Overview

The Polygonaceae are a family of flowering plants commonly known as the knotweed or buckwheat family. Members are most often herbs, though shrubs and a few tree-like or climbing species occur. Botanists recognize roughly thirty genera and about one thousand species, distributed worldwide but most diverse in temperate regions. For a basic reference on names and relationships see Polygonaceae resources.

Key characteristics

Plants in this family share several distinctive structural traits. Leaves are simple and usually alternate, and many species possess a distinctive stipular sheath that wraps around the stem at the leaf base; this sheath is called an ocrea and is a diagnostic feature. Flowers are typically small, actinomorphic, and arranged in clusters; perianths are usually formed of undifferentiated tepals rather than separate petals and sepals. The fruit is commonly an achene (a dry, single-seeded fruit).

Notable genera and uses

Several Polygonaceae species are important to people for food, horticulture, or ecological reasons. Examples include:

  • Fagopyrum (buckwheat) — cultivated for its nutrient-rich seeds that are used like cereal grains.
  • Rumex (sorrels and docks) — some species yield edible leaves, while others are common weeds.
  • Rheum (rhubarb) — grown for its edible leaf stalks in cooking and confectionery; see general information about rheum at Rheum and rhubarb.
  • Polygonum, Fallopia and related genera — include species often called knotweeds; a few are valued ornamentals, others are aggressive invaders.

History, taxonomy and notable facts

The family has a long history of study and has undergone revisions as botanists applied modern classification methods. Some groups once included in a broad concept of Polygonum have been split into smaller genera, reflecting finer distinctions in morphology and genetics. Ecologically, Polygonaceae species occupy a wide range of habitats from disturbed ground to alpine meadows. A number of knotweeds are known as invasive outside their native ranges and can alter riverbanks, roadsides, and built environments.

Because the family includes both cultivated crops and troublesome weeds, it is of interest to agronomy, horticulture, and conservation. Identification typically relies on the presence of the ocrea, leaf arrangement, flower structure, and fruit type, which together help separate Polygonaceae from superficially similar plant families.