# Polygonaceae
**Polygonaceae**, the buckwheat or knotweed family, is a family of flowering plants in the order [Caryophyllales](https://www.edgepedia.org/caryophyllales), characterized by swollen stem nodes, sheathing stipules called ocreae, small flowers with a perianth of (3)5 to 6 tepals usually in two whorls, and dry one-seeded fruits that are typically three-angled achenes or nuts. The name was published by Antoine Laurent de Jussieu in 1789 and is conserved (nom. cons.)[1](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2). The family is cosmopolitan, occurring from the Arctic to the tropical lowlands, with most of its genera and species in northern temperate regions[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). It includes buckwheat, rhubarb, and sorrel as food plants, and several invasive knotweeds[3](https://www.benthamscience.com/chapter/25539) • [2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information).
| Key fact | Detail |
|---|---|
| Scientific name | Polygonaceae Juss., first published 1789, nom. cons.; family accepted[1](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2) |
| Size | Estimates differ by authority: 55 genera and ca. 1,000 species in two subfamilies (Kew handbook); about 49 genera and 1,200 species (Trees of New Guinea); 57 accepted genera in Plants of the World Online[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information) |
| Signature character | Ocrea, a stipule-derived membranous sheath around the stem at each node, present in Polygonoideae and absent in Eriogonoideae[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information) |
| Flowers | Small, actinomorphic, usually bisexual; tepals (3)5–6 in two whorls, petals absent; stamens (1)6–9(–18)[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information) |
| Fruit | Indehiscent trigonous or lenticular achene or nut, often enclosed by a persistent, accrescent perianth[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information) |
| Distribution | Cosmopolitan, common in northern temperate regions; largest genera Polygonum (ca. 250 species), Rumex (ca. 200), Eriogonum (ca. 200), Persicaria (ca. 100), Calligonum (ca. 80)[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information) |
| Uses | Buckwheat seed and flour, rhubarb petioles, sorrel leaves; some species medicinal or ornamental[3](https://www.benthamscience.com/chapter/25539) |
## Vegetative morphology
Members are herbs, shrubs, climbers, or rarely trees, without latex[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). Leaves are simple and alternate, usually spirally arranged, with mostly entire margins[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). The stems often have conspicuously swollen nodes, which give the family its name: Polygonaceae means "many knees"[4](https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/polygonaceae).
The ocrea is the family's most distinctive structure: stipules are connate into a tubular, membranous or scarious sheath that encircles the stem above each leaf base[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). It is present in the subfamily Polygonoideae and absent in Eriogonoideae, and it may be reduced to a nodal ring in some species[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information) • [5](https://virtuelle-gaerten.uni-hohenheim.de/4DACTION/W_Init/HG_Family_en?HTID=HOH-3740). The ocrea separates Polygonaceae from superficially similar families: [Caryophyllaceae](https://www.edgepedia.org/caryophyllaceae) lack an ocrea, have opposite leaves, and usually have petals, while [Plumbaginaceae](https://www.edgepedia.org/plumbaginaceae) have swollen nodes but neither ocrea nor stipules[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information).
## Flowers and fruit
The flowers are small and inconspicuous, actinomorphic, and usually hermaphrodite, though some species are polygamous or dioecious[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). Petals are absent; the perianth consists of (3)5–6 tepals, free or united into a tube, usually in two whorls, and green, white, yellow, red, or purple[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). Stamens number (1)6–9(–18), with filaments free or forming a tube[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). The [gynoecium](https://www.edgepedia.org/gynoecium) has a superior ovary of 2–4 united carpels forming a single locule with one basal ovule, and 1–3(4) styles[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information).
The fruit is dry and indehiscent, usually a three-angled (trigonous) or flattened, lenticular achene or nut, winged or unwinged[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). The perianth is persistent and often accrescent, enlarging in fruit and sometimes becoming membranous, hard, or fleshy, so that the fruit is commonly enclosed by it; in some genera the fruit bears hooks, tubercles, wings, or barbed setae that aid dispersal[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information) • [6](https://www.delta-intkey.com/famfs/www/polygo.htm). Seeds contain abundant mealy or oily endosperm[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information).
## Phylogeny and classification
Molecular analyses have strongly supported the monophyly of Polygonaceae and its placement in the FTPP clade of Caryophyllales together with Plumbaginaceae, Tamaricaceae, and Frankeniaceae[7](https://phytokeys.pensoft.net/article/97667/download/pdf/). A genomic study estimated that the lineage diverged from its sister family approximately 65.59 million years ago, followed by major generic diversification within the family around 60.11 million years ago[8](https://doi.org/10.1016/j.celrep.2025.116558).
The first large-scale molecular phylogeny of the family was published in 2003, and inframilial relationships have been progressively resolved since; several genera, including Atraphaxis, Koenigia, Polygonum, and Ruprechtia, have been recircumscribed as a result, with some genera erected and others reduced to synonymy[7](https://phytokeys.pensoft.net/article/97667/download/pdf/). The Kew handbook recognizes two subfamilies, Polygonoideae and Eriogonoideae[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information), while chloroplast phylogenies recover Symmerioideae, represented by Symmeria paniculata, as the first-diverging lineage sister to a clade comprising Eriogonoideae and Polygonoideae[7](https://phytokeys.pensoft.net/article/97667/download/pdf/).
**Generic limits continue to be refined.** A 2023 study confirmed with chloroplast DNA data that the monotypic African genus Harpagocarpus is congeneric with [Fagopyrum](https://www.edgepedia.org/fagopyrum), placing H. snowdenii as sister to the woody buckwheat F. tibeticum, and proposed the first sectional classification of Fagopyrum into sect. Fagopyrum, sect. Tibeticum, and sect. Urophyllum[7](https://phytokeys.pensoft.net/article/97667/download/pdf/). Genome-scale work has also revealed extensive polyploidy: Fagopyrum-related Pleuropterus multiflora is diploid with 2n = 2x = 22, Calligonum mongolicum is tetraploid (2n = 4x = 34), and [Reynoutria japonica](https://www.edgepedia.org/reynoutria-japonica) is decaploid (2n = 10x = 100)[8](https://doi.org/10.1016/j.celrep.2025.116558).
## Distribution
The family is cosmopolitan but most diverse in northern temperate regions[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). In the western hemisphere, 31 genera occur, of which 16 are restricted to western North America, with 3 disjunct to Chile and Argentina[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). Coccoloba, Ruprechtia, and Triplaris are endemic to the Neotropics; Neomillspaughia, Podopterus, Gymnopodium, and Antigonon are restricted to [Central America](https://www.edgepedia.org/central-america); and the monotypic Leptogonum is endemic to [Hispaniola](https://www.edgepedia.org/hispaniola)[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). Polygonum, Rumex, and [Persicaria](https://www.edgepedia.org/persicaria) are cosmopolitan, and species of knotweed (Polygonum) are particularly invasive in Europe[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). In Mexico the family is represented by 173 species and ranks among the country's 50 richest plant families[9](https://www.scielo.org.mx/scielo.php?lng=es&nrm=iso&pid=S0187-71512026000100112&script=sci_arttext).
## Uses
Several species are food plants. Buckwheat (Fagopyrum esculentum) is grown for its seeds, which produce a flour; in Japan it is used to make soba pasta and is an increasingly popular gluten-free alternative to wheat[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). Rhubarb (Rheum) is grown for its edible petioles, and sorrel (Rumex) is eaten as a leaf vegetable; some species have medicinal uses and others are ornamentals[3](https://www.benthamscience.com/chapter/25539) • [2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). Antigonon leptopus, a Mexican native known as Corallita, is widely cultivated as an ornamental for its showy flowers[2](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information). In the Neotropics, the fleshy fruits of [Coccoloba](https://www.edgepedia.org/coccoloba) are edible and made into jelly[10](https://manoa.hawaii.edu/lifesciences/faculty/carr/polygon.htm).
## References
1. [Polygonaceae Juss., Plants of the World Online, Kew Science](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2)
2. [Polygonaceae Juss., general information (descriptions from Kew sources), Plants of the World Online, Kew Science](https://powo.science.kew.org/taxon/urn%3Alsid%3Aipni.org%3Anames%3A30000532-2/general-information)
3. [Wild Vegetables of the Family Polygonaceae, Bentham Science](https://www.benthamscience.com/chapter/25539)
4. [Polygonaceae, an overview, ScienceDirect Topics](https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/polygonaceae)
5. [Family Polygonaceae, Die Pflanzen der Hohenheimer Gärten, Universität Hohenheim](https://virtuelle-gaerten.uni-hohenheim.de/4DACTION/W_Init/HG_Family_en?HTID=HOH-3740)
6. [Family guide for fruits and seeds: Polygonaceae Juss., nom. cons., DELTA](https://www.delta-intkey.com/famfs/www/polygo.htm)
7. [Min, D. et al. (2023). The molecular phylogenetic position of Harpagocarpus (Polygonaceae) sheds new light on the infrageneric classification of Fagopyrum. PhytoKeys 220: 109–126](https://phytokeys.pensoft.net/article/97667/download/pdf/)
8. [Genomic insights into karyotype evolution and adaptive mechanisms in Polygonaceae species, Cell Reports (2025)](https://doi.org/10.1016/j.celrep.2025.116558)
9. [Conocimiento florístico de la familia Polygonaceae en México, Acta Botanica Mexicana](https://www.scielo.org.mx/scielo.php?lng=es&nrm=iso&pid=S0187-71512026000100112&script=sci_arttext)
10. [Flowering Plant Families, UH Botany: Polygonaceae](https://manoa.hawaii.edu/lifesciences/faculty/carr/polygon.htm)
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*Topic: Encyclopedia › Life and health › Plants and algae › Seed plants › Other flowering plants*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license