Family Polygonaceae (Knotweed Family).
A tiny weed found in lawns and sidewalk cracks and other places where weeds must be short to survive. The little white flowers sit in the leaf axils; if you look very closely, you will see the attractive green stripes on their petal-like sepals. In fact this is a plant worth a close look.
Gray describes the genus and the species:
POLYGONUM [Tourn.] L. KNOTWEED. Calyx 4–6(mostly 5)-parted; the divisions often petal-like, all erect in fruit, withering or persistent. Stamens 3–9. Styles or stigmas 2 or 3; achene accordingly lenticular or 3-angular. Embryo placed in a groove on the outside of the albumen and curved halfway around it; the radicle and usually the cotyledons slender. Pedicels jointed.—Ours all herbaceous, with fibrous roots (except in P. viviparum, flowering through late summer and early autumn. (Name composed of poly, many, and gony, knee, from the numerous joints.)
Achenes nearly or quite included by the fruiting calyx.
Branches terete or nearly so.
Flowers larger, the pedicels exserted; sepals (often 6) 2–3 mm. long.
Leaves elliptical, yellowish green, obtuse.
P. eréctum. Stout, erect or ascending, yellowish-green; leaves elliptical, 1.2–6 cm long, usually obtuse; flowers yellowish-green, about 3 mm. long, on more or less exserted pedicels; stamens 6–6; achene dull, included. —Waysides, waste places, etc.
