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Chromosomes were studied in somatic cells of 60 plants of blue grama, Bouteloua gracilis (Willd. ex Kunth) Lag ex Griffiths, collected from a 7-hectare field of native range at the Central Plains Experiment Range (CPER), Nunn, Colorado, to determine chromosome constitution in relation to the plant characteristics. Somatic chromosomes were studied in root tips collected from vigorously growing plants in the greenhouse. Acetocarmine squash method was used to make slide preparation. The majority of the plants were 2n =40. However, three plants were 2n=50 and two were 2n=60. The pentaploid plants (2n =50) were recorded for the first time in this report. Additional 94 plants collected from entire CPER were all 2n =40. The basic chromosome number of blue grama was determined to be x=10. There was no significant relation between chromosome number and morphological traits: culm height and number, basal diameter, and plant dry weight.