Polygonum pensylvanicum L.
Polygonaceae (Smartweed family)
Erect summer annual.
Cotyledons are narrow oval to lance-shaped with rounded tips. Leaves are alternate, lance-shaped with pointed tips and smooth margins, usually hairless and occasionally with a purple watermark.
Branched, erect up to 4 feet tall and jointed with swollen nodes. A smooth, membranous sheath (ocrea) surrounds the stem at the base of each petiole.
Flowers and fruit
Small, pink to white flowers form in dense, spikelike clusters at the tips of stems. The seed is enclosed in a single-seeded, flat, glossy black, round to oval fruit with a pointed tip.
Ladysthumb (P. persicaria L.)
Differs by having a fringe of bristly hairs at the top of the ocrea. Usually has a purple watermark on leaf.
Pale smartweed (P. lapathifolium L.)
Differs by having young leaf undersides with whitish hair, older leaf undersides with yellow glands and a nodding inflorescence.
Swamp smartweed (P. amphibium var. emersum Michx.)
Differs by having perennial, creeping, woody rhizomes and usually hairy foliage; found in wetter environment.