zinnia, any species of the genus Zinnia of the family Asteraceae (aster family), native chiefly to Mexico, though some range as far north as Colorado and as far south as Guatemala. The common zinnia of gardens (Z. elegans), called also youth-and-old-age, is a rather coarse, easily cultivated annual, popular as a cut flower for its warm colors—ranging from white and yellow to red and purple—and for its bold, stiff aspect. There are various forms in cultivation, including dwarfed, curled, and double varieties. The zinnia is the state flower of Indiana. Zinnias are classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae.

Any of about 22 species of herbaceous plants and shrubs that make up the genus Zinnia (composite family), native mainly to North America. Where native, they are perennial; elsewhere they are annual. Zinnias have stiff, hairy stems and oval or lance-shaped leaves arranged opposite each other and often clasping the stem. The numerous garden varieties grown for their showy, solitary flowers come from the species Z. elegans. Garden zinnias range from dwarf compact plants (less than 1 ft, or 30 cm, tall), with flowers 1 in. (2.5 cm) in diameter, to giant forms (up to 3 ft, or 1 m, tall), with flowers up to 6 in. (15 cm) across.

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