Mexican Petunia: Buyer Beware

Mexican Petunia (Ruellia simplex) is ubiquitous in Florida. The handsome dark green foliage topped with purple trumpet-shaped flowers made it a favored landscape plant through much of the 20th century, and you'll see large swathes of it today in gardens, surrounding mailboxes, in parking lot medians... pretty much everywhere. It's fast-growing, drought-tolerant, and available at any big-box store nursery. What's not to love?

Quite a bit, actually. As it turns out, Mexican Petunia has its insidious side. The same factors that make this plant easy to grow also make it incredibly invasive in the landscape. Rooting it out can be nearly impossible. Florida gardeners can tell you: be careful where you plant Mexican Petunia, because once you put it in, you'll probably have it forever. The Florida Exotic Pest Plant Council classifies this as a Category I invasive, which means it is "altering native plant communities by displacing native species, changing community structures or ecological functions, or hybridizing with natives."

Mexican Petunia is a perennial in zones 8 - 11, which includes all of Florida. It spreads in two ways: seeds and rhizomes. Fertile varieties of Mexican Petunia set seed capsules that explode when ripe, sending seeds flying several feet from the plants. The seeds themselves are sticky when first released, so they can adhere to passing wildlife and be spread even further. Mexican Petunia also establishes massive underground root systems, and new shoots spread up as the rhizomes extend until you have a huge mass of Mexican Petunia that overtakes an area and is extremely difficult to remove.

In recent years, some sterile cultivars of Mexican Petunia have been created that do not set seed. The popular cultivar 'Purple Showers' is one such example, along with 'Mayan Pink' and 'Mayan White', which have pink and white flowers, respectively. However, these cultivars still spread underground, so while they're somewhat less invasive, they can still become a problem pretty quickly.

Mexican Petunia does have some value for wildlife. Bees enjoy visiting this plant, though they have to climb pretty deep inside to find the pollen. Some butterflies are able to feed on the blooms, though it requires a fairly long proboscis to reach the nectar (sulphurs are especially known to enjoy these flowers). And a few butterfly species can use it as a host plant, including the Common Buckeye (Junonia coenia), White Peacock (Anartia jatrophae), and Malachite (Siproeta stelenes). However, it's important to note that while the caterpillars of these species can eat these plants, they are unlikely to actually lay eggs on them. So don't plant Mexican Petunia expecting to attract these butterfly species - it's not going to work.

If you have a major problem with Mexican Petunia, there are some ways to tackle it. It generally means getting a shovel and digging up as much of the root system as you can find - not a fun job. Herbicides can also be used, but only with great caution. Get more info on fighting Mexican Petunia from the University of Florida IFAS Extension by clicking here. (Incidentally, Florida has a great native wild petunia, Ruellia caroliniensis. It's easy to find at native plant nurseries and deserves a place in any Florida-Friendly garden.)

What's in a Name? As you might guess from the name, Mexican Petunia is native to Mexico, as well as South America. Though it has the common name "petunia", it's not closely related to the common garden petunia of the genus Petunia.  It has had a variety of scientific names, including Ruellia brittoniana and R. tweediana, but in recent years botanists have returned to the original nomenclature of Ruellia simplex. Ruellia is in honor of French physician and botanist Jean Ruel, while simplex refers to the simple (rather than compound) leaves of the plant.