Herbs or shrubs or woody climbers. Leaves alternate or rarely opposite, simple, entire or serrulate. Stipules thin, scarious or membranous, forming a sheath round the stem. Flowers small, regular, usually hermaphrodite, herbaceous or coloured, often jointed on the pedicel, clustered in the axils of the leaves or in page 588spikes or racemes, often forming terminal panicles. Perianth inferior, persistent; segments 3–6, free or connate at the base, imbricate. Stamens 5–9, rarely more or less, hypogynous or perigy-nous; filaments capillary or subulate, free or connate at the base; anthers 2-celled. Ovary superior, compressed or 3-gonous; styles 1–3; ovule solitary, basal, orthtropous. Fruit a small hard inde-hiscent trigonous or compressed nut, usually enclosed in the persistent perianth. Seed erect, testa membranous; albumen copious, farinaceous; embryo variable in position, radicle superior.

A rather large order, spread over the whole world, but most abundant in the north temperate zone. Genera 30; species over 600. The roots of many species are nauseous and purgative, the medicinal rhubarb being a well-known instance. On the other hand, the stems and leaves are frequently acid and refreshing, as the garden-rhubarb and the common sorrel. Buckwheat (Fagopyrum) is the only edible plant of any consequence. Of the 3 New Zealand genera, Muehlen-beckia extends to Australia and South America; the remaining 2 are widely distributed in both hemispheres.

Flowers hermaphrodite. Perianth-segments 5, not succulent in fruit	1. Polygonum.
Flowers hermaphrodite. Perianth-segments 6, the 3 inner enlarging and closing over the fruit, not succulent	2. Rumex.
Flowers unisexual. Perianth-segments 5, enlarged and succulent in fruit	3. Muehlenbeckia.