Tufted Knotweed

Polygonum caespitosum var .longisetum

Weed Description
A summer annual weed of horticultural, agronomic, and nursery crops that may reach 3 1/2 feet in height.

Seedlings
Cotyledons are elliptic to lanceolate in outline, whit hairs along the margins. First true leaves are alternate, lanceolate in outline, and hairy on the upper surfaces.

Leaves
Arranged alternately along the stem, lanceolate to elliptic in outline, approximately 3/4 to 3 inches long and 1/2 to 1 1/4 inches wide. Older leaves are usually only slightly hairy. Leaves taper to short petioles, which have an ocrea that encircles the stem. Leaves often, but not always, have a purple spot in the middle of the leaf.

Stems
Branched, often reddish in color and swollen at the nodes. A thin membranous sheath called an ocrea encircles the stem at the base of each leaf petiole. The ocreas of tufted knotweed have stiff hairs arising from the top of the ocrea, which are from 5 to 10 mm long.

Flowers
Flowers are clustered in terminal spikes at the ends of stems. Individual flowers are small and are dark pink to red in color.

Fruit
A black achene.

Roots
Fibrous roots with a shallow taproot.

Identifying Characteristics
The elliptic to lanceolate leaves with a purple spotted ladys thumb print in the middle and distinctive ocrea with stiff hairs are all characteristics that help to distinguish tufted knotweed from other similar weeds. Pennsylvania Smartweed (Polygonum pensylvanicum) is very similar in appearance and growth habit, but does not have hairs on the ocrea like that of tufted knotweed. Ladysthumb (Polygonum persicaria) is also similar in appearance and growth habit, but has hairs on the ocrea that are much shorter (2 mm) than those of ladysthumb, and also has generally smaller leaves and dark pink to red flowers.

Office of Programs

University of Missouri

Tufted Knotweed

Polygonum caespitosum var .longisetum