Guide to Common Invasives

by Pam Cowher and Dan Dixon

Canada Thistle (Cirsium arvense)

    • aster family
    • 1.5 —4 feet tall
    • prickly lance shaped leaves
    • stems branched, somewhat hairy and ridged
    • lavender or white flowerheads (June — October)

<www.noble.org/imagegallery/grassshtml/CommonReed.html>

Common Reed (Phragmites australis)

    • Commonly found in wetlands
    • Perennial grass
    • Towering height — up to 14 feet
    • Stiff, wide leaves
    • Hollow stem
    • Clusters of tiny purplish flowers (July — October)

<www.nps.gov>

Dame’s Rocket (Hesperis matronalis)

    • showy but short-lived perennial
    • large loose clusters of white, pink or purple flowers (May — August)
    • 2 to 3 feet in height
    • leaves oblong, sharply toothed and alternately arranged
    • Flowers have 4 petals

<www.nps.gov>

Garlic Mustard (Alliaria petiolata)

    • Cool season biennial herb
    • Mustard family
    • Stalked, triangular to heart shaped coarse toothed leaves
    • Produces garlic order when crushed
    • Mature flowering plants reach 2 to 3.5 feet in height
    • Small white clusters of flowers
    • Flowers have 4 petals and are cross-shaped
<www.appliedvegetationdynamics.co.uk/hogweed/>

Giant Hogweed (Heracleum mantegazzianum)

    • Parsley or mustard family
    • May grow 15 to 20 feet tall
    • Closely resembles common hogweed except for size
    • Stout, dark reddish-purple stem
    • Spotted leaf stalks that are hollow and produce sturdy bristles
    • Numerous white flowers clustered in umbrella-shaped head (May — July)

<www.inasive.org/weeds/JH.html>

Japanese Honeysuckle (Lonicera japonica)

    • Semi-evergreen woody vine
    • Opposite leaves, ovate to elliptic to oblong
    • High climbing to 80 feet long
    • Often forms arbors throughout forest
    • Stem is slender, brown and hairy
    • Flowers April to June

<www.nps.gov>

Japanese Knotweed (Polygonum cospidatum)

    • Member of buckwheat family
    • Upright, herbaceous perennial
    • Can grow over 10 feet in height
    • Smooth, stout and swollen at joints where leaf meets stem
    • Stalk is similar to bamboo
    • Leaf broad oval to somewhat triangular and pointed at tip
    • Greenish-white flower, branched spray

<www.vet.purdue.edu/depts/addl/toxic/plant43.htm>

Johnson Grass (Sorghum halepense)

    • Coarse perennial grass
    • Large, scaly root stems
    • Dense stands up to 6 feet tall
    • Seed heads large and loose
    • Toxic to animals when eaten

<www.nps.gov>

Mile-a-Minute Vine (Polygonum perfoliatum)

    • Herbaceous annual trailing vine
    • Buckwheat family
    • Reddish stems with downward pointing barbs
    • Leaves alternate and shaped like equilateral triangles
    • Circular, cup-shaped leafy structure surrounds stem
    • Flowers small white and inconspicuous

<www.nps.gov>

Multiflora Rose (Rosa multiflora)

    • Thorny, perennial shrub
    • Arching stems
    • Leafs divided into 5 to 11 sharply toothed leaflets
    • Clusters of showy, fragrant white to pink flowers beginning in May or June

<www.nps.gov>

Purple Loosestrife (Lythrum salicaria)

    • Erect perennial herb
    • Loosestrife family
    • Square woody stem
    • Opposite or whorled leaves
    • Leaves lance-shaped, stalkless and heart shaped or rounded at base
    • Grows 4 to 10 feet high depending on conditions
    • Magenta colored flowered spikes thought summer
    • Flowers have 5 to 7 petals

<www.nps.gov>

Tree of Heaven (Ailanthus altissima)

    • Mature trees can reach 80 feet in height
    • Smooth stems with pale gray bark
    • Twigs light chestnut brown
    • Large compound leaves 1 to 4 feet in length
    • Strong offensive odor some have likened to peanuts or cashews
    • Often confused with sumac