Prostrate knotweed (Wireweed, Common knotgrass, Hogweed)
Polygonum aviculare (Polygonum heterophyllum)

Annual, seed-propagated weed with spindle-shaped root. Depending on location P. aviculare is extremely various in habit and leaf form.

Prostrate growth, mostly branching from base, small leaves.

Cotyledons: Very long, evenly slender, bluntly pointed.

Stems: Usually prostrate, heavily ramified, leaves at the nodes up to the tip, up to 50 cm (19.5 inch) long.

Leaves: Elliptical or lanceolate to linear, pinnate-nerved, hardly petiolate, emerging from a thin, membranous, stalk-enclosing, incised tube (stipule sheath).