Dahlia is a genus of bushy, tuberous, herbaceous perennial plants native to Mexico and Central America. They are grown as annuals in some regions with cold winters. There are 42 species of dahlia, with hybrids commonly grown as garden plants.
Dahlia hortensis is a member of the Asteraceae family of dicotyledonous plants, its garden relatives thus include the sunflower, daisy, chrysanthemum, and zinnia. Flower forms of the plant 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) ("dinner plate"). The stems are leafy, ranging in height from as low as 30 cm (12 in) to more than 1.8–2.4 m (6–8 ft). The majority of species do not produce scented flowers. The dahlia was declared the national flower of Mexico in 1963. The tubers were grown as a food crop by the Aztecs, but this use largely died out after the Spanish Conquest. Attempts to introduce the tubers as a food crop in Europe were unsuccessful.