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Exotic Vegetation

What is an exotic plant?

An exotic plant is a plant that has been introduced to an area outside its native range. Often, when people come to visit or settle in Florida, they purposefully bring seeds of their favorite plants with them from other places. Other times, exotic species are transported accidentally, where seeds or pieces of a vegetatively reproducing plant are unknowingly attached to cars, boats, or even hiking boot shoes. Many of these exotic species thrive Florida's subtropical climate, with warm weather, infrequent freezes, and plentiful rain. Over time, if the introduced species cultivate and grow wild in Florida, they are considered to be naturalized species.

Are all exotic plants a problem?

Not all exotic species cause a problem. In fact, most naturalized species live in Florida without causing significant damage. However, some exotic species do not have natural competition in Florida. As a result, they grow rapidly, taking over natural vegetation and disrupting the habitat and food sources for native wildlife. Florida spends millions of dollars combating invasive vegetation each year.

Florida's invasive exotic wetland plants

The following wetland pest plants are included on the Florida Exotic Pest Plant Council's (FEPPC) 2003 List of Invasive Species.

Click on the common name for more information and pictures of each species from the University of Florida's Center for Aquatic and Invasive Plants.

(Note: information on each species was summarized from the Langeland/Burks book, Identification & Biology of Non-Native Plants in Florida's Natural Areas)

Casuarina equisetifolia
Since the early 1900s, these evergreen trees have been planted extensively across south Florida coastal dunes as windbreak and shade trees. Australian pines are salt tolerant and can grow in the front-line dunes, displacing native plants with rapid growth, dense shade, and dense litter accumulation. They produce a chemical that inhibits growth of nearby native plants. They reproduce prolifically, with as many as 300,000 seeds per pound, and spread rapidly, with seeds dispersed by birds, water and wind.

Suckering Australian-pine
Casuarina glauca
Similar to Casuarina equisetifolia, this tree was planted across southern Florida coasts as a windbreak, roadside tree and hedge. It suckers aggressively from spreading roots, creating dense jungle of branches that excludes other vegetation. It tends to completely take over areas where it becomes establish. This false pine colonizes nutrient-poor soils easily by nitrogen fixing microbial associations.

Wild taro
Colocasia esculenta
This perennial herb was introduced to Florida in 1910 by the U.S. Department of Agriculture as a crop substitute for potatoes. Today, the crop is widely naturalized along streams, marshy shores, canals and ditches, and has been found in 235 public water bodies.

Columbrina asiatica
Believed to have been brought to Jamaica in the 1850s from East Asia for use as a medicine, food, fish poison and soap substitute, this evergreen shrub became naturalized in the Florida Keys and Everglades by the 1930s. It takes over native vegetation by entangling stems several feet deep, growing over and shading out even trees. It grows in many disturbed and undisturbed sites, including Florida's coastal hammocks and the Keys, where it threatens a number of rare, listed native plant species. Stems of the shrub can grow up to 32 feet in a single year. The plant forms adventitious roots where branches touch the ground, and it vigorously resprouts from cut or injured stems. Seeds are buoyant and salt-tolerant, making long-distance dispersal possible.

Eichhornia crassipes
This floating aquatic herb occupied 126,000 acres of Florida land by 1950. It grows at explosive rates exceeding any other tested vascular plant and can double its population in as little as 8 to 16 days. It creates dense mats on the water's surface, degrading water quality and dramatically altering native plant and animal communities. It reproduces both vegetative, from stem tips underneath water surface, and sexually.

Hydrilla, water thyme
Hydrilla verticillata
In 1994, this submersed, usually rooted, aquatic perennial herb invaded more than 40 percent of Florida's water bodies. It creates dense stands that alter fish populations, cause shifts in zooplankton communities and affects water chemistry. The herb can produce up to 6,000 tubers and 3,000 turions per m2, aiding its rapid dispersal and growth.

Eastern Indian hygrophila. Image from the South Florida Water Management District.East Indian hygrophila
Hygrophila polsperma
This perennial aquatic herb is replacing hydrilla as the most series weed in south Florida canals. It grows rapidly, with the ability to expand its population 100-fold in one year. Easily developing new stands from rooted nodes of even small fragments, its spread is difficult to control. It forms dense monoculture stands with stem tips submersed up to 10 feet deep and can photosynthesize in lower light than most native submersed species. Grows most vigorously in flowing water.

West Indian marsh grass
Hymenachne amplexicaulis
This dominant perennial grass species is replacing maidencane marshes in the Myakka River basin, at Ringling MacArthur tract in Sarasota County, Mountain Lake in Hernando County, and Fisheating Creek, near Lake Okeechobee. It easily adapts to fluctuating water levels, and can persist after long periods of drought or up to 40 weeks of flooding. It produces seeds prolifically.

Melaleuca trees. Image courtesy of the South Florida Water Management District.Melaleuca
Melaleuca quinquenervia
Scattered over the Everglades in the 1930s to create forests and dry up the swampland, this grows extremely fast, producing dense stand s that displace native vegetation and reduce native wildlife habitat and food. In 1994, it infested an estimated 490,000 acres in south Florida, especially Loxahatchee Slough, Big Cypress Swamp and the Everglades. While regional control efforts have reduced its coverage, it is recognized by the United Nations as a threat to the Everglades. It produces up to 20 million windborne seeds per tree per year and can hold the seeds for massive, all at once releases in stressed conditions. Also, Melaleuca releases oils in the air, especially in blooming season that may cause respiratory irritation, asthma attacks, headaches or rashes.

Silk reed
Neyraudia reynaudiana
This robust reed-like perennial is colonizes marginal and undisturbed habitats. It is well established in the rock pineland habitats of Dade County, where it is viewed as a threat to rare native species. It is highly flammable and has been linked to fires outside Everglades National Park.

Skunk vine
Paederia foetida
Introduced by the U.S. Department of Agriculture before 1897 as a fiber crop, this perennial twining vine has invaded tree gaps and disturbed areas across Florida. It creates dense canopies leading to damage or death of native vegetation, adapting quickly to changes in light, soil and salt conditions. This vine has is destroyed the few remaining paths of the endangered Cooley's water willow.

Torpedo grass
Panicum repens
This sturdy perennial grass is considered one of the most serious grass weeds. In addition to infesting citrus groves and golf courses across the state, it was found in 70% of Florida's waters by 1992, displacing 14,000 acres of native marsh. It rapidly reproduces by rhizome extension and fragmentation and is stimulated by tilling and fertilization of soil. Each year, Florida spends an estimated $2 million a year for to manage the weed in flood control systems.

Napier grass
Pennisetum purpureum
This perennial grass has been reported as a weed in 29 Florida counties and in 24 other countries around the world. It grows in dense reed patches, preventing regeneration of native species. It can dominate fire-adapted savanna communities and is often found in scrub, pine rockland, hammocks, sinks, lake shores, swamps and prairie habitats. In the past, this grass has created flood control problems by blocking runoff's access to canals, reducing water flows and overgrowing pump stations. Mechanical control is not an effective removal for this weed, because it can easily resprout from leftover rhizomes.

Water lettuce. Image courtesy of the South Florida Water Management District.Water lettuce
Pistia stratiotes
Forming extensive mats this floating herb disrupts submersed plant and animal communities, and interferes with water flow and navigation. This plant may have been brought by humans as early as 1565 and occurred in 128 state water bodies by 1989. Today, statewide management programs have reduced the plant's abundance by half. Still the plant is considered highly invasive, producing up to 1,000 rosettes per m2 in South Florida. Water lettuce also serves as a host for at least 2 genera of mosquitoes.

Chinese tallow tree
Sapium sebiferum
This deciduous tree grows up to 52ft tall, and is used in the U.S. as an ornamental tree and potential oil crop species. It has expended its range along the Gulf Coast in low-lying areas, becoming dominant and spreading along roadside ditches to wet soil areas. It also tends to take over large areas in well-drained areas near human habitation in undisturbed areas like closed canopy forests, bottomland hardwood forests, waterbody shores and even floating islands.

Brazilian pepper
Schinus terebinthifolius
In 1997, this evergreen shrub or small tree is estimated have invaded 700,000 acres in central and south Florida. It forms tangled thickets of woody stems, shading out and displacing native vegetation in fallow farmland, pineland, hardwood hammocks, roadsides and mangroves forests habitats. The tree produces allelopathic chemicals in the soil which suppress the growth of other plants. It also produces chemicals in leaves, flowers and fruits that irritate human skin and respiratory passages.

Wetland nightshade
Solanum tampicense
Forming large, tangled, single-species stands, this sprawling prickly shurb was prefers undisturbed wetland sites, typically invaded cypress swamps and river margins. It can clamber over native vegetation, dominate the understory of cypress heads, and grow over and cover even large plants. It reproduces successfully, forming adventitious roots at leaf axils and producing seeds that are viable for at least 12 months, showing 90% germination on fresh seeds.

Seaside mahoe. Image courtesy of the South Florida Water Management District.Seaside mahoe
Thespesia populnea
This evergreen shrubby tree spreads its lower branches to create impenetrable thickets and large fruit crops. It is commonly found on coastal areas of south Florida and the Keys, especially in mangrove communities and low-wave action beaches where its growth is adapted to the salt spray and high winds. The tree thrives in low silty land and coral and sand berms, and can shift into a more efficient photosynthesis process (C4-type) under high saline conditions.

Green-, or white-flowered wandering Jew
Tradescantia fluminensis
This creeping branches perennial herb commonly forms dense single-species ground covers that smoother native species. These herb blankets can be up to 2 feet deep in overlapping leafy stems. The wandering Jew is most commonly found in moist to wet hammock areas, well-drained woodlands and shady residential yards. Though the plant is commonly cultivated as a house or patio plant it is difficult to control once established.

Pará grass
Urochloa mutica
Considered one of the world's worst weed and reported as an agricultural pest in 34 countries, this perennial grass forms from widely creeping stolons. It's high productivity, fast growth and allelopathic abilities (the grass releaseschemicals into the soil to kill nearby plants) make it an aggressive plant creating single-species stands. Today, it invades disturbed low areas like canals, and displaces native vegetation along river and lake shoreline and in marshes and swamps. In 1986 it was found in 52% of Florida's water bodies, but today's coverage has dropped.


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