Invasive Exotic Plants

What defines an invasive exotic plant? Taking one word at a time:

Wild taro (Colocasia esculenta) with its heart-shaped
leaves and wedelia (Sphagneticola trilobata) with its cute
yellow daisy-like flower heads are both invasive exotics.
· Exotic – the plant was not found in Florida before the first Europeans arrived.

· Invasive – the plant takes over the landscape.

So the definition becomes a plant that is not native to Florida that grows and reproduces aggressively.

Examples of invasive exotic animal species are the python, which is taking over in the Florida Everglades, and the fire ant, which we all know and respect. An example of an invasive exotic plant species is the Chinese tallow tree, brought here because of its high oil content. Its cultivation spread because of its natural beauty and spectacular fall color and is now extremely invasive in Southern forests and wet prairies. A common garden flower, the Mexican Petunia, is also an invasive exotic. It’s hard to comprehend how something so beautiful could be so treacherous. Here in Highland Lakes, we have been working to eradicate invasive exotic Cogon Grass and Primrose Willow from our lakes and marshes.

Many of the introduced, exotic plant species were selected because of their beauty and their resistance to the chewing and sucking insects found here. This resistance gives the exotic species a selective advantage over the native plants. Most of the time, individuals, organizations and even local governments who contribute to the problem are ignorant of the facts that surround invasive plants.

Additionally confusing, is that invasive plants that are not in a certain extremely invasive category are not illegal to sell or to plant, example: Mexican Petunia. Invasive plants may have beautiful blooms and provide limited food for some wildlife, but they can be destructive to Florida’s native ecosystems.

Growing coral honeysuckle (Lonicera sempervirens)
attracts hummingbirds, which also eat lots of bugs.
We all love to feed the birds. A little-known fact is that all birds, even the seed-eating Cardinals and the nectar-sipping Hummingbirds require insects as a source of protein to feed their growing chicks. Without protein from insects, the chicks will not grow nor thrive. Without insects there will be no birds.

Florida-native trees and wildflowers support a whole host of chewing and sucking insects. And it is a good thing they do. The insects which native plants support are, in turn, eaten by other, larger creatures such as spiders, frogs, anoles and birds. Without the insects at the bottom of the food chain, the charismatic wildlife at the top of the food chain would have nothing to eat. Consider adding at least one Florida native wildflower to your Highland Lakes landscape to help our local bird and wildlife population.

So, to summarize, invasive exotics alter native plant communities by displacing native species, providing little or no food for native wildlife and changing plant community structures and ecological functions.

For an excellent article about the history of invasive plants in the Southeast, go to the American Nurseryman magazine, October 2010 issue, page 20.

Peg Lindsay


Anonymous said…
Peg, this is an excellent article. We were due to have something like this on our blog! I would like to clarify a few things. Exotic, simply means non-native, and can be applied anywhere in the world. You are right, in Florida, exotic plants are those that arrived by human means after the year 1492 (when Columbus landed in the Western Hemisphere). Since then, it is possible for a plant to arrive naturally, without human intervention, but botanists will often have a tussle about it (e.g. Oeceoclades maculata). An example of birds arriving after europeans are cattle egrets (which I believe first arrived in the 1950's?), which followed a similar path as Oeceoclades did, although they occur in different habitats. As far as I know, there is no eradication program for Cattle Egrets, although I do not know whether birders consider them "native". Invasive is a word often thrown around, even for natives! I prefer a definition of Invasive as "An exotic plant which spreads into natural areas". When a native plant "takes over" the landscape, as some can, I generally use the term "Aggressive" with my clients(even though we all know that plants do not have emotions). To make things even more complicated, it is possible for a plant to be native to one region of Florida, and invade into another region due to human influence (e.g. West Indian Mahogany, native to the upper Florida Keys and the southern tip of Florida, invading natural areas from landscaped material in Lee & Palm Beach counties, where it never occurred before 1492. We all must be careful to plant the right native in the right place too!--Steve W.
Rick Brown said…
Good article on the focus we all need on invasive species. Skunk Vine and is taking over and this 'stinker' is sure to get people focused on invasives. People are confused about Mexican Petunias and this article will help them understand about the beautiful sterile, Florida Friendly hybrid 'Purple Showers' is being planted everywhere as compared to the wild type introduced early in the last century and continues to be spread by seed attached to birds and wildlife.
Rick Brown said…
It takes time, money and persistence and lots of herbicides to defeat invasive species and there is not much hope against some like Cogon Grass with few natural enemies in their native land. Here is some hopeful news on the Skunk Vine front.
Excellent point regarding ignorance of flora, habitats, & the environment...too many designers remain "behind the curve," when considering native plants, and I truly hope this post finds a large audience! Thank you for a poignant piece with specific examples.

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