Here at Lake & Wetland Management, Inc., a core part of what we do is control the influx of invasive plant species into our waterways. Why is this important? Because these waterways’ health depends on the health of their vegetation. And their vegetation cannot derive the sunlight and nutrients they need if they are competing with invasive — and often exotic — species.
So what are the plants you should watch out for? Well, to answer this very question, we’re going to go over Florida’s 12 most invasive Category I species. Category I covers those plants that are so disruptive that they have either displaced or hybridized (merged species) with native plants — and therefore pose the largest threat to our aquatic vegetation.
Aquatic Soda Apple
Scientific Name: Solanum tampicense
Origin: From Mexico and/or the West Indies in the 1970s
The Aquatic soda apple, as it is known, inhabits the shorelines and shallow rivers of Central Florida. Coming to the Sunshine State from Mexico in the 1970s, this invasive plant represents an ecological threat because it can grow up to 15 feet tall and quickly take over entire monocultures (when a single plant inhabits an entire area). Because it is extremely difficult to disentangle its dense monocultures from native plants, the only option is to completely eradicate this invasive species.
Scientific Name: Salvinia molesta
Origin: South America
“Giant Salvinia” originates from South America, and it was likely introduced to Florida’s ecosystem by horticulturalists in the 1990s. Widely deemed one of the world’s worst weeds, this plant rapidly reproduces to form dense communities that not only reduce O2 levels in water (thereby killing fish), but also clog irrigation channels and block navigation for aquatic vessels.
Scientific Name: Hydrilla verticillata
Origin: Came from Asia in the 1950s
Hydrilla has been a statewide problem ever since it came to Florida from Southeast Asia as part of the 1950s’ aquarium trade. It produces millions of plants per acre and, because about 80% of its mass takes up the upper 2 ft. of water, it blocks sunlight and oxygen from aquatic wildlife and has also been known to reduce property values. Nevertheless, because it spreads by buds and fragments (it does not reproduce by seeds), it is classified as under “management control” rather than total eradication.
Scientific Name: Hygrophila polysperma
Origin: India & Malaysia
Like Hydrilla, Hygrophila is also the product of the Southeast Asian aquarium trade. After ming to Florida around the mid-1940s, it infested much of South and Central Florida’s canals and waterways by forming dense surface mats that monopolize sunlight and oxygen. It is particularly problematic in South Florida, but is notoriously difficult and expensive to control. Therefore, its management effort is based on complaints alone, and there is no statewide/institutional effort to stop its invasion.
Scientific Name: Pennisetum purpureum
This emergent grass came from the “Old World” at the dawn of the 20th century and quickly invaded South and Central Florida’s shorelines and soils. Forming dense, clumpy grasses that can grow up to 12 ft. tall, Napier Grass is especially problematic because it blocks canals and compromises flood control. Its deep roots make it resilient during droughts, but it can nevertheless be severely injured by freezing.
Scientific Name: Urochloa mutica
Origin: Pacific rim islands
Coming to the United States on slave ships, where it was used as bedding, para grass was introduced to Florida as early as the 1870s. It inhabits various wetlands, marshes and floodplains, but it is particularly prevalent in roadsides and other disturbed areas. Like Napier grass, it is sensitive to freezing, but the tropical climate of the Sunshine State offers a lack of solutions to stopping its invasion.
Scientific Name: Panicum repens
Origin: “Old World” (Europe and/or Africa)
One of the earliest exotic plants to invade Florida, torpedograss was introduced as a forage grass during the late 1800s. It inhabits an array of habitats statewide, ranging from dry land to six feet of water. Its thick mats make both water movement and navigation difficult, and it has a tendency to displace native plants wherever it grows. Due to its extensive and resilient rhizomes (rootstocks that send lateral roots and shoots from their nodes), it is extremely difficult to control, and management is undertaken on a complaint basis.
Scientific Name: Eichhornia crassipes
Origin: South America
This invasive plant is floating rather than emergent, and it was likely brought to Florida around the 1880s. It is officially a statewide problem, but it is particularly problematic in South Florida in the more peninsular wetlands. One of the most rapidly proliferating exotic plants (doubling in numbers in only 2 weeks), it is the cause of not only nutrient and navigation blockage, but also sedimentation and mosquito infestation.
Scientific Name: Pistia stratiotes
Origin: South America
Water lettuce originates from South America and likely came on ship ballasts during the colonial period. It floats along water surfaces mostly in the Floridian peninsula (rather than the panhandle) and displays growth rates similar to the water hyacinth. Like the water hyacinth, it also harbors mosquitoes and prevents both air and light diffusion into water.
Scientific Name: Ipomoea aquatica
Origin: Mid-1900s from China
The emergent “water spinach” is a peculiar plant that likely came as a vegetable crop from China. It inhabits sites that range from dry land to shorelines to floating mats, and its infestation occurrences are isolated sites that span the whole state. It can grow up to 7 inches per day and form dense canopies that block nutrients, and is currently under FWC eradication.
West Indian Marsh Grass
Scientific Name: Hymenachne amplexicaulis
Origin: Central and/or South America, West Indies
Coming to Florida from tropical habitats, West Indian marsh grass began invading the shallow waters of South and Southwest Florida in the 1970s. It can form dense monocultures in wetlands and shorelines, and its resilience during volatile weather periods causes it to displace native grasses. Difficult to control due to its growth among native species, this invasive plant species is currently under maintenance control.
Scientific Name: Colocasia esculenta
Origin: India and Southeast Asia
Wild Taro came to Florida in the early 1900s — likely as a food crop — and now inhabits wet soils and floating islands that are statewide in scope. It has a tendency to displace native species along shorelines and wetlands, and at 60% it is one of the most widely dispersed invasive species in Florida’s waters. Because its patter is to break loose from shoreline infestations and form floating islands, the management effort policy is limited to the eradication of new colonies and floating islands.