Rumex californicus is a species of flowering plant in the knotweed family known by the common names willow dock and California dock. It is native to much of western North America and it can be found in parts of Europe as an introduced species and a roadside weed. It is an extremely variable plant which is generally divided into many varieties, some of which may actually be specimens of other species. In general, it is a perennial herb producing a slender stem which is prostrate and spreading or erect, growing up to about 90 centimeters in maximum length. The leaves are up to about 13 centimeters long and can be most any shape. The inflorescence is an interrupted series of clusters of flowers, with up to 20 in each cluster, each flower hanging from a pedicel. The flower has usually six tepals, the inner three of which are largest and usually have central tubercles. It is an important food and host plant for Lycaena rubidus larvae.
The Zuni people use the mexicanus variety medicinally. A strong infusion of the root is made and given to women by their husbands to help them to become pregnant. The ground root, or an infusion of it, is taken also for sore throat, especially by sword swallowers.