- Name also: Dooryard Dock
- Family: Dock Family – Polygonaceae
- Height: 60–120 cm (25–50 in.) Stem unbranched up to inflorescence. Stem erect through winter.
- Flower: Usually bisexual, small, 2–3 mm (0.08–1.2 in.) wide, regular. Perianth-segments in two whorls of three. Segments of outer whorl small and turned backwards. Inner whorl forms the fruit valves which are roundish to kidney-shaped, with entire or crenulate margins, and usu. without pimples. Sometimes one segment has an elongated pimple along the midrib. Stamens 6. Pistil consists of 3 fused carpels, styles 3. Joint on flower-stalk near base. Flowers in clusters in several racemes.
- Leaves: Basal leaves like in rosette, stem-leaves spirally. Basal leaves long-stalked (stalk as long as blade), stem-leaves short-stalked. Blade hairy on the underside along the veins, elongated–ovate to elliptic (not more than four times as long as broad), with rounded or tapered base and wavy margins. Ochrea membranous, fringed.
- Fruit: Brown, sharply three-edged, approx. 3 mm (0.12 in.) wide, glossy achene.
- Habitat: Arable land, roadsides, shores, gardens, rubbish tips.
- Flowering time: (June–)July–September.
Genus Rumex is a taxonomically difficult genus as the species hybridise frequently – Nothern dock with curled dock (R. cispus), broad-leaved dock (R. obtusifolius), Asiatic dock (R. confertus), Scottish dock (R. aquaticus) and field dock (Finnish dock, R. pseudonatronatus). The valves enclosing the ripe fruit are (often) essential to identification.
Northern dock is perennial. It belongs to an intrageneric section in which the flowers are bisexual and the fruit valves are clearly longer than the fruit. Northern dock is usually associated with human influence, and has spread with the help of man. It thrives on nitrogen-rich soil. It has been noted to avoid basic substrate.