Eleven populations of five Avena species were analysed for meiotic characters including chiasma frequency and distribution as well as chromosomal association and segregation. Plants of a single population of A. eriantha showed the presence of 2n = 14 (diploid) and 2n = 4x = 28 chromosome number. Populations of A. barbata and A. wiestii possessed n = 14, while populations of A. sterilis ssp. ludoviciana possessed 2n = 6x = 42 (hexaploid) chromosome number. Tetraploid and hexaploid species showed diplontic behavior and formed only bivalents. The species and populations studied differed significantly in the frequency of chiasmata. B-chromosomes occurred in some of the species studied. Cytomixis and chromosome elimination led to aneuploid and unreduced pollen mother cell formation in the species studied.