Invasive Plants-Spotted Knapweed

Invasive Plant Species on the Wolf Hill Property

Spotted Knapweed (Centaurea biebersteinii
Aster family (Asteraceae)


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Key Characteristics

Biennial herb grows in tufted clumps, 1’-3’ H, most branching occurring in the upper half of plants.
Pinnately to bipinnately dissected leaves 4” - 8” L.
Flowers are white to pink or purple and grow at the end of the stems in thistle-like heads.

Habit

Biennial herb that grows in erect, tufted clumps, from 1’-3’ in height—one plant may give rise to up to twenty slender, upright stems, with most of the branching occurring in the upper half of the stem

Leaves

Seedlings form a rosette of alternate, pinnately to bipinnately dissected leaves 4-8 inches long
Stem leaves are pinnate, low on the stem and become smaller, and linear-shaped further up

Flowers

Fruit

Habitat

In dry sterile, gravelly, or sandy openings such as pastures, old fields, and roadsides.

Similar Species

If leaves shaped like a feather, with narrow lobes = C. bierbersteinii
If leaves entire or toothed, or some of the larger ones few-lobed, lower leaves over 1 cm wide = 1 of other 3 species
If dry tip of the bracts under the flower are tan to dark brown, the middle and outer bracts have jagged edges, inner bracts are expanded and often deeply cleft from the tip; the marginal flowers are generally enlarged and ray-like = C. jacea
If dry tip of the bracts under the flower are blackish at least in part, the middle and outer bracts are comb-like, and they are seldom deeply cleft = C. nigrescens or C. nigra
If tip of the bracts are small, 1-3mm; flower heads relatively narrow, generally higher than broad; marginal flowers are enlarged and ray like = C. nigrescens
If tip of the bracts are large, the larger ones 4-6 mm; flower heads are relatively broad, broader than high; the marginal flowers are not enlarged, except in a frequent hybrid with C. jacea = C. nigra