Dahlia is a genus of bushy, tuberous, herbaceous perennial plants native to Mexico. A member of the Asteraceae or Compositae, dicotyledonous plants, related species include the sunflower, daisy, chrysanthemum, and zinnia. Flower forms are variable, with one head per stem; these can be as small as 5 cm 2 in diameter or up to 30 cm 1 ft or about the size of a dinner plate. The dahlia was declared the national flower of Mexico in 1963. The tubers were grown as a food crop by the Aztecs.