Polygonaceae is a family of flowering plants also known as the "knotweed family" or "smartweed family". The name is based on the genus Polygonum. Some well known members include Fagopyrum (buckwheat), Rumex (sorrel), Rheum (rhubarb), and Polygonum (knotgrass). The family is named for the many swollen node joints that some species have; poly means many and goni means knee or joint, though some interpret goni to mean seed, and the name then would refer to the many seeds these plants often produce.
According to the database of the Royal Botanic Gardens, Kew, the family consists of 43 genera, totalling about 1100 species. Numerically the most important are Eriogonum (250 species), Polygonum (200 species), Rumex (200 species), Coccoloba (120 species), and Calligonum (80 species).
The family is present worldwide, but are most differentiated in temperate regions.
Polygonaceae can be divided in two subfamilies:
Leaves of Polygonoideae are simple, arranged alternately on the stems and have a peculiar pair of sheathing stipules known as ocreae. Those species that do not have the nodal ocrea can be identified by having involucrate flower heads. The calyx is petaloid, often in two rows. The flowers are normally bisexual, small in size, actinomorphic with calyces of 3 or 6 imbricate sepals. After flowering the sepals often become membranous and enlarge around the developing fruit. Flowers lack a corolla and the sepals are petal-like and colorful. The androecium is composed of 3 to 8 stamens that are normally free or united at the base. Flowers with compound pistils composed of three united carpels with one locule - producing a single ovule. The ovary is superior with basal placentation, and 2 to 4 stigmas are produced.