Britton's Wild Petunia Ruellia simplex

Mexican petunia is an ornamental herbaceous perennial of the Acanthaceae family. It is shrubby with a woody base and somewhat aggressive. The plant typically grows to 3 to 4 feet tall in the wild, but only to 2 or 3 feet tall in gardens. It has linear, dark green leaves that may be tinged with purple, and measure 6 to 12 inches long and 0.75 inches wide. The flowers are petunia-like, lavender to violet, and only last one day. It is hardy in zones 8 through 10 and is evergreen in warm climates. It is an excellent annual flowering plant in colder climates.

This plant is native to Central and South America and the Caribbean. Mexican petunia plants will spread by rhizomes and self-seeding in the garden and have aggressively naturalized in South Carolina, Texas, and Hawaii. Although this plant has excellent flowering attributes, this species is currently listed as a Category One invasive species by the Florida Exotic Pest Plant Council (FEPPC) because it has been found to invade natural areas and displace native flora in the State of Florida.

The genus name, Ruellia, honors a French herbalist and physician, Jean de la Ruelle. The epithet, simplex, references its simple leaves. There has been confusion over the correct epithet, and it has had several different names over the years. Ruellia simplex is preferred since that was the original name given when it was first described in Cuba in 1870.

Mexican petunia prefers medium to wet soil that is fertile, well-drained, and flowers best in full sun.  Mexican petunia is a tolerant plant. It is willing to grow in boggy wet conditions, in soil that varies from wet to dry, and tolerates high heat and humidity. Once established, the plant does well in drought conditions. It is seldom damaged by deer. 

Cut back stems after flowering to encourage new flowers. They are easily propagated by cuttings, division, and seed. Keep in mind that some cultivars are sterile ('Purple Showers'), in which case they may be spread by rhizomes.

Mexican Petunia is very popular and may be grown in bog gardens, on the margins of ponds, and in beds and borders. It may also be used as a container plant on patios or as a houseplant. The vibrant colored flowers make this an attractive plant that is tolerant of a variety of urban conditions. Just remember that this plant reseeds easily, and removal may prove challenging from the home landscape.

Seasons of Interest:

Bloom:  Summer and Fall    Foliage:  Summer, Fall, and Winter in warm climates

Quick ID Hints:

• 3- to 4-foot-tall herbaceous perennial with green or purple stems
• lance-shaped, glossy, green leaves
• petunia-like lavender flowers, blooming summer through the fall
• fruits are bean-like pods that contain 4 to 28 seeds

Insects, Diseases, and Other Plant Problems: Mexican Petunia has no serious insect or disease problems; however, it can be difficult to eradicate once it is established. The plant's self-seeding and rhizomes contribute to its aggressiveness. The seeds are explosively expelled from their capsules and can persist in the soil.

VIDEO created by Andy Pulte for “Landscape Plant Identification, Taxonomy and Morphology” a plant identification course offered by the Department of Plant Sciences, University of Tennessee.