Polygonum arenarium

About

Polygonum arenarium, the lesser red-knotgrass or European knotweed, is a species of flowering plant in the family Polygonaceae. It is native to Morocco, France, the former Czechoslovakia, Hungary, southeastern and eastern Europe, the Caucasus, Turkey, the Levant, Iraq, Iran, and Central Asia, and it has been introduced to Argentina, the British Isles, Germany, the Baltic States, and central European Russia. A scrambling or procumbent annual, it is often found in disturbed habitats. In more natural situations it is a psammophyte.

Summary from Wikipedia