Invasives

Invasive, noxious, non-native- what’s the difference?

Invasive weeds are plants that dominate an ecosystem and spread rapidly once established, outcompeting native species, changing the composition of the habitat, and reducing overall biodiversity. According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), invasive species play a role in 60% of global plant and animal extinctions.

The term ‘noxious’ refers to a designation by a tribal, local, state, or federal authority of a plant as ‘injurious to public health, agriculture, recreation, wildlife or property’. The label allows land managers and owners to take action to curb or eradicate the species.

‘Non-native’ plants are plants from outside the given habitat; they are often invasive as they usually lack natural enemies and/or barriers to acquiring resources in their habitat. They can be planted intentionally, as in ornamental use, or accidentally through transport. Following the “Ten Percent Rule”, 10% of a given amount of non-native species introduced to a new habitat will survive, and 10% of these survivors will dominate (thus 1% overall). However, those that do dominate inflict incredible damage. Nevertheless, not every introduced species will have selective advantages over native flora and fauna and may work quite amiably in the habitat. Likewise, some native species can be considered invasive if they reproduce aggressively, overtake resources, and/or otherwise destabilize the ecosystem.

Specially regulated species, such as the Amur maple, have unique restrictions. They may be native and hold economic value, such as in ornamental settings, but they present environmental concerns and require specific management plans.

See below for a helpful graphic:

Invasives ID

Below are our most common invasives. Note: unless you have experience in removing non-native species, please do not attempt to eradicate them yourself. Not only may you accidentally spread the seed, but you may injure yourself, as a number of invasives are irritable or even toxic.

You can help expand this list by exploring the Natural Lands and adding observations to iNaturalist!

Western Poison Ivy (Toxicodendron rydbergii)

Photo credit: Robert Flogaus-Faust, CC BY 4.0

Key characteristics: Compound oval or egg-shaped leaves in groups of three, the end leaflet usually the only one stalked and the largest, so that all three form a T. Leaves can grow to be 6 inches long and 4 inches wide. Leaf groups on a plant are drooping and attached alternately to main woody stem. Leaves are hairless and untoothed or minutely toothed. Greenish-white flowers with yellow stamens extend in clusters from leaf axils. Poison ivy is an example of an invasive native (it was not brought from outside the area).

Habitat: Both dry and wet woodlands; riverbanks, streambeds, and marshes; disturbed areas (railroads, fence posts, urban settings); partial shade or full sun

Flowering Season: June-July

CAUTION: Poison ivy is a dermal irritant. Keep an eye out for it primarily in mature hardwood forests (but also in native prairies, suburban and urban areas, and along neglected corridors).

Garlic Mustard (Alliaria petiolata)

Photo Credit: Tony Atkin, CC BY-SA 2.0

Key characteristics: Coarsely toothed, kidney-shaped leaves (no more than 3 inches long and wide) that emit garlicky odor when crushed; flowering stalks have alternate, coarsely toothed leaves. Second year sees clusters of four-petaled white flowers. 1-2.5-inch slender seed pods contain a single row of many oval, black seeds.

Habitat: Moist, shaded areas such as floodplain forests and deciduous woods, and along trails/roads/fences; can tolerate full sun

Flowering Season: May-June

Birdsfoot Trefoil (Lotus corniculatus)

Photo Credit: Scot Magnotta, CC BY-NC 4.0

Key characteristics: Bright yellow flowers ½-inch long with upper petal erect and rounded at tip, clustered in groups of 3-12; compound leaves in groups of three extending from a stalk as long as the leaflets; leaves are dark green, oval or oblong, toothless and usually hairless, and widest at or above middle with pointed tip, tapering to base, from which egg-shaped outgrowths (stipules) nearly as large as the leaflets grow.

Habitat: Prairies and disturbed areas with full sun (often in ditches, waste areas, lawns, etc.); can adapt to a range of soil moistures

Flowering Season: June-August

Spotted Knapweed (Centaurea stoebe)

Photo Credit: Matt Lavin, CC BY-SA 2.0

Key characteristics: Thistle-like pink to purple flower heads, with long, narrow ray flowers on the outside and disk flowers in the flower’s center. Stems are stiff, hairy, and ridged. Leaves grow close to the ground in a clump in the first year and protrude as alternate, basal, gray-green to blue-green, deeply incised blades from the stem in the second year. Spotted Knapweed grows 2-3 feet tall.

Habitat: Prefers dry, sandy soils and sun; common along edges of native prairie, forests, fields, gravel pits, roads, railways, trails, and other disturbed areas

Flowering Season: June-October

Crown Vetch (Securigera varia)

Photo Credit: Peter Friedman, CC BY-NC-SA 4.0

Habitat: Partial shade to full sun; along fields, woodlands, pastures, roads, prairies, dunes, and streambanks

Flowering Season: May-September

Amur Maple (Acer ginnala)

Photo Credit: Daryl Mitchell (left), Anonymous (right), CC BY-SA 2.0

Key characteristics: Simple opposite leaves are 3-lobed, palmate, and double-toothed, with the center lobe being much wider than the outside two. Leaves are dark green until fall, when they turn yellow or red. Branches are slender, grayish-brown, and smooth. Bark is moderately furrowed, with a spreading, irregular crown. Shrub grows 15-20 feet tall. Fruit is a pair of 1 to 1 ¼ inch samaras.

Habitat: disturbed areas; urban and suburban landscapes; early successional forest, savanna, and open woodlands; tolerates full sun to partial shade and a range of soil moisture levels

Flowering Season: April-May

White Sweet Clover (Melilotus albus)

Photo Credits: Frank Mayfield (left) and Christophe Bornand (right)

Key characteristics: May grow tall and lanky or squat and bushy. Oblong gray-green leaves, rounded in the middle and wedge-shaped at the base, grow in groups of 3, sparsely distributed along stems. Leaves are slightly toothed and hairless. Middle leaflet has its own petiole. At the base of each leaf stalk is a pair of stipules (appendages) 3/8-inch long. Spike-like racemes of white flowers grow densely along branching stems. Stems are hairless and often ridged. Individual flowers are 1/4 inch long, pea-like, and drooping. Fruit is an oval pod with very short veins and 1-2 seeds.

Habitat: Open, sunny, disturbed areas with dry to moist soil such as roadsides, railroads, gravel pits, old fields, weedy meadows; also, prairies, shores, river banks, and woodland edges

Flowering Season: June-October

Yellow Sweet Clover (Melilotus officinalis)

Photo Credits: Anita Gould (left) and Peter Friedman (right), CC BY-NC 4.0

Key characteristics: May grow tall and lanky or squat and bushy. Alternate, gray-green leaves grow in groups of 3 and are diamond-shaped to lance-oblong, rounded in the middle and wedge-shaped at the base. Leaves are slightly toothed and hairless. Stems are hairless and often ridged. At the base of each leaf stalk is a pair of stipules (appendages) 3/8-inch long. Middle leaflet has its own petiole. Spike-like racemes of yellow flowers grow densely along branching stems; individual flowers are 1/4 inch long, pea-like, and drooping. Fruit is an oval pod with irregular, elongated veins and 1-2 seeds.

Habitat: Full or partial sun on disturbed, heavy soil; moist to mesic conditions; old fields, prairies, roadsides, railroads, gravel pits, weedy meadows, vacant lots, shores, river banks, woodland edges. Also thrives in high-quality habitat and in fire-affected settings.

Flowering Season: June-September

Can you tell the difference?

Below are our invasives that have a common non-invasive look-alike. Note similarities and distinctions.

Creeping Bellflower (Campanula rapunculoides) (REMOVE) vs American Bellflower (Campanulastrum americanum) (KEEP)

Photo Credits: Peter O’Connor (left) and Mary Crickmore (right)

Key differences: Both plants have alternate, slightly hairy, rough-textured, and coarsely toothed lance-like leaves, have five-lobed flowers, and produce a milky “sap” when broken. Creeping Bellflower flowers consist of nodding bells with pointed violet lobes that bloom on only one side of the stem, however. American Bellflower, meanwhile, produces not purple bells but blue star-shaped flowers with a white center ring that bloom on all sides of the stem. Creeping Bellflower also has a very extensive, spreading root system, a big reason it is so problematic.

CB Habitat: Shade or sun; disturbed areas, such as roadsides; deciduous woods and fields of mesic conditions, with loamy soil

AB Habitat: Partial shade; moist open woods or meadows, shady streambanks, thickets; mesic to wet conditions with rich, loamy soil

CB Flowering Season: June-October

AB Flowering Season: July-September

Reed Canary Grass (Phalaris arundinacea) (REMOVE) vs Canada Bluejoint (Calamagrostis canadensis) (KEEP)

Photo Credits: iNat user jdmd264 (first), Olivia Hebblewhite (all photos: second, third, and fourth slides)

Key differences: Reed canary grass is much taller, growing to be 6 feet tall while Canada bluejoint does not exceed 5 feet. Reed canary grass also has a more prominent midvein on the upper side of its leaf blade. The invasive’s blades are larger at 10-20 mm wide, and quite evenly spaced, while the natives’ blades are 2-10 mm wide. Reed canary grass has overlapping stem sheaths near the ligule (where the stem meets the sheath), and ligules are thin and translucent, while Canada bluejoint’s ligule is robust.

RCG Habitat: Partial shade to sun; moist (though it can tolerate dry) soil in wetlands, fields, and woods; along roadside ditches

CB Habitat: Partial to full sun; moist or wet soil of loam, clay, silt, or sand; sedge meadows, marshes, bogs, fens, swales, prairie

RCG Fruiting Season: late spring to early summer

CB Fruiting Season: July-August

Common Buckthorn (Rhamnus cathartica) (REMOVE) vs Various Prunus (Chokecherry, American plum, etc.) (KEEP)

Photo Credits: K. Chung (first) and Jessie Crow Mermel (second), CC BY-NC 4.0, Rebecca Jimenez Husted (third), CC BY-NC-ND 2.0

Key differences: While the berries of both Buckthorn and its look-alikes are usually dark and round, Prunus species have glands on the leaf petioles. Also, Prunus leaves are alternate, oblong-elliptic or ovate, and usually more pointed than Common buckthorn, while Common Buckthorn leaves are sub-opposite and egg-shaped. Common Buckthorn leaves also have veins that curve as they approach the leaf margin (arcuate venation).

Rhamnus c. Habitat: Full shade, partial shade, or sun; at disturbed edges such as fence rows, roadsides, and waste areas; dry to moist woods

Prunus Habitat: Temperate regions; partial shade, shade, sun; forests, shrublands, fields, riverbanks, roadsides

Rhamnus c. Flowering Season: June-July

Prunus Flowering Season: Variable (spring through summer)

Wild Parsnip (Pastinaca sativa) (REMOVE) vs Golden Alexanders (Zizia aurea) (KEEP)

Photo Credit: JD Youngfox (first), Christophe Bornand (second, CC BY-NC 4.0, Derek Ramsey (third), CC-BY-SA-2.5,2.0,1.0

Key differences: Stems of Golden Alexander are smooth and shiny, while those of Wild Parsnip are ridged. Both plants have compound leaves and yellow flower umbels. However, Wild Parsnip has groups of 5-15 large, directly opposite coarsely toothed leaflets while Golden Alexander has groups of three 2-3 inch finely toothed leaflets. Finally, Golden Alexander rarely exceeds three feet, while Wild Parsnip can grow to be six feet tall!

WP Habitat: Sun; mesic to moist soil; wet meadows, open fields, and ditches

GA Habitat: Partial shade to sun; fertile fields, thickets, and woods; along streams

WP Flowering Season: June-July

GA Flowering Season: May-July

CAUTION: Wild Parsnip is a major dermal irritant. Skin exposed to toxins in the sap will develop painful blisters and burns under any sunlight, a condition called “phytophotodermatitis”. Use PPE if and when removing it.

Queen Anne’s Lace (a.k.a Wild Carrot) (Daucus carota) (REMOVE) vs Poison Hemlock (Conium maculatum) (REMOVE, POISONOUS) vs Water Hemlock (Cicuta maculata) (POISONOUS, MAY KEEP)

Photo Credit: Jay Heiser (first slide, right) Peter Friedman (first slide, left), Amanda Kat (second slide, left), Alexander Baransky (second slide, right), Byron Murray, third slide, CC BY-NC 4.0

Key Differences: The leaves of all three are compound and deeply divided, and they share umbels of 5-petaled white flowers. However, those leaves of Queen Anne’s Lace are gray-green, slightly hairy, very skinny, and feather-like; those of Poison Hemlock are dark green, hairless, and triangular. Poison Hemlock’s leaves divide 2 to 4 times into wide, fern-like leaflets. Water Hemlock’s leaves divide 1 to 3 times into 1 to 4-inch-long narrow-toothed leaflets. Water Hemlock’s leaves are more pointed than its hemlock twin. Most notably, Water Hemlock’s leaflet veins run out from the central vein to the notch of the leaf’s teeth rather than the tip, and the plant has a hollow, bulbous root. Stems of both hemlocks are hairless and purple-spotted; stems of Queen Anne’s Lace are very hairy and ribbed. Both hemlocks have no bracts, while, at the base of the flowers, Queen Anne’s Lace’s has prominent umbel bracts lobed into long, skinny segments that curl like lace. Queen Anne’s Lace’s umbels cave upward and in, seeming to close shut, on the plant when approaching the end of its flowering. Finally, Water Hemlock grows 3 to 6 feet tall and Poison Hemlock grows 8 to 10 feet tall, while Queen Anne’s Lace only grows 2 to 3 feet tall.

QAL Habitat: Partial shade to sun; mesic to dry conditions; open fields and woodland edges; overgrown thickets, lawns, pastures; roadsides and waste areas

PH Habitat: Full sun with moist soil (can tolerate dry soil); marginal, disturbed areas like roadsides, utility corridors, ditches, fence rows, abandoned fields, railroads; also, streams, meadows, marshes, and wetlands

WH Habitat: Prefers full sun (tolerates partial shade) near water; along ditches, streambeds, pond edges, swamps, fens, and the low-lying, wet areas of pastures and meadows

QAL Flowering Season: June-September

PH Flowering Season: June-August

WH Flowering Season: June-August

NOTE: Both Queen Anne’s Lace and Poison Hemlock are non-natives and considered noxious weeds in Minnesota, and in fact Poison Hemlock is prohibited/restricted. Water Hemlock, while poisonous, is native. If not threatening humans and animals, Water Hemlock may be left alone.

CAUTION: All parts of Poison Hemlock and Water Hemlock are toxic, often inducing dermal irritation and fatal if ingested. Both hemlocks can kill sheep, cattle, and horses in 15 minutes to a matter of hours and cause reproductive defects. Take extreme care when removing.

Dame’s rocket (Hesperis matronalis) (REMOVE) vs Prairie phlox (Phlox philosa) (KEEP) and Woodland phlox (Phlox divaricata) (KEEP)

Photo Credit: Peter Friedman (first), Mark Kluge (second), and Aaron Lincoln (third), CC BY-NC 4.0

Key differences: Dame’s rocket has four petals while Prairie phlox and Woodland phlox have five. Plus, Dame’s rocket leaves are alternate; both the natives’ leaves are opposite.

DR Habitat: Full shade, partial shade, or sun; open, moist or mesic woodlands or plains; disturbed edges, such as woodland boundaries, thickets, roadsides, railroads, ditches, streams, or waste sites

WP Habitat: Partial or full shade; dense woodlands

PP Habitat: Partial to full sun; open, dry prairies and woods

DR Flowering Season: May-July

WP Flowering Season: April-June

PP Flowering Season: May-July

Asian Honeysuckles (Lonicera sp.) (REMOVE) vs Native Bush Honeysuckles (Diervilla sp.) (KEEP)

Photo Credit: Eric Hunt (first slide, left) and Biodiversity Heritage Library (first slide, right), Avery Allert (second slide), CC BY-SA 2.0

Key differences: Native bush honeysuckles, such as Northern Bush Honeysuckle, have solid piths, usually white, while nonnative honeysuckles have hollow stems with a brownish pith.

Honeysuckles can be difficult to distinguish. All produce red to orange berries. Native and non-native varieties may have leaves toothed or toothless, fine-haired or hairless, and egg-shaped to lance-elliptic. Flower color is variable as well (e.g Northern Bush Honeysuckle has pale yellow to orangish-red flowers, while the Amur Honeysuckle has white flowers).

Amur Honeysuckle Habitat (may vary across non-native honeysuckles): Partial shade to sun; marginal, disturbed areas; fields, forests

Northern Bush Honeysuckle Habitat (may vary across native honeysuckles): Partial to full shade to full sun; dry, rocky, and/or sandy conditions; thickets, woodlands, slopes, fields, ridges, bluffs

Amur Honeysuckle Flowering Season (may vary across non-native honeysuckles): May-June

Northern Bush Honeysuckle Flowering Season (may vary across native honeysuckles): June-July

Creeping Thistle (Cirsium arvense) (REMOVE) and Bull Thistle (Cirsium vulgare) (REMOVE) vs Field Thistle (Cirsium discolor) and other native thistles (KEEP)

Key differences: Both invasive thistles have very spiny, deeply lobed leaves, produce large purple flowers and dark green leaves, and grow to be 2-6 feet tall (Field thistle: 3 to 7 feet). However, Creeping thistle has spines neither under the flower heads nor on the main stem while Bull thistle has spikes (“wings) on the bracts and covering all the stems. Additionally, Creeping thistle has smaller flowers (1-2 cm wide) and leaves. Bull thistle leaves are broad, and reddish-purple, star-like flowers are 4-5 cm wide. The leaves of Field thistle are minutely spiny but stems are not; most importantly, the underside of most native thistles’ leaves, including Field thistle, are white and densely covered in small, fine hairs. Field thistle’s bracts also distinguish it: they are green with a white stripe and resemble fish scales, with a small pointed tip at each end, while those of Bull thistle are green, narrow, very spiny, and outward-growing, and those of Creeping thistle are flat but with pointed, purplish tips.

CT Habitat: Sunny, open areas in mesic conditions from floodplains, wetlands, lakeshores, forests, and savannah to degraded pastures, cropland, and roadsides

BT Habitat: Dry, open areas with mesic to moist conditions and disturbed soil, such as abandoned fields, roadsides, railroads, degraded lakeshores, logged forest and waste sites

FT Habitat: Sunny, open areas; moist to dry conditions; woodlands, roadsides, riverbanks, glades, pastures, meadows

CT Flowering Season: June-October

BT Flowering Season: June-October

FT Flowering Season: July-October

By: Olivia Hebblewhite

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