Petunia is a genus of approximately 20 species of flowering plants in the family Solanaceae (nightshade family), order Solanales, native to South America. The genus belongs to the subfamily Petunioideae, which distinguishes it from other well-known members of Solanaceae such as tobacco (subfamily Nicotianoideae) and the tomato, potato, and pepper (subfamily Solanoideae).
Plants in the genus are tender perennials, typically producing funnel-shaped, tubular flowers in a wide range of colors. Most species are diploid with 14 chromosomes and are interfertile with one another as well as with the closely related genus Calibrachoa. Some botanists include Calibrachoa within Petunia, though this treatment is not universally accepted. The hybrid genus Petchoa has been derived from crossing Calibrachoa with Petunia.
The vast majority of petunias grown in gardens are hybrids, principally Petunia × atkinsiana (also known as Petunia × hybrida), which offers an exceptionally wide range of flower colors, sizes, and growth habits. In 2023, the USDA approved the sale of a genetically engineered bioluminescent cultivar called ‘Firefly’, a white-flowered Petunia hybrida that glows in the dark owing to inserted genes derived from a bioluminescent mushroom.
Ecologically, petunias are primarily insect-pollinated. A notable exception is Petunia exserta, a rare red-flowered species pollinated by hummingbirds. The tubular flower form also attracts certain Lepidoptera, including the Hummingbird hawk moth.
Etymology
The name Petunia derives from the French word pétun, meaning ‘tobacco’, which was itself borrowed from petyma, a word for tobacco in a Tupi–Guaraní language of South America. The connection reflects the genus’s close botanical relationship to tobacco within the family Solanaceae.
Distribution
Petunia is native to South America, where the approximately 20 wild species occur across a range of habitats. Garden petunias, which are predominantly hybrids, are now cultivated worldwide in temperate and subtropical regions.
Ecology
Petunias are primarily insect-pollinated. The exception is Petunia exserta, a rare red-flowered species adapted for hummingbird pollination. The tubular floral architecture is also favored by certain Lepidoptera, including the Hummingbird hawk moth (Macroglossum stellatarum). Most species are diploid with 14 chromosomes and are interfertile with each other and with Calibrachoa.
Cultivation
Petunias tolerate relatively harsh conditions and hot climates but are frost-tender. They require at least five hours of direct sunlight per day and grow best in moist, well-drained soil under conditions of low atmospheric humidity. Most varieties are best started from seed. In the ground, watering once a week is generally sufficient; containers and hanging baskets require more frequent irrigation. Growth peaks in late spring. Monthly or weekly fertilizing, depending on variety, promotes vigorous growth.
Taxonomy Notes
Petunia belongs to the family Solanaceae, subfamily Petunioideae, order Solanales. The placement of the genus Calibrachoa within or outside Petunia remains a point of disagreement among botanists. When treated as distinct, Petchoa — a hybrid genus derived from crossing Calibrachoa × Petunia — represents an intermediate group recognized by some authorities.
