Keeping invasive plants in check

By Linda Brandt

November 25, 201



As invasions of pythons, iguanas and monitor lizards make news, less sensational but equally threatening plant species are invading Florida, overtaking natural native plant communities on beaches and in wetlands, forests, prairies, preserves and even backyards. They disrupt natural water flow, enable fires to spread and accelerate the decline of endangered plant and animal species. Some of these invaders were introduced into the U.S. by people with the best of intentions. Others arrived unnoticed as stowaways in shipments from foreign countries. While invasive plants are not recommended for landscapes, they may already a part of yours. If so, there are ways of controlling and preventing them from "escaping" to native plant communities. Detailed instructions for preventive measures, as well as mechanical, chemical, cultural and biological controls of invasive plants, may be found at http://plants.ifas.ufl.edu/node/133. Environment-friendly replacements are suggested for the invasive plants discussed.

Air potato (Dioscorea bulbifera)

Commonly seen blanketing fences, power lines and trees, especially in shady residential areas. A native of tropical Asia, air potato was introduced to the U.S. by the USDA for agricultural purposes.

Look for ...

Vigorously twining vine up to 70 feet

Broad heart-shaped leaves with prominent veins

Aerial tubers (bulbils) resembling potatoes

Not to be confused with ...

Winged yam (Dioscorea alata), which has similar leaves but is much shorter and has fewer bulbils. Not as invasive as air potato, but toxic.

Environmental impact: Air potato may grow up to 8 inches per day, forming a dense canopy, blocking sunlight from native plants and providing a bridge for fire to spread. Placed on the Florida Noxious Weeds List in 1999.

Replacements: Moonflower vine (Ipomoea alba), Carolina jessamine (Gelsemium sempervirens)

Australian pine (Casuarina equisetifolia)

Not a true conifer, Australian pine was introduced to the Miami and Palm Beach areas from Australia in the 1890s to be used as windbreaks around canals, agricultural fields, roads and houses. By the 1990s, it had escaped into natural habitats of native plants.

Look for ...

Tall stands of swaying trees that seem to whisper or sigh in the wind

Evergreen, single-trunked tree growing to 150 feet

Brittle, peeling reddish brown to gray bark

Branchlets resembling pine needles

Clusters of small, conelike structures

Thick blanket of leaf litter allowing nothing else to grow under trees

Environmental impact: Because they are resistant to salt spray and can grow close to sea water, Australian pines have invaded thousands of acres of southeastern and southwestern Florida coastline. They displace native plant communities that provide habitat for threatened and endangered plant and animal species. They tend to topple in high winds and pose a significant hazard to coastal storm evacuation routes. Possession with intent to sell is illegal in Florida without a special permit.

Replacements: Longleaf pine (Pinus palustris), slash pine (Pinus elliottii), red cedar (Juniperus virginiana)

Brazilian pepper (Schinus terebinthifolius)

Green leaves and bright red berries made Brazilian pepper popular as a Christmas decoration at one time. The berries are believed by some to intoxicate migrating robins. Native to Brazil and Paraguay, Brazilian pepper was present in Florida as early as 1840 and was widely sold as a landscape ornamental in the 1920s.

Look for ...

Short trunk supporting a tangled mass of branches 15 to 30 feet high

Elliptic-oblong leaves with dark green upper surfaces

Peppery odor when leaves are crushed

Inconspicuous white flowers that produce bright red, berry-like clusters in late fall

Environmental impact: Dense thickets completely shade out and displace native vegetation and alter natural fire behavior. Because it is in the same family as poison ivy, sap may cause skin irritation and produce an acrid smoke when burned. Seeds are widely dispersed by raccoons, opossums and fruit-eating birds. It is the most widespread invasive plant species in Florida, occupying more than 700,000 acres. It may exude a chemical that inhibits the growth of native plants.

Replacements: Necklace pod (Sophora tomentosa), Dahoon holly (Ilex cassine), Walter's viburnum (Viburnum obovatum), Wax myrtle (Myrica cerifera)

Carrotwood (Cupaniopsis anacardioides)

Fast growth rate and ease of propagation made carrotwood popular as a landscape tree in the 1960s, but those same properties have enabled it to overtake native plant communities in 14 south Florida counties.

Look for ...

Single-trunked evergreen up to 33 feet tall

Dark gray outer bark, orange inner bark

Oblong, leathery, shiny yellowish green leaves 8 inches long and 3 inches wide.

Short woody capsules with three-ridged segments that turn from yellow-orange to brown, exposing three shiny oval seeds covered by a yellow-red crust

Environmental impact: Carrotwood invades beach dunes, marshes, tropical hammocks, pinelands, mangrove and cypress swamps, scrub habitats and coastal strands altering understory habitat.

Replacements: Wax myrtle (Myrica cerifera), Florida privet (Forestiera segregata), Gumbo-limbo (Bursera simaruba), Green buttonwood (Conocarpus erectus), Dahoon holly (Ilex cassine), Yaupon holly (Ilex vomitoria), Sweetbay magnolia (Magnolia virginiana)

Chinese tallow (Sapium sebiferum)

Grown in China as a seed-oil crop for about 1,500 years, Chinese tallow was introduced to the U.S. as a landscape plant in the 1700s. Some sources say it was introduced by Benjamin Franklin. It is also known as popcorn tree and Florida aspen.

Look for ...

Deciduous tree 33 to 52 feet tall with milky sap, which is toxic

Open fruit capsules resembling popcorn

Seeds with a white waxy coating

Oval, aspen-like leaves

Small yellow flowers on spikes 8 inches long

Environmental impact: Chinese tallow thrives in most soils and tends to colonize large areas. It is now widespread in Florida along roadside ditches, coastal areas and streams, often forming dense thickets. Its rapid growth and spread threaten aquatic and upland environments.

Replacements: black gum (Nyssa sylvatica var. biflora), red maple (Acer rubrum), persimmon (Diospyros virginiana), cedar elm (Ulmus crassifolia, Turkey oak (Quercus laevis, post oak (Quercus stellata)

Cogon grass (Imperata cylindrical)

This aggressive perennial grass entered the U.S. as orange crate packing in 1912. It was later intentionally introduced into Florida in the 1930s and '40s as a potential forage and soil stabilizing plant. It is on the Florida Noxious Weeds list, which prohibits new plantings.

Look for ...

Loose to compact bunches of leaves originating at ground level and reaching 1 to 4 feet

Light green leaves 1/2-to-3/4-inch wide that turn orange brown with age

Serrated leaf margins

Prominent off-center white mid-rib

Plume-like silky 8-inch panicles in spring

Environmental impact: Rhizomes penetrate 6 inches to 4 feet into soil and exude substances that inhibit growth of other plants. Cogon grass infests ditch banks, pastures, road sides/right-of-ways, golf courses and forests. Cogon grass thrives on fine sand to heavy clay, on soils of low fertility and in dry to moist natural areas. Dense stands of cogon grass result in almost total displacement of native plants that are important to wildlife. They also present a significant fire hazard on public conservation lands and agricultural forests.

Replacements: Eastern gamma/Fakahatchee grass (Tripsacum dactyloides), love grasses (Eragrostis elliottii or E. spectabilis)

Lantana (Lantana camara)

When well-controlled, this fast-growing deciduous shrub is a favorite for butterfly gardens. A more compact mounding variety is recently commercially available.

Look for ...

Square stems with bristly hairs or small prickles

Oval, hairy, aromatic leaves

Small multicolored (white to pink or lavender, yellow to orange or red) flowers in dense, flat-topped clusters

Round fleshy, 2-seeded fruit turning from green to purple or blue-black

Environmental impact: Invades disturbed sites, such as roadsides, pastures, citrus groves and cultivated woodlands. Also found in well-drained undisturbed habitats, such as native pinelands, hammocks, and beach dunes.

Melaleuca (Melaleuca quinquenervia)

Known also as punk or paper bark tree, melaleuca is valued in its native Australia by beekeepers and is even protected because it is attractive to birds and bats. It was introduced into Florida in 1906 as a potential commercial timber and later as a landscape ornamental tree and windbreak. It was also planted to dry up the Everglades to decrease mosquito populations and allow for development.

Look for ...

Papery, spongy, brownish-white bark that peels off in layers

Stiff, lance-shaped, 5-inch evergreen leaves

Spikes of creamy-white to pinkish flowers

Broadly cylindrical, woody seed capsules in clusters surrounding young stems

Environmental impact: This nonnative tree is rapidly displacing native cypress and sawgrass in the Everglades. It can flower five times per year. Any damage to the tree that cuts water flow to the stems containing seed capsules, such as fires, freezes and control techniques, will result in seed release. Seeds can remain viable for 10 years, and a single tree can store 2 million to 20 million seeds.

Dense stands displace native plants that are important to wildlife. Melaleuca forests are a serious fire hazard to surrounding developed areas because the oils contained within the leaves create hot crown fires. Melaleuca may grow 3 to 6 feet per year. Possession with the intent to sell or plant is illegal in Florida without a special permit.

Replacements: Pignut hickory (Carya glabra), Water hickory (Carya aquatica), In wetland areas: Pop ash (Fraxinus caroliniana), Sweetbay magnolia (Magnolia virginiana), In upland areas: Southern magnolia (Magnolia grandiflora)