In vitro induction of polyploids using colchicine causes an increase in DNA content in plants. This is of high importance especially for plants that have medicinal and commercial values. Seeds of two medicinal plants, licorice Glycyrrhiza glabra L. var.glandulifera and safflower Carthamus tinctorius were treated with different concentrations of colchicine, 0%, 0.03%, 0.05%, 0.08%, 0.1% (W/V) in vitro for 24 and 48 h. Treated seeds then were cultured on solid Murashige and Skoog (MS) media under controlled conditions. After a month, the length of the stomata was measured to study the effect of colchicine on stomata size. Cellular DNA content of the regenerated plants was measured by spectrophotometry. Flow cytometry was used for confirming the results obtained from stomata size measurement and spectrophotometry. Results suggested that treated plants have a fair amount of larger stomata, significantly in licorice plantlets that were treated with 0.1% colchicine for 24 h and safflower plantlets that were treated with 0.03%, 0.05% and 0.1% colchicine. Safflower DNA content in all treatments enhanced significantly, but in licorice only DNA content of plantlets that were treated with 0.05% colchicine for 24 h and 0.1%, 0.03% colchicine for 48 h found to be increased significantly. The morphological features of treated plantlets such as shoot and leaf thickness were found to be increased. Flow cytometry confirmed the previously mentioned results and suggested tetraploids in all treated safflower plantlets and licorice plantlets obtained from treatment with 0.08% of colchicine and mixoploids in licorice plantlets obtained from treatment with 0.1% of colchicine. ª 2015 Production and hosting by Elsevier B.V. on behalf