) in Israel. The results indicate that the collections belong in two major groups: Group I (from cultivated wheats and wild emmer), which has Thalictrum speciosissimum (in the Ranunculaceae) as principal aecial host; and Group II (principally from wild wheats or rye), which has several species in the Boraginaceae, such as Anchusa aggregata, Anchusa italica, Echium glomeratum, and Lycopsis arvensis as aecial hosts. In glasshouse experiments, intercrosses could be made readily among collections within Groups I and II but not between the two groups. Group I consisted of all collections from Triticum aestivum, Triticum turgidum ssp. dicoccoides, and most collections from Triticum turgidum ssp. durum. For Group I collections, four species of Aegilops, Hordeum maritimum, S. cereale, as well as Triticum aestivum and Triticum turgidum ssp. durum and ssp. dicoccoides could all serve as telial host in glasshouse experiments. Group II consisted of four types, all clearly different from Group I. Type A was from Triticum turgidum ssp. durum found in fields near Anchusa italica, which was its only aecial host; Triticum aestivum, Triticum turgidum ssp. durum, and Triticum turgidum ssp. dicoccoides could serve as telial hosts. Type B was from Aegilops ovata and had E. glomeratum, Anchusa undulata, and L. arvensis as aecial hosts. Type C was from Aegilops longissima, Aegilops sharonensis, and Aegilops variabilis and had Anchusa aggregata, Anchusa undulata and L. arvensis as aecial hosts. Type D was from S. cereale and had L. arvensis and Anchusa undulata as aecial hosts. In addition to differences in host range, teliospores were wider and bigger in cross sectional area, and nuclear DNA content of pycniospores was 1.3–1.6 times greater in Group II than in Group I. The results suggest that Groups I and II have evolved separately for an extended period and are now morphologically distinct and genetically isolated from each other. Furthermore, differences in both telial and aecial host species, in teliospore dimensions, and in amount of nuclear DNA indicate that subgroups within Group II are beginning to show genetic divergence. Key words: aecial hosts, Aegilops, Anchusa, Echium, Hordeum, leaf rust, Lycopsis, Puccinia recondita, Puccinia triticina, Secale, Thalictrum, Triticum.