Dahlia 'Bristol Stripe' flowers. This USA variety is classified as a decorative dinnerplate dahlia. The blossom measures 10 to 15 centimetres across. Dahlias were one of the species that Darwin pointed out for the diversity of the variations selectively bred for the floral trade. He theorized that if man could create varieties from a single species then it would happen naturally through evolution. Photographed in Mulhouse, France, in autumn.