Since the advent of international trade and travel, humans have either intentionally or inadvertently transported plants to many distant parts of the world. Climate-induced changes in animal migration pathways and ocean currents have also factored into the spread of non-native plants. Rising competition in food production and ornamental plant cultivation has accelerated the naturalization of many invasive plants in warm states like Texas.
Non-native plants become noxious weeds when they are able to significantly compete with native plant populations and cause shifts to the local ecology. Often considered ecosystem engineers, these tend to be aggressive growers – able to create colonies and disperse by multiple means. They either spread as clonal escapees from their original locations or they may be carried into other environments by human, animal, and other physical vectors.
Invasive plants are found in practically all types of biomes in Texas. Though these may be valuable to landowners in a controlled setup, their cultivation is typically discouraged due to the negative impacts of their spread. Landowners in the state are now expected to responsibly control introduced plants as they are associated with environmental, economic, and health-related threats.
1) Common Bermuda grass (Cynodon dactylon)
Common Bermuda grass is, by far, one of the most ecologically destructive non-native crops in Texas. Introduced into the southern US as a lawn and field grass in the 1800s, this species is remarkably difficult to control and remove due to its deeply-rooted rhizomes and rapid rate of spread. Highly fertile and tolerant of various habitats, this turfgrass is also able to reproduce by seed. In agricultural landscapes, it can be especially bothersome as it readily competes with the more valuable types of local grasses.
2) Indian goosegrass (Eleusine indica)
Indian goosegrass is a prolific annual that favors warm conditions. It is a troublesome weed in many Texan fields, golf courses, and other high-traffic zones. Especially competitive in areas where native turfgrass cover is sparse, it is prolific enough to form infestations. These are extremely challenging to manage because they form extensive root systems and are able to self-seed. Their roots are able to permeate through tough substrates, and herbicides are usually necessary to impede their growth.
3) Persian silk tree (Albizia julibrissin)
Though the Persian silk tree has the potential to be a lovely ornamental plant, its cultivation is discouraged in Texas. Prone to becoming invasive and contracting diseases, it can spread via vegetative and sexual means. Its seeds, which remain viable for dozens of years, are produced in large quantities each year. Easily dispersed by animals and by stormwaters, the seeds can germinate in disturbed areas. They grow into small trees with a tolerance for droughts, salt, and wind.
4) Privets (Ligustrum spp.)
Privets are small trees or shrubs with an evergreen or deciduous nature. Initially spread throughout the US as attractive border or hedge plants, these species have a knack for outcompeting native vegetation. Fast-growing, escaped stands can eventually dominate large areas in woodland and riparian forests. In Texas, both large leaf privets (L. lucidum, L. japonicum, and L. vulgare), and small leaf privets (L. sinense and L. quihoui) are able to alter conditions by producing dense thickets in the understory.
5) Chinese tallow tree (Triadica sebifera)
Also called the candleberry tree and Florida aspen, the Chinese tallow tree thrives in prairie regions, disturbed farmlands, damaged woodlands, and along roadsides. It tends to form noxious monoculture stands in the southern and eastern regions of Texas. These stands cover hundreds of acres and are able to expand quickly due to their vigorous reproductive ability. Their success as non-native competitors has damaged local ecosystems and reduced species diversity.
6) Japanese honeysuckle (Lonicera japonica)
Often grown as an ornamental plant due to its flexible, versatile stems and attractive blooms, the Japanese honeysuckle is much more harmful than it may initially appear. Though it continues to be intentionally cultivated in many parts of the US, it should be grown with caution as its escaped seeds and shoot fragments readily invade floodplains, disturbed areas, and roadsides. Though its fragrant white, purple, or yellow blooms can serve as a nutritious food source for many herbivores and pollinators, they are borne on shoots that can disform and inhibit the growth of native shrubs and trees.
7) Water hyacinth (Pontederia crassipes)
Water hyacinth inflorescences can bring a seemingly spellbound beauty to water features, but they don’t make up for the fact that they are borne on aggressive runners. One of the most rapidly-spreading hydrophytes, this species can multiply at exponential rates to eventually fill out and suffocate entire ponds. Known for thriving in nutrient-rich water bodies, a single specimen of this plant can double in size in a matter of just 2 weeks! Though it may be tempting to cultivate a small stand in your own pond, try to opt for native alternatives instead.
8) Elephant ear (Colocasia esculenta)
An alluring addition to tropical gardens, the elephant ear or “taro” is set apart by its large, heart-shaped leaves. Borne on lengthy and relatively large petioles, the leaves can measure as much as 16 inches (41 cm) long and 10 inches (25 cm) wide. In Texas, this water-loving herb is found in bayous and lake shorelines, where it tends to outcompete native plants. Though it is a recipient of the RHS Award of Garden Merit, its dense stands can be tricky to manage and cut back.
9) Common giant mustard (Rapistrum rugosum)
The common giant mustard, also known as “bastard cabbage”, tends to form monoculture stands in many parts of the US. This successional plant thrives in disturbed areas, including roadsides and damaged agricultural landscapes. It has begun to threaten natural forests and wetland zones in Texas as its dense rosettes of basal leaves can prevent native seeds from germinating. Its own seeds are often carried into other locations via contaminated mulch and grass. Resistant to some herbicides, its spread may be difficult to control.
10) Giant reed (Arundo donax)
True to its name, the giant reed can grow to towering heights of 33 feet (10 meters) in optimal environments. This tall cane grass can rapidly spread through vegetative means. Its fibrous rhizomes form tough mats that may penetrate deeper layers of nutrient-rich soils. They can tolerate floods and may even be transported into other locations via stormwater flow. In Texas, the giant reed can alter wetlands by creating natural dams. Its tough stands can even damage built structures.
11) Brazilian vervain (Verbena brasiliensis)
Initially exported outside of its native range as an ornamental plant, Brazilian vervain is a flowering annual herb. It produces terminal inflorescences with bluish-purple flowers. Hardy to USDA zones 7 – 10, this drought-tolerant plant chiefly spreads via its seeds. It is considered a significant invasive weed in Texas as it can displace native plants and quickly adapt to suboptimal conditions. It is a minor food source for small mammals and birds, so these animals may serve as vectors for its spread.
12) Golden bamboo (Phyllostachys aurea)
A type of “running bamboo”, the golden bamboo is named for its yellow canes. These become more golden-brown as the plant ages and is exposed to full sun conditions. Often grown as a natural hedge or screen, this species has the tendency to become a pest plant. In warm and consistently moist soils, its escapees can form monospecific stands that are exceedingly difficult to control. In Texas, it can alter the structural diversity of wild habitats and prevent native plants from accessing sunlight and water.
13) Hydrilla (Hydrilla verticillata)
Now found all across the globe as a rapidly spreading hydrophyte, hydrilla is one of the most popular ornamental plants for indoor aquariums and outdoor water features. This vigorous spreader can tolerate both cool and warm waters, including those with slightly saline conditions. One of its main modes of competition is its production of allelopathic compounds. These may inhibit the growth of other nearby hydrophytes, giving them more room to access sunlight and nutrients in the water column.
In Texas, hydrilla infestations are problematic because they can compromise water flow into agricultural areas. As they may cause water to become stagnant, they also unfortunately promote the spread of mosquitoes.
14) Eurasian watermilfoil (Myriophyllum spicatum)
Infamous for being one of the most destructive invasive plants in North America’s wetlands, the Eurasian watermilfoil is a submerged hydrophyte. It thrives best in slow-moving and still freshwater systems, where its root system can quickly become well-established and its upright shoots can trail toward the water’s surface.
Though its whorls of feathery leaflets provide food and cover for many small aquatic animals, they can significantly impede the flow of water, block out light, and prevent apex predators from effectively finding prey. As it threatens the survival of many native species, sightings of this plant must be reported to the Texas Parks and Wildlife Department.
15) Johnsongrass (Sorghum halepense)
A member of the Poaceae family of true grasses, johnsongrass has been introduced to all continents save Antarctica. This hardy grass is likely to become invasive if its growth is left unchecked. As it rapidly spreads via its seeds and its networks of tough rhizomes, it can compete with valuable crops. It is not especially desirable as a forage crop because its foliage tends to be rich in nitrates and cyanide. Its monocultures are often found in roadside areas, irrigation ditches, and disturbed landscapes.
16) Giant salvinia (Salvinia molesta)
Giant salvinia is a free-floating aquatic fern with leaves that effortlessly float on the surface of calm waters. Each pair of its bristly leaves is connected to a suspended frond, which extends downward toward the water column and functions much like a root. Accidentally introduced into multiple bodies of water across the US, it has become an invasive species with the potential to damage entire freshwater ecosystems. Its noxious fronds form thick weed mats that can block sunlight and inhibit recreational activity in waterways.
17) Salt cedar (Tamarix ramosissima)
A small tree with many ornamental qualities, the salt cedar is named for its tolerance for salt water. Capable of excreting excess salts via specialized glands (creating salt deposits), it has the capacity to be highly competitive in frequently flooded areas. Although it is a noxious weed in many riparian habitats in the southern to southwestern US, it continues to be grown as a natural screen, windbreak, and specimen tree. Seedlings that escape into forests and eventually dominate the understory can displace native species, endangering their survival.
18) Yellow nutsedge (Cyperus esculentus)
Also called the “tiger nut” or “earth almond”, the yellow nutsedge is intentionally cultivated throughout its native range as a source of edible tubers. Solitary, upright stems and horizontally spreading rhizomes arise from these tubers. Able to thrive in disturbed soils, they can form extensive, monoculture stands that disrupt a habitat’s ecological balance and displace many native animals and plants. For these reasons, this species is regarded as one of the world’s worst weeds.
19) Tree of heaven (Ailanthus altissima)
A temperate, deciduous tree, the tree of heaven can grow to a full height of about 50 feet (15 meters). Known for vegetatively spreading via suckering roots, it can quickly form clonal colonies in landscapes with moist and loamy soils. Due to its hardy and highly adaptable nature, however, its stands can be found wherever there is ample sunlight and space. In some parts of the US, it has produced dense thickets that have stifled the growth and survival of many native trees and shrubs.
20) White mulberry (Morus alba)
Having been cultivated for thousands of years as a host plant for nourishing silkworms, the white mulberry is now found far beyond its native range. This rapidly growing yet short-lived tree can survive in temperate to tropical regions with a wide range of soil types. Though it favors well-draining substrates, its stands can also adapt to poor soils. For this reason, it tends to dot roadsides and disturbed urban areas in Texas. It can hybridize with and displace its close cousin, the red mulberry (M. rubra).
21) Giant Asian dodder (Cuscuta japonica)
The giant Asian or Japanese dodder is also called “strangleweed” because its stems wrap around living host plants and hijack their nutrients. Technically a parasitic vine, it can significantly weaken its host and eventually cause it to die back. The stems of this vine are yellowish-green and about as thick as a pencil. These grow remarkably fast and can spread to new habitats via fragmentation or seed production. Infestations need to be treated as soon as they are spotted to prevent the stems from attacking more plants.
22) Chinaberry tree (Melia azedarach)
A member of the Meliaceae or mahogany family, the Chinaberry tree is widely cultivated as an ornamental plant and as a source of timber and fodder. Though it is considered an invasive species in many parts of the US, it continues to be grown and sold by many plant nurseries due to local demand. Attractive to hummingbirds, it produces spritely inflorescences with small purple blooms. Once these are pollinated, they develop into toxic, light yellow berries. The rest of this plant’s parts are toxic as well.
23) Holly fern (Cyrtomium falcatum)
Perfect for low-light and consistently moist zones of the garden, holly fern is often cultivated as a shade ornamental. Unfortunately, its escaped stands have begun to wreak havoc in some parts of Texas, where they can be found growing through gaps in brick walls, rocky habitats, and limestone cliffs. Hardy to USDA zones 6 – 10, this species can compete with other native ferns and rare bryophytes for space and nutrients. Some of its stands have become naturalized in the wild.
24) Maltese star thistle (Centaurea melitensis)
The Maltese star thistle is an annual, flowering herb that grows to about 4 feet (1.2 meters) tall in optimal conditions. It is distinguished by its rosettes of basal leaves, which are linear and narrow yet deeply lobed. These emerge from shallow taproot systems with no rhizomes or suckers. Despite the lack of self-propagating root structures, however, this species has spread far and wide because of its vast quantities of seeds. These can germinate and eventually grow into thriving seedlings in disturbed grasslands, roadsides, and agricultural landscapes.
25) Chinese wisteria (Wisteria sinensis)
Remarkably eye-catching as an ornamental vine, the Chinese wisteria has been introduced into many temperate regions because of its fragrant, spring inflorescences. Downward-facing, these are set apart by their simultaneous blooms of blue, violet, or white flowers. The downside to growing this beautiful plant is it does spread via suckering roots. If left to grow freely, it can quickly outgrow and displace native vegetation. An abundance of its trailing stems can cast host plants in shade, cut through their tissues, and deprive them of nutrients.
26) Kudzu (Pueraria montana var. lobata)
Dubbed the “invasive vine that ate the South”, kudzu is another extremely problematic plant. Also known as Japanese arrowroot, it has trailing stems that elongate at a remarkably fast pace. In optimal conditions, they can boast a length increase of about one foot per day! Over time, the stems can grow over both natural and manmade structures, completely coating them in leaves and blocking out all traces of sunlight. Its escaped stands usually need to be treated with chemical herbicides to prevent them from damaging entire ecosystems.
27) Catclaw vine (Dolichandra unguis-cati)
A member of the Bignoniaceae family of trumpet vines, the catclaw vine can cause widespread and irreversible damage to forest ecosystems. Capable of growing in virtually all layers of woodland habitats, this woody vine uses trees and shrubs to gain vertical elevation and access more space and sunlight. It develops extensive and aggressive root systems in a wide range of soils, especially those which are frequently moistened by rainwaters. Moreover, nodes along its stems are able to generate roots whenever they come into contact with appropriate substrates.
28) Chaste tree (Vitex agnus-castus)
Among species classified under the Vitex genus, the chaste tree is one of the few that thrives best in temperate regions. Though it has a wealth of ornamental features, it is not particularly desirable as a landscape tree in Texas. This is due to its tendency to spread and become invasive in the state’s southern regions, which experience fairly warm winters. Tolerant of prolonged droughts, the chaste tree can compete with other native trees and form problematic stands in limestone outcrops.
29) Taiwanese photinia (Photinia serratifolia)
Throughout its native range, the Taiwanese photinia occurs as an evergreen tree. It is set apart by its dense spring bouquets of showy, heavily-scented blooms and its red fall leaves. Often grown as an urban tree, it tends to thrive along the borders of busy avenues in heavily populated cities. In Texas, this species is occasionally cultivated as an ornamental plant. Unfortunately, its seeds are often carried into forests and creek beds, where they can quickly germinate and crowd out native flora.
30) Deep-rooted sedge (Cyperus entrerianus)
The deep-rooted sedge was accidentally brought into Texas in the mid-1900s. Since then, it has gradually spread throughout disturbed prairies, flatwoods, ditches, and rice fields. Prone to forming monospecific stands, it can outcompete native grasses, sedges, and many other less aggressive herbs. In agricultural landscapes, its infestations can cause significant damage to crops. Local measures of control include mowing sedge stands (though this may also spread its seeds) and using chemical herbicides.
