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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.
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Taxonomy
This family is very well-defined and is universally recognised, but its position has been less clear. For example, in the Cronquist system, it was given its own order (Polygonales), but newer systems such as APG treat them as part of the Caryophyllales.
Polygonaceae can be divided in two subfamilies:
- Polygonoideae, comprising about 28 genera and 800 species, are characterised by the lack of an involucre and the presence of ocreae. Important members are Polygonum, Rumex and Calligonum.
- Eriogonoideae, with about 330 species, are exclusive to the New World and are characterised by the involucre, cymose inflorescence and lack of ocreae. Important members are Eriogonum and Coccoloba.
Description
Most Polygonaceae are perennial herbaceous plants with swollen nodes, but small shrubs (e.g. Coccoloba) and climbers (e.g. Antipogon) are also present.
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.[1]
Selected genera
- Afrobrunnichia
- Antigonon
- Antipogon
- Aristocapsa
- Atraphaxis
- Brunnichia
- Calligonum
- Centrostegia
- Chorizanthe
- Coccoloba
- Dedeckera
- Dodecahema
- Emex
- Eriogonum
- Fagopyrum
- Fallopia
- Gilmania
- Goodmania
- Gymnopodium
- Harfordia
- Hollisteria
- Knorringia
- Koenigia
- Lastarriaea
- Leptogonum
- Mucronea
- Muehlenbeckia
- Nemacaulis
- Neomillspaughia
- Oxygonum
- Oxyria
- Oxytheca
- Parapteropyrum
- Persicaria
- Podopterus
- Polygonella
- Polygonum or Knotweed
- Pteropyrum
- Pterostegia
- Rheum
- Rumex
- Ruprechtia
- Stenogonum
- Symmeria
- Systenotheca
- Triplaris
External links
- Polygonaceae in L. Watson and M.J. Dallwitz (1992 onwards). The families of flowering plants: descriptions, illustrations, identification, information retrieval. http://delta-intkey.com
References
- ^ Jones, Samuel B., and Arlene E. Luchsinger. 1979. Plant systematics. McGraw-Hill series in organismic biology. New York: McGraw-Hill. Page 254. ISBN 0-07032795-5
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