This plant is a bear to identify, specifically because there is a native knotweed, and an invasive one in Virginia, and the differences are, well, not that different as far as I’ve been able to tell. The chevron pattern on these leaves is striking.
Alternate Name: Jumpseed Size: 2-3' tall Family: Polygonaceae (Buckwheat Family) Habitat: Full to partial shade, on riverbanks, woods, cliffs, and rocks. Identification: "alternate leaves, with fine-hairy stipular sheaths (ocrea) with bristle-fringed edges which often turn brownish. Flowers, widely spaced along slender stalks, are white to greenish-white, rarely pink-tinged, and fruiting flowers have 2 downward-pointing hook-tipped styles. Persicaria virginiana is easily distinguished from most other Persicaria species by its much larger, more oval-shaped leaves, although a few species also have large leaves. It sometimes has a chevron-shaped marking on the leaves; often a single plant will have this marking on some leaves but not others." From wikipedia.com