This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Annual. Propagates by seeds.
Time of bloom: June to September.
Seed-time: July to November.
Range: Throughout North America. Naturalized in the Eastern States, but indigenous in the Northwest.
Habitat: Low fields and meadows; gardens and barnyards, waste places.
The juice of this plant is exceedingly biting and pungent to the taste and will raise blisters when applied to the skin. It is not insistently a water-weed, as its name implies, but will grow where the soil is only moderately moist.
Stem smooth, erect, slender, with few branches, ten inches to two feet tall, light green or frequently of a reddish color. Leaves narrow lance-shaped, one to four inches long, with short petioles, the surface dotted with glands, the edges entire or slightly wavy, ciliate, the sheathing stipules cylindric and fringed with short bristles. Flowers in slender, nodding, interrupted racemes; calyx greenish, also gland-dotted, and as pungent to taste as the leaves; stamens four to six; style short, two- or three-parted. Achenes minutely ridged, lens-shaped or three-angled approaching to ovoid, dull, reddish brown. (Fig. 60.)
Fig. 60. - Common Smart-weed (Polygonum Hydropiper). X 1/4.
Cultivation of the ground; close cutting or hand-pulling before the earliest flowers ripen seed.