Ruella brittoniana is native to Mexico, but is now wildly dispersed through the Southeast United States. In Florida, where it is a perennial, it is considered an invasive plant. Since it is only hardy thru zone 8, it is an annual in Missouri. Commonly known as Mexican Petunia. The genus name honors Jean de la Ruella (1474-1537) a French herbalist. Ruella brittoniana is called Mexican Petunia, but it is not even related to petunias.

Ruella is a member of the Acanthaceae.  The lance-shaped leaves are deep green to 15–30 cm in length and 1–2 cm wide. Stems are strong, semi woody, reaching about 1 meter tall.

Blooms are a vibrant purplish blue, trumpet shaped, and 3-5 cm. The flowers are borne on the tips of the stems. Each bloom lasts only one day, but the succession of non-stop blooms makes it a very showy plant.

Varieties with white, pink, and many shades of blue are available, as are dwarf versions that form clumps that are about 20–25 cm in height. Mexican petunia is very showy when in full bloom due to the clouds of admiring butterflies that swarm about the plants. Ruellia is essentially disease and pest free, so it’s very environmentally friendly. Even better, hummingbirds, butterflies and bumblebees love this plant!

Culture: Prefers fertile soil with moisture, but is very adaptable. Ruellia brittoniana  tolerates high heat, is drought tolerant, and can endure high humidity. Mexican Petunia prefers full sun, but will tolerate shade (it just doesn’t flower as profusely). After flowering, cut back stems about halfway for a new crop.  Ruellia brittoniana  is an easy to grow plant with strikingly colored flowers that is seldom bothered by disease or pests. It blooms enthusiastically throughout the hottest time of the year. Propagation is very easy. Clumps can be divided; stem cuttings easily root in moist soil or sand; and seeds often self sow.

The use in landscape: Ruellia brittoniana prefers sun to part shade. The quantity of blossoms is related to the amount of light the plant receives. The more direct sunlight the more flowers with fewer flowers appearing in overcast conditions or when grown in shadier conditions.
Mexican Petunia prefers average to moist soil. It is a water plant that becomes very aggressive with access to abundant moisture. Survives dry spells once established. Mexican petunia can be grown indoors as a houseplant in bright light. When growing Mexican Petunia indoors water freely when in active growth but water only when dry in winter.