This is an annual which reaches 30 to 50 cm high. The stems are square and covered with bristly hairs with some branching, arising from leaf axils. There is a characteristic swelling below the leaf joints. It is in the Mint Family and resembles the Stinging Nettle, but apart from the roughness of the stems, it does not sting. Infact the leaves are astringent and can be used to sooth sunburn and other itchy skin conditions. The leaves are also similar to those of the Nettle.
The flowers appear from July to September ad can be white or pink The seed are quite persistent and remain viable for several years, it can be a nuisance in cultivated ground if it is allowed to go to seed for a few seasons. The Bifid Hemp-nettle (Galeopsis bifida) is closely related and thought to be a subspecies, the only difference is a shorter corolla with a notch in the lip of the flowers of G. bifida.
Hoe or hand pull before flowering, easily uprooted.
Weedkillers to use:-
A contact herbicide such as Paraquat or a systemic such as Glyphosate kills the whole plant.
Residual herbicides prevent germination on paths and gravel.

See also Stinging Nettle and Hedge Woundwort which have similar leaves.