Knotgrass n. : a common weed with jointed stems (Polygonum aviculare); knotweed.

Knotgrass n. : The dog grass. See under Dog.

Example:
Where can i buy Knotgrass/knotweed bian xu/Polygonum aviculare?

Taxonomy
Polygonum, species, smartweed, Persicaria, genus name, free encyclopedia, stem, polygonum cognatum, knotweed, thumb, Several species, Polygonum baldschuanicum, Polygonum japonicum, Polygonum coccineum, family Polygonaceae, Lepidoptera species, Turkey, dish.

Defination from the web:
knotgrass, bistort, tear-thumb, mile-a-minute, and several others. In the Middle English glossary of herbs "Alphita" (ca. ... Polygonum maritimum – sea knotgrass. Polygonum meisneranum. Polygonum meisnerianum. Polygonum minimum ...