Polygonum erectum is an annual plant species with upright or ascending stems. It is a common weed in disturbed locations with dry soils in the North Eastern USA where it is called erect knotweed. It was once cultivated for food by Native Americans as part of the group of crops known as the Eastern Agricultural Complex.
Plants grow 10 to 50-(75) cm tall with many to few, non wiry branches. The leaves have distinct veins and entire edges or have jagged cut edges. The pedicels are shorter or equal the length of the calyx and typically longer than the ocreae. The closed flowers have a calyx that is typically 3 mm long, green in color and 5-lobed. Flowers in clusters of 1 to 5 in cymes that are produced in the axils of most leaves. The calyx segments are unequal with the outer lobes longer and not keeled and the inner ones narrowly keeled. The tepals are greenish, with yellowish tinting or sometimes with whitish tints. The seeds are produced in fruits called achenes that can be of two different types; one type is dark brown in color with a shiny surface and is broadly ovoid in shape, typically 2.5 mm long. The other achene type is dull brown in color, exsert and ovoid in shape, and 3–3.5 mm long. Late season fruiting is uncommon and if produced the achenes are 4 to 5 mm long.
- Gleason, A., Henry (1963). The new Britton and Brown illustrated flora of the northeastern United States and adjacent Canada. New York Botanical Garden by Hafner Pub. Co. pp. 72–84. LCCN 63016478.
- Polygonum erectum in Flora of North America @ efloras.org
- PLANTS Profile for Polygonum erectum (erect knotweed) | USDA PLANTS