Sally Scalera: Beware of these beautiful invasive plants; they're not good for Florida
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Gardening is a fun hobby because there are so many great plants to grow.
We grow plants for the food they produce, their fragrant flowers, for their colorful foliage and for many other reasons.
Then there are plants that are recognized as invasive, and the plant that I have in mind is still for sale in the garden centers, even though it has been on the Category I list of the Florida Exotic Pest Plant Council for more than15 years. The plant I want to warn you about is called Mexican petunia, originally Ruellia brittoniana and now Ruellia simplex.
First, let me explain the difference between invasive plants and aggressive plants.
Florida native plants such as elderberries can become aggressive in disturbed areas, but because they are native, they don’t disturb the ecosystem, and they support our native insects and wildlife.
Plants that produce berries, like the non-native Brazilian pepper tree, are spread by birds, and over time can move large distances. When non-native, or exotic plants, move into natural areas, they can create monocultures, crowding out the native species.
Just last year, I learned how harmful the invasive plants are to our natural areas and yards. I watched the webinar, A Guide to Restoring the Little Things that Run the World, presented by Doug Tallamy and hosted by the Florida Wildflower Foundation.
The gist is that insects are at the base of the terrestrial food web, and insect populations are already at dangerously low levels. Supporting both our migratory and local birds, plus our native bees, is crucial and the large presence of invasive exotic plants in wild areas and yards is fueling this problem.
Mexican petunia, Ruellia simplex, is a tough plant that produces beautiful purple flowers but be warned, it can spread all over your landscape and beyond. Mexican petunia was brought to Florida in the 1940s and identified as a Category I invasive exotic by the Florida Exotic Pest Plant Council in 2001.
Category I plants are the most damaging because they displace native plants, alter the ecosystem, change ecological functions and hybridize (cross pollinate) with native species. The UF/IFAS Assessment of the Status of Non-Native Plants in Florida’s Natural Areas has determined that Mexican petunia is invasive in north, central and south Florida.
For everyone who has Mexican petunia in their yard, it’s important to remove them as soon as you can. Your job won’t be over after their removal, though, because you will need to remain vigilant for the appearance of new plants.
Continually remove them as soon as you discover them and be prepared to do that for more than a year.
If you really love the Mexican petunia, there is good news. The sterile "Purple Showers" cultivar doesn’t produce viable seeds and can be planted. Other sterile cultivars developed at UF are “Mayan Purple,” “Mayan White” and “Mayan Pink.”
Don’t be fooled by the cultivars “Chi Chi,” (pink-flowered), “Snow White” (white-flowered) and the dwarf cultivars in the “Katies” series (that come in purple, pink and white), because they all produce viable seed and are also considered invasive.
If you want to grow dwarf plants, grow our only native in this genus, Carolina wild petunia, Ruellia caroliniensis.
Examples of non-native plants that have hybridized (cross-pollinated) with native plants are Lantana and Porterweed.
Lantana camara has become naturalized throughout Florida and can be found growing at the base of fence posts, in open fields, etc.
There are three native lantana species that can be found in Florida.
Hammock lantana, Lantana canescens, is a bushy shrub that produces very small heads of yellow-centered white flowers. This species is found in Miami-Dade County along the hammock margins.
The native wild sage, L. involucrate, is an upright, bushy shrub that produces white flowers with yellow centers that often have a violet blush. This species is found in central and southern counties.
Our last native species, L. depressa, is endemic to Florida, is on the endangered list, produces yellow flowers, and has three distinctive varieties that vary by the locations where they are found.
The native variety that is found in Brevard County is Lantana depressa var. floridana.
The invasive lantana, L. camara, is easy to recognize because it produces brightly colored pink and yellow or orange and yellow flowers in the same inflorescence.
This species of lantana is also very poisonous to both humans and cattle, and deaths have been reported here in Florida. The unripe, green fruits are fatal when eaten.
The foliage can also cause acute liver problems if eaten by dogs.
Lantana camara has not only naturalized throughout the state, but it has also contaminated the gene pool of all three of our native Lantana depressa varieties. The EPPC considers the Lantana camara cultivars "Gold Mound," "New Gold," "Alba" and "Partiot" to be sterile.
The UF/IFAS Assessment of Non-native Plants also recognizes "Bloomify Red" and "Bloomify Rose" as “not a problem species.”
I previously mentioned porterweed as another example of a non-native plant cross-pollinating with a Florida native.
Our native blue porterweed, Stachytarpheta jamaicensis, is a low-growing groundcover that reaches a mature height of 1 foot. We also have Stachytarpheta urticifolia, a non-native woody shrub that grows to a height of 4-6 feet, that can be found throughout the state.
When these two species cross pollinate, their seedlings are called S. x intercedens, and it appears that they have math skills, because their mature height is right in the middle at 2-3 feet.
I would be willing to bet that the least favorite gardening activity is weeding so, why add a plant that could run amuck throughout your yard, neighborhood, and possibly the state?
The next time you go to the garden center, pass on the Mexican petunia (which has naturalized throughout Florida, plus in six other southern states, Hawaii, Puerto Rico, and the Virgin Islands) and let your family, friends and neighbors know about its bad habits also.
If you are curious about what other plants are invasive, check out the EPPC’s website at fleppc.org and make plans to eradicate any that you find growing in your yard.
Sally Scalera is an urban horticulture agent and master gardener coordinator for the University of Florida’s Institute of Food and Agriculture Sciences. Email sasc@ufl.edu.
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