spotted knapweed

not listed

NNA - Not applicable

SNA - Not applicable

not listed

Prohibited Noxious Weed, Prohibited – Control

Spotted knapweed is listed as an invasive terrestrial plant by the Minnesota Department of Natural Resources.

Spotted knapweed is a 12″ to 48″ tall, erect, biennial or short-lived perennial forb that rises on 1 to 20 stems from a stout taproot.

In the first year it produces a rosette of basal leaves. In the second year it sends up 1 to 20 leafy flowering stems.

The stems are erect or ascending, somewhat 4-angled but not winged, and branched at or above the middle. They are whitish- or grayish-green and rough to the touch due to a sparse covering of minute, short, stiff hairs. When young, they are also covered with short, soft, matted, woolly hairs, but these disappear quickly.

Basal leaves are inversely lance-shaped to elliptic in outline, up to 6″ long, and up to 2¾″ wide. They whitish- or grayish-green and are usually deeply pinnately divided into 2 to 4 pairs of lobes. The outermost leaves of the rosette may be undivided or have a few teeth.

Stem leaves are alternate. Lower stem leaves are stalkless or on short stalks and similar to basal leaves. Middle and upper stem leaves are mostly stalkless. The leaf blade either does not or only slightly extends down the stem. Middle stem leaves are deeply pinnately divided into several pairs of linear lobes, the lobes often again divided. The leaves become much smaller and less divided as they ascend the stem. Uppermost leaves are mostly unlobed, especially within the inflorescence. The upper surface and lower surfaces are rough to the touch due to a sparse covering of minute, short, stiff hairs. The margins are untoothed.

The inflorescence is a single ¾″ to 1″ in diameter flower head at the end of the stem and each branch. At the base of the flower head is an egg-shaped, ⅜″ to ½″ long, ¼″ to 5 ⁄16″ in diameter whorl of bracts (involucre). The bracts of the involucre are pressed closely together. They do not have sharp spines at the tip. They are green with dark brown to black tips and have a fringe of stiff, spreading or upward curved bristles. The bristles eventually turn black and have the appearance of eyelashes. The “eyelashes” are short, no more than half as long as the bract to which they are attached is wide.

There are numerous disk florets and no ray florets. The outermost disk florets are enlarged, sterile, and light purple to pinkish-purple. They may appear ray-like but closer examination shows them to be short tubes with 5 long lobes. The inner florets are white to pink and fertile.

The fruit is a brown or blackish-brown achene with a tuft of white, 1 ⁄32″ to ⅛″ long bristles at the tip.

12″ to 48″

Pink to purple

Dry. Roadsides, railroads, abandoned fields, ditches, disturbed sites. Full sun.

June to September

Sources

2, 3, 4, 5, 7, 22, 24, 28, 29, 30.

Native to Europe. Introduced and widely naturalized in North America.

Plant

Inflorescence

Flower Head

Location: Albany, NY