About six of the species in the Dahlia genus have been bred for cultivation as ornamental flowers. Wild species of dahlias have both disk and ray flowers in the flowering heads, but many varieties of ornamentals such as the common garden dahlia (D. bipinnata) have shortened ray flowers. The dahlia was first introduced into Great Britain from Spain in 1789, and countless varieties of dahlias, many of them double-flowered, were subsequently developed in Britain and elsewhere from the species D. variabilis and D. coccinea. The 2,000 horticultural varieties of dahlias are classed into 13 different types, including single, double, show, fancy, pompon, cactus, and peony-flowered dahlias. Dahlia flowers may be white, yellow, red, or purple in colour. Dahlias grow well in most garden soils. They flower late in the summer and do so until interrupted by frost in the autumn.