Pennsylvania Smartweed

(Polygonum pensylvanicum)

Pennsylvania Smartweed (Polygonum pensylvanicum L.)

Identification: Flowers pink (sometimes white), small, arranged in tightly packed spikes. Stem swollen at the junction of a leaf and the stem, and with a papery sheath around the stem. Upper margin of the sheath without a fringe of hairlike spines. Swollen nodes usually reddish. Stem with small, glandular hairs. Leaves elongate, narrow, tapering toward both the base and the apex and shiny. Plant 1 to 4 feet in height.

Distribution: Throughout most of North America except for the Pacific Northwest.

Habitat: Pennsylvania Smartweed is found along roadsides, fields, and lawns.

Flowering period: June to October.

Similar Species: Pennsylvania Smartweed is most easily mistaken for Lady's Thumb. Lady's Thumb has a distinct fringe of hair-like spines on the upper margin of the sheath near the swollen joints of the stem. In addition the leaves of Lady's Thumb usually have dark blotches. Pale Smartweed is a taller species, with more elongate, pointed flower spikes with white flowers. The sheaths of both Long-bristled Smartweed and Mild Watter Pepper have spiny sheaths. The flower spikes of Mild Water Pepper are sparser than those of Pennsylvania Smartweed, and usually have interruptions along its length.