Smart-weed. Polygonum Hydropiper L. Achene dull, granular, light to dark reddish brown, lenticular, acutely and narrowly or broadly elliptical, or 3-sided, apex acute, concave on the sides, angles obtuse, 2–3 mm. long, sometimes with the remains of the dotted calyx attached. Introduced from Europe. Wet land.

Fig 35. [Dock-leaved or Pale Persicaria. Polygonum lapathifolium] L.

Dock-leaved or Pale Persicaria. Polygonum lapathifolium L. Achene shining, dark to chestnut brown, 2–2.2 mm. long, flattened, circular to broadly ovate with abruptly pointed apex, the base obtuse or bearing the remains of the thin calyx. Introduced from Europe. Low wet places.

Shore Knotweed. Polygonum littorale Link. So far as the achenes are concerned, they are identical with those of P. aviculare above described. Native of this country. On hard or thin places, especially when newly graded.

Fig 36. [Pennsylvania Persicaria, Polygonum Pennsylvanicum] L.

Pennsylvania Persicaria, Polygonum Pennsylvanicum L. Achene shining, jet-black, flattened, surface very slightly uneven and granular nearly circular with a short abrupt apex, edge rounded, 2.5–3 mm. long, often bearing the remains of the calyx. Native to this country. Occasional in annual crops.