The flowering plants called dahlias grow wild in Central America and Mexico. The Aztecs cultivated them, and Spanish explorers brought them to Europe. Dahlias form a genus of the family Asteraceae. Thousands of varieties have been developed from hybrids of Dahlia pinnata and D. coccinea. The flower was named for Anders Dahl, a Swedish botanist.
The flowers of wild dahlias are flat, with a yellow center and eight single scarlet rays. Those of modern varieties may be globe-shaped and double, or with many petals. Their color may be white, yellow, orange, red, or purple. The plants grow from 18 inches to 20 feet (46 centimeters to 6 meters) high. They bloom in late summer or autumn.
Dahlias may be grown from seed or cuttings, by grafting (to perpetuate rare varieties), or by division of the tuberous roots. Amateur gardeners commonly use the last method. After frost kills the tops, the tubers should be divided and then stored in a cellar.