Illegal and Invasive Plants

Texas Law

Control of Prohibited Plants

Prohibited Plant Species

Links to Other Sites

The spread of exotic plants in some state waters have chocked water ways and rendered portions of lakes unusable for humans and native aquatic life. Many of these plants are invasive, that is, they spread aggressively, outcompeting the native species. Some species form floating mats that impede boating, fishing, swimming and clog water intakes for irrigation and electrical generation. Thick mats also reduce oxygen content and degrade water quality for fish and other aquatic organisms.

Why do we as pond keepers need to be aware of these plants? Many infestations in the wild are the result of plants that have escaped cultivation in water gardens or aquariums. Retailers sell prohibited plants in defience of state or federal law. Hobbyists collect prohibited plants, either deliberately or accidentally, from the wild or by trading with other hobbyists. Improper disposal of prohibited plants can cause them to be introduced to local watersheds.

The spread of exotic plants is an extreme threat to the native aquatic environment and a potentially dangerous situation.

Texas Law

The State of Texas doesn't just frown on the possesion of harmful or potentially harmful exotic plants. It is illegal to posses these plants in Texas. Possession of any prohibited plant species is a Class B Parks and Wildlife Code Misdemeanor punishable by Each individual plant of a prohibited species constitutes a separate violation. The law applies to everyone: aquatic plant producers and distributors, garden centers, pond supply stores, pet stores, and individual pondkeepers. So if Joe Ponder is caught with 10 water hyacinth in his backyard pond, that would be 10 separate violations, with potential fines totalling $20,000.

For the complete list of prohibited and restricted plants and fish, you can download the official Revised Exotic Species Rules published by the Texas Department of Fisheries. This is a Word document.

Download Revised Exotic Species Rules now!

Control of Prohibited Plants

Plants on the prohibited list can be disposed of either by drying them out or by treatment with an heribcide. Remove the plants from the pond and place them on the sidewalk or driveway and allow them to dry out completely. Do not rinse them into the storm sewer. If you want to use an herbicide to treat a large pond, check the Links below for information on which herbicides are effective and how to apply them safely. There are also links to sites detailing biological controls such as the Triploid Grass Carp and the Milfoil Weevil.

To report prohibited plants sitings either in the wild, under cultivation, or for sale by retailers or wholesalers, call Texas Parks and Wildlife at 409-384-9965 or the Nonindigenous Aquatic Species Toll Free Hotline at 1-877-STOP-ANS .

Prohibited Plant Species

Common Name Family Species
Giant Duckweed Lemnaceae Spirodela oligorhiza
Salvinia Salviniaceae all species of genus Salvinia
Water Hyacinth Pontederiaceae Eichhornia crassipes
Water Lettuce Araceae Pistis stratiotes
Hydrilla (Florida Elodea) Hydrocharitaceae Hydrilla verticillata
Lagarosiphon (African Elodea) Hydrocharitaceae Lagarosiphon major
Eurasian Watermilfoil Haloragaceae Myriophyllum spicatum
Alligatorweed Amaranthaceae Alternanthera philoxeroides
Rooted Water Hyacinth Pontederiaceae Eichhornia azurea
Paperbark Myrtaceae Melaleuca quinquenervia
Torpedograss Gramineae Panicum repens
Water Spinach Convovulaceae Ipomoea aquatica
Federally Prohibited
Giant Salvinia Salviniaceae Molesta spp.

Giant Duckweed
Spirodela oligorhiza

Giant Duckweed is also called duck-meat, large duckweed, or common duckmeat.

Leaves are in groups of 2-5 or more; they are small (0.08-0.2 inch), flattened and rounded, and float at the surface with two or more filament-like roots dangling below. Leaves have 5-11 prominent nerves, and are green above and reddish below.

Giant duckweed is one of the largest of several types of duckweed. It floats on small ponds and quiet backwaters of bayous and streams. In small ponds giant duckweed may produce dense growths that may block light need by more desirable aquatic plants. It may produce growths thick enough to block access by wildlife and livestock.

See Also

Salvinia, Giant Salvinia
all species of genus Salvinia, Molesta spp.

Salvinia, also called Water Fern, is a small, aquatic fern that floats at the surface with a hairy root-like leaf dangling below. Floating leaves are in pairs, oblong to nearly round, about 0.4 to 0.8 inches in length. A third leaf is position below the water surface in place of roots. Floating leaves are bluish-green and covered with stiff hairs and bump-like projections. A crease usually runs down the center of each leaf. Giant Salvinia, S. molesta, has leaves 0.5 to 1.5 inches long. The leaves of young plants lie flat on the water surface; as the plants mature and form mats, the leaves are folded and compressed into upright chains. Giant Salvinia also differs from common salvinia, in having rows of cylindrical hairs on each leaf that are topped with 4 branches that arejoined at the tips to form a cage, giving the leaf a velvety appearance and allowing it to repel water. Common salvinia has leaf hairs that are not joined at the tips.

Salvinias are found in fertile, quiet-water areas in ponds and bayous. Giant Salvinia has caused severe economic and ecological problems in many countries including New Zealand, Austrailia and South Africa. Texas is aggressively working to eradicate Giant Salvinia.

See also

Water Hyacinth, Rooted Water Hyacinth
Eichhornia crassipes, Eichhornia azurea

Water Hyacinth has soooth-edged leaves of dark green which project above the water surface. Feathery roots dangle below or are rooted into the substrate. Floating Water Hyacinth has nearly circular or elliptical leaves that are up to 8 inches long. Flowers occur in spikes and are violet-blue with yellow markings. Rooted Water Hyacinth is very similar but lacks the inflated leaf stems and has smaller leaves (2 to 6 inches long) that tend to be more pointed. Flowers are similar to floating water hyacinth but are often less robust and more blue in color.

Water hyacinth is often sold for use in ornamental ponds. It can also be used as a component of animal feeds and for natural agricultural fertilization. It has recently been found to absorb a variety of toxins and heavy metals and has come into use for water purification. Water hyacinth is prohibited in Texas, and although exemptions for use in water purification have been incorporated into the Texas Parks & Wildlife regulations, exemptions are not likely to be granted for ornamental ponds.

See Also

Water Lettuce
Pistis stratiotes

Water Lettuce is also called Water Bonnet.

The leaves of Water Lettuce are 4 to 8 inches in length and have a velvety surface thanks to very small, hair-like structures covering the leaf surface. Leaves generally have a smooth edge and form rosettes resembling a head of lettuce. Leaves have approximately 10 distinct veins radiating outward from the narrowed leaf base and are spongy to facilitate buoyancy. Several plants may be connected along a comon axis (stolen). Roots dangle below and are feather-like, but unbranched. Flowers are very small and in the center of the rosette.

Water Lettuce floats on quiet ponds, lakes and bayous. It prefers soft, acid waters and is cold sensitive. It is occasionally sold in the pet trade. Water Lettuce can completely cover ponds, bays and small lakes blocking access and shading out more desirable aquatic plant species.

Aquarium plants sold as water lettuce are more likely to be broad-leafed water sprite, Geratopteris sp. (unrestricted) than P. stratiotes.

See also

Hydrilla (Florida Elodea)
Hydrilla verticillata

Hydrilla, commonly known as Florida Elodea, is also called star vine or oxygen plant. It has also been called Serpicula verticillata, H. alternifolia and H. dentata The exact number of species in the genus is unclear.

Hydrilla has long stems with branch freely. Leaves are 0.4 to 0.8 inches long and 0.08 to 0.2 inches wide and have toothed edges (up to 10-15 teeth) and a toothed midrib on the lower leaf surface. Leaves on the middle and upper stem segments occur in whorls of 2-8 with 4-5 whorls being the most likely configuration. Leaf midveins are often red, however, green midveins are not uncommon. Hydrilla usually feels rough to the touch. Flowers are small, about 0.16 inch across, with 3 white petals, bisexual and appear in sets of 3's.

Hydrilla often floats at the surface where it forms dense mats. It can survive under a variety of conditions including shade, brackish water, and in either still or flowing water. Hydrilla grows so rapidly that it crowds or shades more desirable aquatic plants.

Hydrilla is easily confused with Elodea spp. (which is not restricted) and Egeria densa (which is restricted). Elodea spp (elodea, American elodea, waterweed, or Dutch moss) does not have teeth on the lower leaf midrib and leaves usually appear in whorls of 3. Egeria densa (egeria, Brazilian elodea, anacharis or Elodea densa) has longer leaves (0.6 to 1.2 inches), more teeth on the leaf edge (25-35), and no spines on the lower midvein. Both Elodea spp. and Egeria densa are soft to the touch and have separate flower sexes.

See Also

Lagarosiphon major

Lagarosiphon is also called African elodea. It is somtimes listed as L. muscoides var. major and incorrectly as Elodea crispa.

Lagarosiphon is very similar in appearance to elodea Elodea spp. and hydrilla Hydrilla verticillata. It has long stems (3 feet or longer) that are rooted on the bottom. Leaves are 0.6 to 0.8 inches long and lance-shaped with edges that are slightly serrated or smooth. Leaves often curl downward. Leaf color is usually green with a green midrib. Male and female flowers appear on different plants and are small and have 3 turned-back petals.

Lagarosiphon occurs in still-water lakes and ponds or in flowing streams or rivers. It outcompetes native aquatic plants and poses many of the same problems as hydrilla.

There are many species of Lagarosiphon but only L. major is prohibited in Texas. Because the differences between many of these species is unclear, care should be taken in concluding that a specimen in question is actually L. major.

Eurasian WatermilFoil
Myriophyllum spicatum

Image of Eurasian Watermilfoil courtesty of Plant Conservation Alliance - Alien Plant Working Group.

Eurasian Watermilfoil is also known as European Watermilfoil and fox-tail. It is often confused with Parrot's Feather, Myriophyllum aquaticum, another non-native milfoil introduced through the aquarium plant trade.

Eurasian Watermilfoil has long branching stems up to 6-10 feet in length. Leaves are feather-like, 0.4-1.0 inches long, with 6-16 pairs of leaflets spaced 0.03 to 1.0 inch apart. Leaves grow in whorls of 3 to 6. Steams are often reddish-brown to purple and become reddish-brown to pink when dried; leaves are usually green but become brown when dead or dying. Flower spikes arise from leaf axils and project about the surface of the water. Floweres are pistillate and are 0.06 to 1.0 inch long with a tuft of white or pink on stigma lobes.

Unlike some native milfoils, this species tolerates brackish water to about 12-13 ppt salinity (roughly 1/3 sea water). It requires high light levels for good growth. Eurasian Watermilfoil was introduced through the pet trade. There are many species of watermilfoils sold in the pet trade, but only M. spicatum is prohibited in Texas.

Identification of watermilfoil species can be very difficult; plants growing under poor conditions or which are not flowering may be difficult or impossible to identify. Eurasian Watermilfoil may be confused with other species of watermilfoil found in Texas. The species most likely to be confused with M. spicatum are M. brasiliense (leaf divisions shorter and stouter), M. exalbescens (midstem leaves and leaflets longer), M. verticillatum (midstem leaf worls less than 0.4 inches apart and floral bracts pinnately dissected or lobed), and M. heterophyllum (midstem leaf whorls less than 0.4 inches apart).

See also

Alternanthera philoxeroides

Alligatorweed is also called chaff-flower. It has also been known as Achyranthes philoxeroides and Thelanthera philoxeroides.

Alligatorweed has long, tangled mats which often root from the joints (nodes). Upright stems may be up to 24 inches above the water surface and may be branching to straight. Stems may be hollow if submerged or solid if not submerged. Leavs are oppositely positioned on the stem, and are thick and fleshy, with a smooth edge and oval to lance-shaped (o.8 to 4.3 inches long and 0.2 to 0.8 inches wide). Flowers are small and white and occur in clusters of 6-20 on long stems which arise from leaf axils. Plants are usually yellow-green, but submerged leaves may be reddish-brown.

Alligatorweed grows in still lakes or flowing streams or rivers; it grows in fresh or brackish water with more salinity tolerated in flowing water situations. It may grow rooted to the bottom, in floating mats, or on dry land. Alligatorweed may form dense mats that block access to water and boat traffic.

Several other emergent aquatic plants that may be mistaken for Alligatorweed include Ludwigia spp., Lysimachia spp., Lythrum spp., Dianthera spp. and Polygonum spp.. These plants are smaller in size and have different flower types.

See also

Melaleuca quinquenervia

Paperbark is an Australian tree that may reach over 50 feet in height, rarely 75 feet, but is often found growing as a shrub or smaller tree. The bark is pale brown to whitish and forms in spongy layers. Leaves are alternate and elliptical in shape (2.4 to 4.0 inches long) with 5 parallel veins and short leaf stems. They are aromatic when crushed and are dark green in color. Flowers have 5 white petals, one stigma and 30-40 stamens and may form a "bottle brush" up to 4 inches in length. Seed capsules are woddy and found along the thinner branches.

Paperbark seedlings germinate in shallow water or damp ground and can form dense thickets, blocking access to water and wetland areas. Native vegetation may be rapidly displaced by paperbark thickets. Paperbark has been planted as a windbreak to protect agricultural crops as an an ornamental tree or shrub. It may be frequently be found for sale at garden centers.

See Also

Panicum repens

Torpedograss is a stemmed (up to 28 inches or more) grass arising from nodes or horizontal rhizomes. Leaves of torpedograss are about 0.8 to 0.28 inches wide and may be flattened or folded. Blades are usually green but often have a dull purplish tinge. The flower spike if 2.8 to 4.7 inches tall with branches (spikelets) 0.09 to 0.10 inches long. Flower spikes are often tinted purple.

Torpedograss grows along stream or lake margins in damp soil. Growth is rapid and invasive, and plants may form floating mats extending out into open water. It may also be found in completely terrestial settings. Torpedograss grows rapidly and attains noxious levels quickly. It is extremely difficult to eradicate.

Torpedograss is commonly confused with other panic grasses, particularly Panicum hemitomon.

See also

Water Spinach
Ipomoea aquatica

Water Spinach is also called Aquatic Morning Glory.

Water Spinach is a herbaceous vine, but is not twining or climbing as is typical of most other morning glories. Stems are hollow and trail over muddy banks or float on the water surface. Roots appear at the stem joints. Leaves vary from nearly oval to lance or arrowhead shaped with pointed tips. They occur alternately on the stem. Leaf stocks are long, 2.4 to 6.0 inches, and flowers arise from leaf stem axils. Flowers are composed of 5 petals joined in a funnel shape. They are pink or purplish and often have a purple center. THere are 5 sepals at the flower base, grren in color, and 0.24 to 0.31 inches in length. The roots are not tuberous.

Water Spinach may grow in water or soggy soil in low-land marshes and along stream and river banks. The hollow stems may float in water or extend over muddy banks. It grows rapidly and can quickly cover the surface of an entire body of water. Water Spinach is not cold-tolerant and unlikely to overwinter in North Texas.

Water Spinach should not be confused with other morning glories, none of which are aquatic, but may occur in wetland situations. Ipomoea spp. have variable shaped leaves, however, most are heart, ivy or arrowhead shaped.

See Also

Links To Other Sites


A Field Guide to Aquatic Exotic Plants and Animals
The emphasis here is on exotics found in the Great Lakes region.
Fishing in Texas - Exotic Fish, Shellfish and Plants
The complete list of illegal fish, shellfish and plants for Texas
South Carolina Aquatic Nuisance Species Program - Illegal Plants List
Many of the same plants that are illegal in Texas are also illegal in South Carolina.
USDA: Federal Noxious Weed List
If you can identify a plant, here is where to go to find out if it is officially defined as a "noxious weed".
Aquatic, Wetland and Invasive Plant Particulars and Photographs
Lots of photos and drawings; links to biological controls for most invasives


Nuisance Aquatic Plants in Private Ponds
The focus is on plants detrimental to freshwater fishing in Texas.
Aquatic Weed Control
North Carolina State University has several online publications on pond management and aquatic weed control as well as a fact sheet.
Biological Control of Eurasian Watermilfoil
The milfoil weevil and other control options
Biological Control of Non-Indigenouos Plant Species
Cornell University Department of Natural Resources
Triploid Grass Carp
The focus is on use of Grass Carp in Washington state; most (if not all) states require the same type of permits.
Grass Carp in Texas
Permits and regulations for grass carp


Exotic and Invasive Weeds Research Unit
USDA Agricultural Research Service at UC Davis
US Fish & Wildlife Invasive Species Program
Invasive species definition, legislation and identification
Invasive Plants of Canada Project
Plants native to the southern US can cause problems in Canada.
USGS: Nonindigenous Aquatic Species (NAS)
Covers plants, fish, reptiles, amphibians ... very good listing of links to other websites.
Invasive Species
National Biological Information Infrastructure
South Carolina Aquatic Nuisance Species Program
Plant identification (good pictures) and management
Aquatic Nuisance Species in Vermont
Identifies plants and fish in different categories of impact to state resources
Weeds Gone Wild
The Plant Conservation Alliance's Alien Plant Working Group presents fact sheets and plant lists.
Center for Aquatic and Invasive Plants (University of Florida)
Plant identification, reference database, plant management and an online newsletter.

Information for this article was supplied by

Alien Plant Working Group's Weeds Gone Wild

Texas Parks & Wildlife
4200 Smith School Road
Austin, TX 78744-3291
Phone: 512-389-4800
United States Geological Survey
Biological Resources Division
Florida Carribbean Science Center
Nonindigenous Aquatic Species (NAS)

Home Membership The NTWGS Board
General Information Pond Tour Pond questions? Ask the NTWGS Pond Guy
Water Works Members Resources NTWGS Articles
NTWGS Scrapbook Texas Ponds and Water Gardens Net Ring
Links & things Illegal Aquatics Members Home Pages
Copyright © 1995-2009 by NTWGS, Inc.
Page design and maintenance by Liz Gensheimer and Joe Copeland
Web hosting by Central Iowa (Model) Railroad

Last updated Wednesday, 28-Jan-2009 17:50:06 CST