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Polygonum plebeium R.Br.

Protologue
Prodr.: 420 (1810).
Family
Polygonaceae
Chromosome number
2n = 20
Synonyms
Polygonum herniarioides Delile (1813), Polygonum roxburghii Meisn. (1856).
Vernacular names
Small knotweed (En).
Origin and geographic distribution
Polygonum plebeium is widespread all over tropical Africa, Asia and Australia. In some regions it is rare (e.g. DR Congo).
Uses
Polygonum plebeium is eaten as a vegetable in Malawi, cooked with potatoes and groundnuts. The product is slimy but well liked because it has a good smell. In India it is used as a famine vegetable, and it is grazed by horses. In Australia crushed seeds are cooked and eaten against bowel complaints; in India the roots are similarly applied.
Properties
Dry Polygonum plebeium leaves contain per 100 g dry matter: protein 17 g, fat 3 g, carbohydrate 50 g, fibre 16 g, P 0.3 g (Hooper, D., 1904). When grown in dry places the leaves are said to be bitter. The fresh root contains 11% tannin, and oxymethylanthraquinone has also been isolated.
Botany
Prostrate annual herb, much-branched, glabrous; stems up to 35 cm long, scabrid, red -brown, with short internodes. Leaves alternate, simple; ocrea cylindrical, up to 3 mm long, often silvery-white, irregularly fringed; petiole very short; blade very small, linear to obovate -elliptical, 1–2 cm × 2–5 mm, margin revolute, rather thick and leathery, dark green turning red. Inflorescence a congested raceme with short branches, forming axillary, 1–5-flowered clusters. Flowers bisexual; perianth 2 mm long, greenish, with 4 lanceolate-elliptical lobes 1.5 mm long, the outer pair keeled, white to pale pink; stamens 5–8; ovary superior, 1-celled, styles 3, free, 3 mm long. Fruit a trigonous nut up to 2 mm long, smooth, shiny black.
Ecology
Polygonum plebeium occurs in drier locations than many other Polygonum species, such as rocky ground in dried riverbeds and drying mudflats along lakes, in eastern Africa usually at 600–2400 m altitude. It also grows as a weed in fields.
Management
Polygonum plebeium is collected from the wild and is not cultivated.
Genetic resources and breeding
Polygonum plebeium is very widespread and is not in danger of genetic erosion.
Prospects
Polygonum plebeium will remain a locally important vegetable, particularly in times of scarcity. Its nutritive and medicinal properties need more research.
Major references
• Burkill, H.M., 1997. The useful plants of West Tropical Africa. 2nd Edition. Volume 4, Families M–R. Royal Botanic Gardens, Kew, United Kingdom. 969 pp.
• Graham, R.A., 1958. Polygonaceae. In: Turrill, W.B. & Milne-Redhead, E. (Editors). Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 40 pp.
• Williamson, J., 1955. Useful plants of Nyasaland. The Government Printer, Zomba, Nyasaland. 168 pp. (Reprint: Williamson, J., 1975. Useful plants of Malawi. University of Malawi, Zomba, Malawi).
Other references
• Hedberg, O., 2000. Polygonaceae. In: Edwards, S., Mesfin Tadesse, Demissew Sebsebe & Hedberg, I. (Editors). Flora of Ethiopia and Eritrea. Volume 2, part 1. Magnoliaceae to Flacourtiaceae. The National Herbarium, Addis Ababa University, Addis Ababa, Ethiopia and Department of Systematic Botany, Uppsala University, Uppsala, Sweden. pp. 336–347.
• Hooper, D., 1904. Analyses of Indian pot-herbs of the natural orders Amarantaceae, Chenopodiaceae, and Polygonaceae. Agricultural Ledger (Calcutta) 6: 423–434.
• Keay, R.W.J., 1954. Polygonaceae. In: Keay, R.W.J. (Editor). Flora of West Tropical Africa. Volume 1, part 1. 2nd Edition. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. pp. 137–142.
• Robyns, W., 1948. Polygonaceae. In: Robyns, W., Staner, P., De Wildeman, E., Germain, R., Gilbert, G., Hauman, L., Homès, M., Lebrun, J., Louis, J., Vanden Abeele, M. & Boutique, R. (Editors). Flore du Congo belge et du Ruanda-Urundi. Spermatophytes. Volume 1. Institut National pour l’Étude Agronomique du Congo belge, Brussels, Belgium. pp. 396–427.
Author(s)
P.C.M. Jansen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands


Editors
G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
O.A. Denton
National Horticultural Research Institute, P.M.B. 5432, Idi-Ishin, Ibadan, Nigeria
Associate Editors
C.-M. Messiaen
Bat. B 3, Résidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
R.R. Schippers
De Boeier 7, 3742 GD Baarn, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Jansen, P.C.M., 2004. Polygonum plebeium R.Br. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.