Illegal and Invasive PlantsTexas Law
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.
Download Revised Exotic Species Rules now!
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 .
|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|
|Rooted Water Hyacinth||Pontederiaceae||Eichhornia azurea|
|Water Spinach||Convovulaceae||Ipomoea aquatica|
|Giant Salvinia||Salviniaceae||Molesta spp.|
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.
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.
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.
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.
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.
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 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).
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.
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.
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.
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.
Information for this article was supplied by
Texas Parks & Wildlife
4200 Smith School Road
Austin, TX 78744-3291
United States Geological Survey
Biological Resources Division
Florida Carribbean Science Center
Nonindigenous Aquatic Species (NAS)
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