A new variety of Puccinia coronata causing a disease on barley and other gramineous species is described. The fungus is different from other reported forms of P. coronata in both morphology and pathogenicity. Its most prominent characters are the elongated teliospore appendages with dichotomous branching and wide pathogenicity on species in the tribe Triticeae, particularly the genus Hordeum. The name of P. coronata var. hordei is proposed for the rust fungus. The common name 'crown rust of barley' is proposed for the disease of barley caused by this rust fungus. Results of inoculation indicated that P. coronata var, hordei' is pathogenic on species of Aegilops, Agropyron, Elymus, Elytrigia, Leymus, Pascopyrum, Psathyostachys, Secale, and Triticum in the tribe Triticeae, and some species of Brachypodium, Bromus, Festuca, and Lolium in the tribe Poeae, and Phalaris in the tribe Aveneae. In the northern Great Plains of the USA, the following native and introduced gramineous species were found naturally infected by P. coronata var. hordei: Bromus tectorum, Elymus canadensis, E. trachycaulus, E. virginicus, Elytrigia intermedia, E. repens, Hordeum jubatum, H. vulgare, Leymus angustus, L. cinerius, L. dahuricus, L. racemosus, Pascopyrum smithii, Psathyrostachys juncea, and Secale cereale.
