NON-NATIVE INVASIVE SPECIES

Hundreds of species of non-native plants, animals, and fungi have been intentionally or unintentionally introduced into Delaware since the first arrival of European settlers in the 1600’s. These plants and animals were introduced for agricultural, horticultural, wildlife management and other reasons.  Others were accidentally introduced. Some of these non-native species have responded to Delaware’s environment with great vigor, spreading aggressively into many natural habitats out competing native species.  In addition, these foreign species had very few predators to keep their populations in check. 

These invasions continue to occur and many of our worst non-native species have been introduced in the past 75 years.  Plants like Callery (e.g., Bradford) pear, multiflora rose, autumn olive, bush honeysuckle, Japanese honeysuckle, oriental bittersweet, porcelainberry, mile-a-minute, English ivy, phragmites, and many other plants , can and do interrupt natural plant succession by smothering native plants.  Animals – such as snakeheads, blue catfish, flat-headed catfish, several species of mollusks, and insects like the gypsy moth and emerald ash borer – can have serious, even lethal effects on native species and their habitats.    

To reduce these negative effects on natural plant and animal communities we must develop and implement major efforts of control. While eradication would be ideal, in practice it is very difficult to eliminate most specie, therefore the primary goal of most control projects is to reduce non-native populations to levels that have minimum impact on natural habitats and their processes.

Efforts to combat the spread of non-native species are underway in Delaware.  Although funding is limited, state, county, and municipal governments, non- governmental organizations and private citizens continue to find new and more effective ways to control non-native intruders.

One recent control measure is the ban of the sale of many of the most disruptive of Delaware’s non-native invasive plants.  This law, which went into effect in July of 2022, prohibits the sale of 37 species of non-native plants (see list).  There is much more that can and should be done to control non-native invasive plants and animals in the First State.

Common Name: Amur honeysuckle

Scientific Name: Lonicera maackii

Origin: East Asia

Description: Amur honeysuckle is a deciduous shrub that can grow up to 15–20 feet tall. It has opposite, ovate leaves and produces fragrant, tubular white flowers that turn yellow with age. The plant thrives in a variety of habitats, including forests, fields, and disturbed areas, often forming dense thickets that outcompete native vegetation. It propagates through abundant red berries, which are dispersed by birds, facilitating its spread across suitable habitats.

Attribution: Lonicera_maackii_2.jpg (2683×4027)

Common Name: Autumn olive

Scientific Name: Elaeagnus umbellata

Origin: East Asia

Description: Autumn olive is a deciduous shrub or small tree reaching heights of 12–20 feet. It features silvery scales on the underside of its leaves and produces small, fragrant, cream-colored flowers. The plant is adaptable to various soil types and is commonly found in open fields, forest edges, and roadsides. Its red, fleshy fruits are readily eaten by birds, which disperse the seeds, leading to rapid colonization of new areas.

Attribution: https://commons.wikimedia.org/wiki/File:Elaeagnus_umbellata_fruit.jpg

Common Name: Callery pear

Scientific Name: Pyrus calleryana

Origin: East Asia

Description: The Callery pear is a deciduous tree that can grow up to 30–50 feet tall, with a pyramidal to rounded crown. It has glossy, ovate leaves and produces abundant white flowers in early spring. The tree is often found in urban settings, disturbed areas, and along highways. Its small, round fruits are consumed by birds, aiding in seed dispersal and the establishment of new populations in various habitats.

Attribution: Le.Loup.Gris, CC BY-SA 3.0

Common Name: Chinese wisteria

Scientific Name: Wisteria sinensis

Origin: China

Description: Chinese wisteria is a deciduous woody vine known for its vigorous growth, capable of reaching lengths of up to 40 feet or more. It has pinnately compound leaves and produces cascading clusters of fragrant, purple to bluish flowers in spring. Preferring moist woodlands, stream edges, and disturbed areas, it climbs over trees and structures, often leading to structural damage and shading out native vegetation. It propagates through seed pods and can also spread vegetatively via rooting at nodes.

Attribution: Michal Klajban, CC BY-SA 4.0

Common Name: Creeping water primrose

Scientific Name: Ludwigia peploides subsp. glabrescens

Origin: North and South America

Description: Creeping water primrose is a perennial herb that grows in moist to wet areas, including the edges of ponds, streams, and wetlands. The stem can creep over 2 meters long, sometimes branching, and spreads to form mats on the mud or floats ascending in the water. The leaves are several centimeters long and are borne in alternately arranged clusters along the stem. It produces 5 to 6 bright yellow petals up to 2.4 centimeters long. The fruit is a hard, cylindrical capsule. It propagates through stem fragments or rhizomes broken off by wind, water flow, or animals, allowing it to spread across suitable habitats.

Attribution: Eugene Zelenko, CC BY-SA 4.0 httpscreativecommons.orglicensesby-sa4.0, via Wikimedia Commons

Common Name: English ivy

Scientific Name: Hedera helix

Origin: Europe, Western Asia, North Africa

Description: English ivy is an evergreen climbing vine that can reach heights of 20–80 feet when attached to vertical surfaces. It has leathery, dark green, lobed leaves and produces small, greenish flowers in late summer to early fall, followed by black berries. It thrives in a variety of habitats, including forests, urban areas, and disturbed sites, often forming dense ground cover or climbing and smothering trees and buildings. It spreads both vegetatively, through rooting at stem nodes, and by seeds dispersed by birds that consume the berries.

Attribution: Nathan Nyx, CC BY-SA 4.0

Common Name: European privet

Scientific Name: Ligustrum vulgare

Origin: Europe, North Africa, Western Asia

Description: European privet is a deciduous shrub that typically grows 4–15 feet tall, with opposite, lanceolate leaves and clusters of small, white, fragrant flowers in late spring to early summer. It is commonly found in hedgerows, forest edges, and disturbed areas. The plant produces small, black berries that are readily eaten by birds, facilitating seed dispersal and the establishment of new populations.

Attribution: Andrew Lih, CC0, via Wikimedia Commons

Common Name: European reed

Scientific Name: Phragmites australis subsp. australis

Origin: Europe, Asia, Africa

Description: European reed is a tall, perennial grass that can reach heights of up to 15 feet. It has broad, lanceolate leaves and produces large, feathery flower plumes in late summer. Commonly found in wetlands, marshes, and along waterways, it forms dense stands that displace native vegetation and alter hydrology. It propagates through both wind-dispersed seeds and extensive rhizome networks, allowing it to rapidly colonize and dominate new areas.

Attribution: Le.Loup.Gris, CC BY-SA 3.0

Common Name: Garlic mustard

Scientific Name: Alliaria petiolata

Origin: Europe

Description: Garlic mustard is a biennial herb that grows up to 3 feet tall, with heart-shaped, coarsely toothed leaves that emit a garlic odor when crushed. In its second year, it produces clusters of small, white, four-petaled flowers. Commonly found in forest understories, along trails, and in disturbed areas, it thrives in shaded environments. The plant reproduces solely by seed, producing large quantities that can remain viable in the soil for several years, facilitating its rapid spread and displacement of native flora.

Attribution: Robert Flogaus-Faust, CC BY 4.0

Common Name: Hydrilla

Scientific Name: Hydrilla verticillata

Origin: Asia, Africa, Australia

Description: Hydrilla is a submerged aquatic perennial that can grow up to 30 feet in length, forming dense mats beneath the water surface. It has slender stems with whorls of small, pointed leaves that are serrated along the margins. Typically found in freshwater bodies such as lakes, rivers, and ponds, it thrives in a variety of nutrient conditions. The plant propagates through fragmentation, tubers, turions, and seeds, with fragments easily taking root and forming new plants, leading to rapid colonization and interference with native aquatic ecosystems.

Attribution: Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0

Common Name: Japanese barberry

Scientific Name: Berberis thunbergii

Origin: Japan

Description: Japanese barberry is a deciduous shrub that grows 2 to 8 feet tall, with arching branches bearing small, oval, green to bluish-green leaves. It produces small, yellow flowers in spring, followed by bright red berries in fall. Commonly found in forests, open woodlands, and disturbed areas, it tolerates a range of soil types and light conditions. The plant reproduces by seed, with birds dispersing the berries, and can also spread vegetatively through its root system, forming dense thickets that outcompete native vegetation.

Attribution: Lazaregagnidze, CC BY-SA 3.0

Common Name: Japanese honeysuckle

Scientific Name: Lonicera japonica

Origin: East Asia

Description: Japanese honeysuckle is a perennial, woody vine that can climb up to 30 feet or sprawl along the ground. It has opposite, oval leaves and produces fragrant, tubular white flowers that turn yellow with age. The plant thrives in a variety of habitats, including forests, fields, and disturbed areas, often forming dense mats that smother native vegetation. It propagates through seeds, which are dispersed by birds, and by rooting at stem nodes, facilitating its spread across suitable habitats.

Attribution: Sesamehoneytart, Lonicera japonica Japanese honeysuckle, CC BY-SA 3.0

Common Name: Japanese pachysandra

Scientific Name: Pachysandra terminalis

Origin: Japan, China

Description: Japanese pachysandra is an evergreen, herbaceous perennial that grows up to 12 inches tall, forming dense mats of glossy, oval leaves. It produces small, white flowers in early spring. Commonly used as a groundcover in shaded gardens, it can escape cultivation and invade forest understories, where it outcompetes native plants. The plant spreads primarily through creeping stolons, allowing it to form extensive colonies. Seed production is rare and not a significant factor in its propagation.

Attribution: Agnieszka Kwiecień, Nova, CC BY-SA 4.0

Common Name: Japanese stiltgrass

Scientific Name: Microstegium vimineum

Origin: East Asia

Description: Japanese stiltgrass is an annual grass that grows 1 to 3.5 feet tall, with pale green, lance-shaped leaves featuring a distinctive silvery stripe along the midrib. It produces delicate, spike-like flower clusters in late summer. Typically found in forest understories, along trails, and in disturbed areas, it thrives in shaded, moist environments. The plant reproduces solely by seed, producing large quantities that can remain viable in the soil for several years, facilitating its rapid spread and displacement of native flora.

Attribution: James H. Miller & Ted Bodner, Southern Weed Science Society, Bugwood.org, CC BY 3.0

Common Name: Lesser celandine

Scientific Name: Ficaria verna

Origin: Europe, West Asia, North Africa

Description: Lesser celandine is a low-growing, herbaceous perennial that forms dense mats of dark green, heart-shaped leaves. It produces bright yellow, buttercup-like flowers in early spring. Typically found in moist woodlands.

Attribution: Uoaei1, CC BY-SA 4.0

Common Name: Lesser periwinkle

Scientific Name: Vinca minor

Origin: Europe, Southwest Asia

Description: Lesser periwinkle is a trailing evergreen perennial that forms dense mats of glossy, dark green, oval leaves. It produces attractive, violet-blue, five-petaled flowers in spring and sporadically throughout the growing season. Commonly used as a groundcover in gardens, it can escape cultivation and invade forest understories, where it suppresses native vegetation. The plant spreads primarily through creeping stems that root at the nodes, allowing it to form extensive colonies. Seed production is rare and not a significant factor in its propagation.

Attribution: George Chernilevsky, Public domain, via Wikimedia Commons

Common Name: Mile-a-minute weed

Scientific Name: Persicaria perfoliata

Origin: East Asia

Description: Mile-a-minute weed is an annual, herbaceous vine that can grow up to 6 inches per day, reaching lengths of 20 feet. It has light green, triangular leaves and distinctive circular, leafy structures called ocreae that encircle the stem at nodes. The stems are covered with recurved barbs, aiding in climbing and attachment. It produces small, white flowers that give way to metallic blue berries. Typically found in open, disturbed areas, forest edges, and along waterways, it thrives in moist, sunny environments. The plant reproduces by seed, which are dispersed by birds, water, and human activities, leading to rapid colonization and displacement of native vegetation.

Attribution: Katja Schulz from Washington, D. C., USA, CC BY 2.0

Common Name: Morrow’s honeysuckle

Scientific Name: Lonicera morrowii

Origin: Japan

Description: Morrow’s honeysuckle is a deciduous shrub that can grow up to 6–10 feet tall, with opposite, oval, gray-green leaves. It produces pairs of tubular, white flowers that age to yellow, followed by red berries. Commonly found in forests, fields, and disturbed areas, it forms dense thickets that outcompete native vegetation. The plant reproduces by seed, with birds dispersing the berries, and can also spread vegetatively through its root system, facilitating its spread across suitable habitats.

Attribution: R.A.Nonenmacher, CC BY-SA 4.0

Common Name: Multiflora rose

Scientific Name: Rosa multiflora

Origin: East Asia

Description: Multiflora rose is a thorny, perennial shrub that can grow up to 10–15 feet tall and wide, with arching stems bearing pinnately compound leaves with 5–11 leaflets. It produces clusters of small, fragrant, white to pinkish flowers in late spring, followed by small, red hips. Typically found in fields, forests, and along roadsides, it forms dense thickets that displace native vegetation. The plant reproduces by seed, which are dispersed by birds and mammals, and can also spread vegetatively through rooting at the tips of arching canes, facilitating its rapid expansion in various habitats.

Attribution: Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0

Common Name: Norway maple

Scientific Name: Acer platanoides

Origin: Europe, Western Asia

Description: Norway maple is a deciduous tree that can grow up to 40–60 feet tall, with a broad, rounded crown. It has opposite, palmately lobed leaves with milky sap and produces small, yellow-green flowers in early spring before leaf-out. The tree is commonly found in urban settings, forests, and disturbed areas, where it can outcompete native trees due to its dense canopy and shade tolerance. It reproduces by producing abundant winged seeds (samaras) that are wind-dispersed, facilitating its spread into natural areas.

Attribution: Josep Gesti, CC BY-SA 4.0

Common Name: Oriental bittersweet

Scientific Name: Celastrus orbiculatus

Origin: East Asia

Description: Oriental bittersweet is a deciduous, woody vine that can climb up to 60 feet high or sprawl along the ground. It has alternate, round to oval leaves with finely toothed margins and produces clusters of small, greenish-yellow flowers in spring. In fall, it bears conspicuous yellow-orange capsules that split open to reveal bright red seeds. Typically found in forests, fields, and disturbed areas, it thrives in a variety of habitats. The plant reproduces by seed, which are dispersed by birds and mammals, and can also spread vegetatively through root suckers, leading to the formation of dense thickets that smother native vegetation.

Attribution: Jil Swearingen, USDI National Park Service, Bugwood.org

Common Name: Parrot-feather

Scientific Name: Myriophyllum aquaticum

Origin: South America

Description: Parrot-feather is a perennial aquatic plant with feathery, bright green leaves arranged in whorls around the stem. It can grow both submerged and emergent, with emergent stems extending up to a foot above the water surface. Typically found in ponds, lakes, and slow-moving water bodies, it forms dense mats that can impede water flow and outcompete native aquatic vegetation. The plant primarily propagates vegetatively, as fragments can root and establish new colonies, facilitating its rapid spread in suitable aquatic habitats.

Attribution: Blake Bringhurst, CC0, via Wikimedia Commons

Common Name: Porcelain berry

Scientific Name: Ampelopsis glandulosa

Origin: East Asia

Description: Porcelain berry is a deciduous, woody vine that can climb up to 15–20 feet high or sprawl along the ground. It has alternate, simple leaves that are heart-shaped or deeply lobed, resembling grape leaves. The plant produces small, greenish-white flowers in summer, followed by striking berries that mature to shades of blue, purple, and turquoise. Commonly found in forest edges, roadsides, and disturbed areas, it thrives in a variety of habitats. The plant reproduces by seed, which are dispersed by birds and mammals, and can also spread vegetatively through root suckers, leading to the formation of dense thickets that smother native vegetation.

Attribution: Jil Swearingen, USDI National Park Service, Bugwood.org

Common Name: Purple loosestrife

Scientific Name: Lythrum salicaria

Origin: Europe, Asia, Northwest Africa

Description: Purple loosestrife is a perennial herb that can grow up to 3–7 feet tall, with a square stem and lance-shaped leaves arranged oppositely or in whorls. It produces dense spikes of magenta flowers from mid to late summer. Typically found in wetlands, marshes, and along waterways, it thrives in moist soil conditions. The plant reproduces by seed, producing millions of tiny seeds annually that are dispersed by wind and water, facilitating its rapid spread and displacement of native wetland vegetation.

Attribution: Bjoertvedt, CC BY-SA 3.0

Common Name: Tatarian honeysuckle

Scientific Name: Lonicera tatarica

Origin: Central Asia, Siberia

Description: Tatarian honeysuckle is a deciduous shrub that can grow up to 10–12 feet tall, with spreading branches and ovate to oblong leaves. It produces pairs of tubular, white to pink flowers in spring, followed by red to orange berries. Commonly found in forests, fields, and disturbed areas, it forms dense thickets that outcompete native vegetation. The plant reproduces by seed, with birds dispersing the berries, and can also spread vegetatively through its root system, facilitating its spread across suitable habitats.

Attribution: Shadowmeld Photography, CC BY-SA 4.0

Common Name: Tree of heaven

Scientific Name: Ailanthus altissima

Origin: China, Taiwan

Description: Tree of heaven is a rapidly growing deciduous tree that can reach heights of 60–80 feet, with smooth, gray bark and large, pinnately compound leaves. It produces clusters of small, yellow-green flowers in late spring, followed by winged seeds called samaras. Typically found in urban areas, disturbed sites, and along roadsides, it thrives in a variety of soil conditions. The plant reproduces by seed, producing large quantities that are wind-dispersed, and can also spread vegetatively through root suckers, leading to the formation of dense stands that displace native vegetation.

Attribution: Luis Fernández García, CC BY-SA 4.0

Common Name: Water hyacinth

Scientific Name: Eichhornia crassipes

Origin: South America

Description: Water hyacinth is a free-floating perennial aquatic plant with glossy, rounded leaves and striking lavender to pink flowers arranged in spikes. Its spongy, bulbous stalks enable it to float on water surfaces. Typically found in ponds, lakes, and slow-moving water bodies, it forms dense mats that can impede water flow, block sunlight, and deplete oxygen levels, harming aquatic ecosystems. The plant reproduces by seed and vegetatively through daughter plants, facilitating rapid spread in suitable aquatic habitats.

Attribution: Trương Minh Khải, CC BY-SA 4.0

Common Name: Wineberry

Scientific Name: Rubus phoenicolasius

Origin: East Asia

Description: Wineberry is a deciduous shrub that can grow up to 6–9 feet tall, with arching, thorny stems covered in reddish hairs. It has trifoliate leaves with white undersides and produces small, white flowers in late spring, followed by red, raspberry-like fruits. Typically found in forests, fields, and along roadsides, it forms dense thickets that outcompete native vegetation. The plant reproduces by seed, which are dispersed by birds and mammals, and can also spread vegetatively through its arching canes that root at the tips, facilitating its spread across suitable habitats.

Attribution: Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0

Common Name: Yam-leaved clematis

Scientific Name: Clematis terniflora

Origin: Asia, Africa

Description: Yam-leaved clematis (Clematis terniflora), also known as sweet autumn clematis, is a vigorous, deciduous, twining vine native to Japan and China. It can climb structures or sprawl along the ground, reaching lengths of 15 to 30 feet. The plant produces an abundance of small, fragrant white flowers in late summer to early autumn, followed by feathery seed heads. It thrives in full sun to partial shade and adapts to various soil conditions. Sweet autumn clematis propagates through self-seeding, layering, and runners, allowing it to form dense mats that can smother native vegetation. Due to its aggressive growth and ability to invade natural areas, it is considered invasive in several U.S. states, including Delaware.​

Attribution: Alpsdake, CC BY-SA 4.0

Common Name: Yellow flag iris

Scientific Name: Iris pseudacorus

Origin: Europe, North Africa, Western Asia

Description: Euonymus alatus, commonly known as burning bush, is a deciduous shrub native to northeastern Asia. It typically grows between 5 to 10 feet tall, occasionally reaching up to 20 feet, and is characterized by its distinctive corky winged stems and vibrant red foliage in the fall University of Maryland Extension. Introduced to North America in the 1860s as an ornamental plant, it has become invasive, spreading into forests, fields, and roadsides Go Botany. The plant thrives in a variety of soil conditions and light exposures, from full sun to deep shade The Morton Arboretum. Its primary mode of propagation is through seeds dispersed by birds, which consume its red fruits and facilitate its spread across diverse habitats Go Botany.​

Attribution: George Chernilevsky, Public domain, via Wikimedia Commons

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