Photos of Invasive Plants

Invasive plant species are plants that are non-native to a region and cause harm to the environment, economy, or human health. These plants spread aggressively and displace native species, often causing drastic changes to ecosystems. Learning to identify invasive plants is an important skill for land managers, conservationists, and nature enthusiasts. Photographs are useful tools for identifying and documenting the spread of invasive plants. This article provides an extensive collection of photos of major invasive plant species to assist with identification and management efforts.

Common Invasive Plant Species in the United States

The United States has been invaded by thousands of non-native plant species. Some of the most widespread and disruptive invasive plants include:

Kudzu

Kudzu (Pueraria montana) is a fast-growing perennial vine that completely engulfs native vegetation. It forms massive blanket-like infestations and contributes to soil erosion.

Kudzu growing on trees. Photo credit: James H. Miller, USDA Forest Service, Bugwood.org

Japanese Knotweed

Japanese knotweed (Fallopia japonica) is an upright perennial shrub that forms dense thickets. It spreads quickly along roadsides and waterways, altering natural ecosystems.

Japanese knotweed bamboo-like stems. Photo credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Purple Loosestrife

Purple loosestrife (Lythrum salicaria) is a wetland invader with prolific seed production. It crowds out native grasses and wildflowers, degrading wildlife habitat.

Purple loosestrife flowering in a wetland. Photo credit: Dave Jackson, Sault College, Bugwood.org

Phragmites

Common reed (Phragmites australis) is a tall perennial grass that forms dense stands in wetlands, decreasing biodiversity. It alters hydrology and increases fire potential.

Phragmites towering over a marsh. Photo credit: Connecticut Department of Energy and Environmental Protection, Bugwood.org

Tree of Heaven

Tree of heaven (Ailanthus altissima) is an aggressive tree species that grows in disturbed areas. It produces toxins that inhibit the growth of other plants.

Tree of heaven with smooth gray bark. Photo credit: Chris Evans, Illinois Wildlife Action Plan, Bugwood.org

Multiflora Rose

Multiflora rose (Rosa multiflora) is a prolific shrub that forms impenetrable thickets, outcompeting native shrubs and reducing wildlife habitat.

Multiflora rose thicket. Photo credit: Chuck Bargeron, University of Georgia, Bugwood.org

Mile-a-Minute Weed

Mile-a-minute weed (Persicaria perfoliata) is an herbaceous annual vine with distinctive barbed stems. It climbs over other plants, blocking access to light.

Mile-a-minute weed covering other plants. Photo credit: Gerald Holmes, Valent USA Corporation, Bugwood.org

Cheatgrass

Cheatgrass (Bromus tectorum) is a winter annual grass that forms dense carpets in the western U.S. It increases fire frequency and intensity.

Cheatgrass covering a landscape. Photo credit: Steve Dewey, Utah State University, Bugwood.org

Emerald Ash Borer

Emerald ash borer (Agrilus planipennis) is a beetle that bores into ash trees, disrupting nutrient and water transport. It has killed millions of ash trees.

Emerald ash borer adult beetle. Photo credit: David Cappaert, Michigan State University, Bugwood.org

Impacts of Invasive Plants

Invasive plants can have severe ecological and economic consequences:

• Displace native vegetation
• Decrease biodiversity
• Alter ecosystem functions like nutrient cycling and hydrology
• Interfere with agriculture and forestry
• Clog waterways and increase flooding
• Increase soil erosion and sedimentation
• Reduce wildlife habitat and forage
• Increase wildfire risk
• Damage infrastructure
• Reduce recreational opportunities

Managing invasive plants is crucial but challenging. Prevention of introduction and early detection are the most effective and economical management approaches. Public education regarding invasive plant identification is vital. Once established, invasive plants are difficult to eradicate fully. Control efforts like herbicide application, burning, mowing, or biocontrol insects can help reduce invasive plant dominance and allow native plants to recover.

Invasive Plants by Region

Invasive plant species present significant threats across all regions of the United States:

West

Major invasive plants of western North America:

• Cheatgrass: Alters fire regimes and reduces native plant diversity
• Tamarisk: Displaces native vegetation and increases soil salinity
• Russian olive: Forms dense thickets along riparian areas
• Leafy spurge: Toxic to cattle and displaces native grasses
• Medusahead: Unpalatable grass that reduces rangeland quality
• Yellow starthistle: Noxious invader on grasslands that can harm livestock

Leafy spurge infestation. Photo credit: Norman E. Rees, USDA Agricultural Research Service, Bugwood.org

Midwest

Problematic invasive plants of the Midwest include:

• Reed canarygrass: Aggressive wetland invader that forms dense stands
• Garlic mustard: Displaces native woodland wildflowers
• Common and glossy buckthorn: Form dense thickets and reduce tree recruitment
• Wild parsnip: Noxious weed that can cause severe skin burns
• Autumn olive: Alters soil nitrogen cycling and crowds out native shrubs
• Musk thistle: Spreads rapidly on prairies and reduces forage

Dense stand of reed canarygrass. Photo credit: Chuck Bargeron, University of Georgia, Bugwood.org

Northeast

Major invasive plant threats in the northeastern U.S. include:

• Japanese barberry: Spreads rapidly and provides habitat for deer ticks
• Oriental bittersweet: Smothers native vegetation
• Japanese stiltgrass: Prolific annual that carpets forest floors
• Burning bush: Ornamental shrub that escapes into forests and forms dense thickets
• Mugwort: Allergenic invader of fields, roadsides, and thickets
• Water chestnut: Forms dense floating mats that impact recreation and ecosystems

Burning bush shrub. Photo credit: Ohio State Weed Lab, The Ohio State University, Bugwood.org

Southeast

Major invasive plant issues in the southeastern U.S. include:

• Cogongrass: Highly flammable invader that alters fire regimes
• Chinese tallow: Aggressive wetland tree that displaces native cypress-tupelo forests
• Japanese climbing fern: Smothers native vegetation in forests and reduces tree recruitment
• Chinese privet:Forms dense thickets and lowers plant diversity
• Tropical soda apple: Toxic to livestock and displaces forage
• Air potato: Vigorous vine that climbs and smothers native vegetation

Tropical soda apple infestation. Photo credit: Forest & Kim Starr, Starr Environmental, Bugwood.org

Impacts on Natural Areas and Wildlife

Invasive plants profoundly alter native habitats and threaten biodiversity:

• Infestations in western rangelands degrade habitat for greater sage-grouse and other wildlife. Cheatgrass fuel beds increase wildfire frequency, further impacting sagebrush ecosystems.

Cheatgrass degrading sagebrush habitat. Photo credit: USDA Forest Service

• Dense reed canarygrass stands degrade wetland and riparian habitat, reducing nesting sites for marsh birds like bitterns and rails.

American bittern camouflaged in native reeds. Photo credit: USFWS

• In the Northeast, mile-a-minute weed degrades important forest habitat for declining pollinators like the rusty-patched bumble bee.

Rusty patched bumble bee relying on native wildflowers. Photo credit: FWS

• Tamarisk infestations along southwestern rivers negatively impact habitat for endangered fish like the Colorado pikeminnow.

Colorado pikeminnow. Photo credit: USFWS

• In Florida, climbing ferns smother native vegetation, reducing habitat for threatened species like the frosted flatwoods salamander.

Frosted flatwoods salamander. Photo credit: USFWS

Spread of Invasive Plants

There are many vectors that contribute to invasive plant introductions and spread:

• Intentional ornamental introductions: Plants like purple loosestrife were brought for gardens but later escaped
• Contaminated agricultural seed mixes: Weedy species spread via crop and pasture seeds
• Right-of-way disturbances: Road, trail, and utility work creates habitat for invaders
• Vehicles and equipment: Seeds cling to tires, undercarriages, and machinery
• Animal dispersal: Seeds spread via fur, droppings, or adhesion
• Natural mechanisms: Wind, water, and wildlife spread seeds of plants like cheatgrass
• Soil disturbance: Invasive seed banks emerge following events like fire or grading
• Dumping of yard waste: Invasive escapes like Japanese knotweed spread from dumped clippings
• Nursery stock: Shipping material transports stowaway pests like emerald ash borer

Quarantines, nursery sanitation, and cleaning of vehicles/gear in high-risk areas can help slow the human-assisted spread of invasives. Restoring disturbed sites quickly using native plants can also make areas less vulnerable to invasion. Public education is key to build awareness on this issue.

Gear inspection after recreating in areas with invasive plants. Photo credit: US Forest Service

Management and Control

Controlling established invasive plants is extremely challenging. Prevention and early detection of new infestations are the best strategies. Public education and land manager training on invasive plant identification are critical for quick reporting of new outbreaks.

For established infestations, integrated vegetation management strategies are required. Techniques include:

• Manual removal: Hand pulling, digging, or cutting for small populations
• Mowing/weed-whacking: Can reduce vigor and seed production
• Grazing: Targeted livestock grazing at key phenological stages
• Prescribed burning: Can help control fire-intolerant invasives
• Flooding: Water management useful against terrestrial weeds
• Solarization: Covering soils with plastic to increase heat and kill plants/seeds
• Herbicide applications: Foliar sprays or cut stump treatments
• Biocontrol: Permitted introduction of host-specific natural enemy insects

Volunteers hand pulling garlic mustard. Photo credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Follow-up monitoring and additional treatments are almost always needed. Restoration with competitive, native vegetation can help resist reinvasion. Preventing new introductions and infestations through regulation, education, and vigilance is imperative. Everyone must do their part to detect and report invasive plants early before they get established and become ecological disasters.

Frequently Asked Questions

What are some key tips for identifying invasive plants?

Some key tips for identifying invasive plants include:

• Learn to recognize their distinguishing features like flowers, seed heads, leaf patterns, stem textures, odors, etc. Reference field guides and online image databases.
• Compare suspected invasive plants to known native lookalikes. Learn the subtle differences.
• Document exactly where suspected invasive populations are located and their extent. Note density and impacts.
• Consider the context. Does it appear in natural settings where it should not belong? Is it spreading aggressively?
• When in doubt, collect photos and samples. Ask experts for assistance identifying species.

What makes invasive plants so successful at establishing and spreading?

Invasive plants possess a variety of traits that give them advantages over native plant species, allowing them to establish, spread aggressively, and become dominant. These traits include:

• Rapid growth: Invasives like kudzu grow extremely fast, quickly shading out native plants.
• Prolific reproduction: Some invasives produce enormous amounts of seeds that build up soil seed banks.
• Persistent seeds: Seeds of invaders like purple loosestrife remain viable in soils for many years.
• Early germination: Some invasives get a head start on natives by sprouting earlier in spring.
• Extended growing season: Warm-season invaders like Japanese stiltgrass continue growing late into fall.
• Adaptability: Invasives tolerate a wide range of environmental conditions.
• Few natural enemies: Plants escape control by specialist herbivores of their native range.
• Allelopathy: Some invaders release natural herbicidal compounds that harm neighboring plants.
• Tolerance to disturbance: Invasives capitalize on disturbances like tilling that hurt native plants.
• Prolific asexual spread: Plants like black swallow-wort spread rapidly via rhizomes and roots.

How do invasive plants harm native ecosystems?

Invasive plants can profoundly disrupt native ecosystems in diverse ways:

• Displacing native plants: Invasives outcompete native plants for resources like light, water, and nutrients. Diverse native plant communities are replaced by invasive monocultures.
• Altering soils: Some invaders change soil chemistry, nutrients, or microbes in ways that give them a continued advantage over natives.
• Modifying hydrology: Dense invasive stands like phragmites impede water flow in wetlands. Some invaders draw down water tables.
• Increasing fire risk: Invasive grasses promote bigger, more frequent fires that are destructive to native communities not adapted to frequent burning.
• Promoting erosion: Invasive plants displace deep-rooted native plants that stabilize soils, increasing erosion potential.
• Reducing wildlife food and habitat: Native insects and herbivores are not adapted to utilize invasive plants. Dense stands degrade habitat complexity.
• Altering ecosystem functions: Fundamental processes like nutrient cycling, soil development, and pollination relationships are disrupted.
• Homogenizing nature: Diverse native communities are replaced by a few dominant invasive species, decreasing biodiversity at genetic, species, and landscape levels.

What can individual citizens do to combat invasive plants?

There are many ways citizens can help fight invasive