petunia, any plant of the genus Petunia, South American herbs of the family Solanaceae (nightshade family). The common garden petunias, planted also in window boxes, are all considered hybrids of white-flowered and violet-flowered species from Argentina. The plants are of a straggling habit and produce an abundance of large, funnel-shaped, fragrant blossoms. Petunias are classified in the division Magnoliophyta, class Magnoliopsida, order Polemoniales, family Solanaceae.

Any of many species of flowering plants in the genus Petunia, in the nightshade family, which originated in South America. The innumerable varieties of showy, trumpet-shaped flowers are immensely popular. There are two types: the compact, erect sort seen in summer garden beds, and the sprawling, long-stemmed sort seen in hanging baskets and window boxes. From early summer until frost, petunias bloom profusely with single or double blossoms; crisped, fringed, or ruffled flowers; and spectacular hues from pure white to deep crimson or purple, speckled or veined in contrasting colours. Leaves are soft, flabby, and covered with fine, sticky hairs. Technically perennials, petunias are most often grown as annuals.

Learn more about petunia with a free trial on Britannica.com.