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Polygonaceae (buckwheat, dock, rhubarb, sorrel) A family of herbs, with a few shrubs and trees, in which the leaves are simple, entire, and usually alternate. They have an unusual sheathing stipule known as the ochrea (or ocrea) at the leaf base. The flowers are bisexual, regular, and are usually held in a raceme if they are not solitary. They are white, green, or pinkish. The 3–6 sepals often form a membrane wing around the fruit. There are no petals, and 6–9 stamens. The ovary is superior, with 2–4 carpels which are united to produce a single locule with free styles. The fruit is a trigonous nut with a seed containing a copious endosperm. The seeds are often dispersed by wind with the aid of the calyx wing; other seeds are hooked. The family is closely related to the Plumbaginaceae and is separated into 3 groups based on the geographical zone in which they are distributed;
a. the tropical, half-hardy, climbing trees and shrubs;

b. the shrubby buckwheats of arid habitats in south-eastern Europe, central Asia, and N. America; and

c. the temperate species, including the edible species (e.g. Rheum rhaponticum, rhubarb, and Fagopyrym esculentum, common buckwheat), the ornamentals (e.g. Muehlenbeckia species and Erigonum species), and the weeds (e.g. Rumex species, sorrels and docks). There are 51 genera, comprising about 1050 species, distributed throughout the world, but with a concentration in the northern temperate regions.