The distribution ofElymus macouniiVasey in the Prairie Provinces of Canada is extensive and apparently governed by the occurrence of its putative parents,Agropyron trachycaulum(Link) Malte andHordeum jubatumL. The hybridE. macouniiwas produced by controlled cross-fertilization ofA. trachycaulumandH. jubatum. Subsequently, octoploidE. macouniiwas obtained by colchicine treatment. Cytological studies indicated 2n = 28 forA. trachycaulum, H.jubatum, andE. macounii(both artificially produced and naturally occurring hybrids). Irregular meiosis ofE. macouniiand some irregularity in meiosis of octoploidE. macouniiwere observed.