The Bromus ciliatus L. complex consists of diploids and tetraploids from throughout North America with considerable morphological variation. To determine levels of variability we have sampled 32 populations of this complex from eastern and western Canada, California, and Arizona. Important morphological characters that vary within this complex are pubescence (presence/absence and density) on the basal sheaths, nodes, and lemmas, and glume length. Morphological and cytological data from these populations and from herbarium specimens suggest that at least three groups are involved. One group (B. ciliatus sensu stricto) from throughout the range of the complex seems to consist of diploid individuals. Another group (B. richardsonii Link) consists of tetraploid individuals occurring in the Rocky Mountains from Alaska to southern California with isolated populations found in the Cypress Hills of southern Saskatchewan and Alberta. A peculiar combination of characters seems to distinguish a third group that is sympatric with the other two groups in Arizona and New Mexico. A detailed molecular characterization using RAPD markers to determine genomic relationships and genetic diversity within this complex has yielded valuable information. A discriminate analysis of all available characters will be presented.

Key words: Bromeae, Bromus, cytology, molecular genetics, morphology, Poaceae