Mexican petunia, or ruellia brittoniana, is a perennial shrub that grows to be about three feet high and three feet wide and is not too hard to care for. This evergreen has dark green leaves that grow to between six and twelve inches long and to between half-an-inch and three-quarters-of-an-inch wide. Its leaves have prominent veins on their undersides, and its margins are smooth or wavy. The foliage appears almost metallic blue or purple under full sun.
The flowers on the ruellia brittoniana are trumpet-shaped, and between one-and-a-half and two inches in diameter. They are either solitary flowers or they're borne in clusters at the tips of the plant's purple stems. They can be white, pink, purple, or any shade of blue. These flowers bloom enthusiastically during the hottest part of the year. It grows faster than most other commercially available flowers.
The plant is native to Mexico, hence the name, but it can be found throughout the southeastern United States, invading habitats in places like Florida. It prefers fertile soil with significant moisture content. It can be grown indoors as a houseplant if it's given access to bright light. It works well as a houseplant because it is typically free of pests and diseases.
When it grows outside, it requires full sun or partial sun exposure. The more light the plant receives, the more it will bloom. It is characterized as requiring average to moist soil conditions; it becomes very aggressive when it is given access to an abundant water supply. Once established, however, it will survive dry spells.
However beautiful, the Mexican petunia is listed as a Category 1 invasive species by the Florida Exotic Pest Plant Council. It is so listed because it alters native plant communities by displacing native species. Regular management of yards and gardens will prevent the spread of the Mexican petunia; if you find yourself infested with this shrub, hand-pulling and removal of the entire plant is practical for small infestations.