Herb/forb, part of the buckwheat family. Invasive. Spreads out and grows flat along the ground, forming a ground cover. Flowers are too small to be seen and have colored sepals rather than petals. Each stem has a sheath at the node. Leaf shape is generally elliptical but can vary depending on moisture.
Oregon State University. http://oregonstate.edu/dept/nursery-weeds/weedspeciespage/prostrate_knotweed/knotweed_page.htm
|Disturbed, mesic soils.||Partial sunlight||Yes|