Photo: Polygonum aviculare 0.

Flowering patch. It's so common in the wild that I usually just ignore it. Here's a very lush patch, in a test plot for commercial cultivation. MTT Karila research station, Mikkeli, Finland. Planted. 2001-08-13.

Polygonum aviculare L.
Engl.: prostrate knotweed, knotgrass, knotweed.
Deu.: Vogelknöterich, Knotenwegerich, Wegtritt.
Suom.: pihatatar.
Sven.: trampört, trampgräs.
TCM: bian xu