This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Herbs (or rarely shrubs) with alternate simple leaves and sheathing often fringed stipules. Flowers usually hermaphrodite, on jointed pedicels. Perianth inferior, composed of 3 to 6 petaloid or green, free or united, persistent segments, imbricate in bud. Stamens 3 to 12, or more. Fruit a dry 1-celled 1-seeded indehiscent achene or nut, usually enveloped in the perianth. Seeds erect, albuminous. This order comprises about 30 genera and 500 species, found in all regions, but most abundantly in the north temperate zone. The Docks and Knotweeds represent them only too well in this country.