Curled dock, yellow dock
Description: A perennial dock growing to a metre tall. Leaves are long and parallel-sided with wavy margins; tap roots have a brown outer covering and are yellow within.
Habitat: Grassland, disturbed ground, farmyards, road verges, river banks, coastal shingle and mud.
Distribution: Common throughout the British Isles, and native to Europe and Africa, curled dock is one of the most widely distributed plants in the world.
Related species: The other common species is common or broad-leaved dock (R. obtusifolius), with which yellow dock hybridises.
Broad-leaved dock can be used interchangeably with curled dock – the thing to look for is a yellow root in either species, as that indicates the presence of the medicinal compounds.
Parts used: Root, dug up in autumn (provided it is yellow, use any species); leaves.