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Polygonaceae

Knotweed family of flowering plants

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  • 4 chapters
Polygonum persicaria flowers and leaves
Bogdan Giuşcă · CC BY-SA 3.0

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The Polygonaceae comprise about 1,200 species distributed into about 48 genera. The largest genera are Eriogonum (240 species), Rumex (200 species), Coccoloba (120 species), Persicaria (100 species) and Calligonum (80 species). The family is present worldwide, but is most diverse in the North Temperate Zone.

Several species are cultivated as ornamentals. A few species of Triplaris provide lumber. The fruit of the sea grape (Coccoloba uvifera) is eaten, and in Florida, jelly is made from it and sold commercially. The seeds of two species of Fagopyrum, known as buckwheat, are eaten in the form of groats or used to make flour. The petioles of rhubarb (Rheum rhabarbarum and hybrids) are a food item. The leaves of the common sorrel (Rumex acetosa) are eaten in salads or as a leaf vegetable.

Polygonaceae contain some of the most prolific weeds, including species of Persicaria, Rumex and Polygonum, as well as Japanese knotweed.

Taxonomy

Polygonaceae are very well-defined and have long been universally recognized. In the APG III system, the family is placed in the order Caryophyllales. Within the order, it lies outside of the large clade known as the core Caryophyllales. It is a sister to the family Plumbaginaceae, which it does not resemble morphologically.

The last comprehensive revision of the family was published in 1993 by John Brandbyge as part of The Families and Genera of Vascular Plants. Brandbyge followed earlier systems of plant classification in dividing Polygonaceae into two subfamilies, Eriogonoideae and Polygonoideae. Since 1993, the circumscriptions of these two subfamilies have been changed in light of phylogenetic studies of DNA sequences. Genera related to Coccoloba and Triplaris were moved from Polygonoideae to Eriogonoideae. The genus Symmeria does not belong to either of these subfamilies because it is a sister to the rest of the family. Afrobrunnichia might constitute a new subfamily as well.

Brandbyge wrote descriptions for 43 genera of Polygonaceae in 1993. Since then, a few more genera have been erected, and some segregates of Brunnichia, Eriogonum, and Persicaria have been given generic status in major works. Some of the genera were found not to be monophyletic and their limits have been revised. These include Ruprechtia, Eriogonum, Chorizanthe, Persicaria, Aconogonon, Polygonum, Fallopia, and Muehlenbeckia.

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