Polygonum nepalense (Nepal persicaria)
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IdentityTop of page
Preferred Scientific Name
- Polygonum nepalense Meisner (1826)
Preferred Common Name
- Nepal persicaria
Other Scientific Names
- Persicaria nepalensis (Meisner) H. Gross
- Polygonum alatum Sprengel (1827)
- Polygonum lyratum Nakai
- Polygonum punctatum var. alatum Buch.-Ham. ex D.Don (1825)
- Polygonum quadrifidum Hayata
International Common Names
- English: snake weed (India)
Local Common Names
- Bhutan: berkhey ratnaulo; helepsi; metoshim; shido
- Ethiopia: labuche
- Germany: Nepalesischer Koeterich
- Indonesia: asem tembagan; ganrot; hahaseuman; jukut asam
- Japan: tanisoba
- Sri Lanka: kangany-machan-pillu
- POLAL (Polygonum alatum)
- POLNE (Polygonum nepalense)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Polygonales
- Family: Polygonaceae
- Genus: Polygonum
- Species: Polygonum nepalense
Notes on Taxonomy and NomenclatureTop of page Hutchinson et al. (1954) give P. punctatum var. alatum as a synonym (together with P. alatum), while the P. punctatum Buch.-Ham. in southern India, illustrated by Tadulingam et al. (1955), is apparently the same species. P. punctatum Ell. , however, is a quite distinct temperate species (Hafliger and Wolf, 1988). Many Polygonum species, including P. nepalense and P. lapathifolium have recently been re-named as Persicaria species. Hence some modern floras, including Flora of Bhutan (Grierson and Long, 1983), use the name Persicaria nepalensis (Meisner) H. Gross. However, the more familiar older name is retained for the purposes of this Compendium.
DescriptionTop of page P. nepalense is an annual plant, prostrate to sub-erect, stems simple or branched 15-30(-45) cm high. Leaves are alternate, ovate to elliptic, up to 5 cm long, often with a pair of dark blotches each side of the mid-rib. The lamina is characteristically decurrent, causing the petiole to be effectively winged, and usually auriculate at the base. Foliage is generally glabrous, but punctate with scattered yellow glands on the underside. Ochreae are truncate, 6-10 mm long, sparsely pubescent. The individual flowers, 2-3 mm long, are usually pink, but sometimes white, with four perianth segments. They are carried in dense round clusters up to 1 cm in diameter, sessile or on peduncles up to 5 cm long , singly, or several subtended in upper leaf axils. Seeds are about 2 mm long, trigonous or biconvex, strongly pitted, black.
This description is based largely on Grierson and Long (1983). Everaarts (1981) has especially good drawings.
DistributionTop of page P. nepalense is believed to have originated in the Himalayas but it is now quite widespread, across the Asian, African and American continents and in the Pacific, but is apparently limited, as a significant weed, to high altitude tropics. Why it does not occur more commonly in temperate lowlands, which have roughly comparable temperature regimes is not clear. It can persist sporadically, in temperate regions, even as far north as the UK but is not reported as a weed problem.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
HabitatTop of page P. nepalense has seemingly strict environmental requirements, being largely restricted to the high altitude tropics, from 750-3000 m in Bhutan (Grierson and Long, 1983); 1200-2500 m in southern India (Tadulingam et al., 1955); 1400-2900 m in Ethiopia (Stroud and Parker, 1989) and 1500-2500 m in East Africa (Ivens, 1968). It might be expected to occur also at lower altitudes in temperate areas, but this is rarely so. Where it is common it occurs in a range of disturbed situations, mainly as a weed of annual and perennial crops, around field edges, in the open or in partial shade, usually in moist conditions.
Hosts/Species AffectedTop of page P. nepalense appears to have particular climatic requirements, being very much restricted to high altitude tropics, but within this ecology, it occurs in many, if not most of the crops grown. It is especially abundant in tea, both in India and in East Africa, perhaps encouraged by the repeated use of minimal doses of paraquat which do not provide complete control. It can, however, be predominant in other crops in the absence of any herbicide use. Everaarts (1981) notes that it is one of the commonest weeds of vegetables in highland Java, Indonesia.
Biology and EcologyTop of page P. nepalense is a relatively short-lived annual, completing development within 4-5 months, though this short period is perhaps partly due to attack by Puccinia polygoni-amphibii (Eden and Bond, 1925). Reproduction is solely by seeds which are produced in great abundance. Eden and Bond (1925) recorded over 30 million seeds/ha, often resulting in complete dominance under suitable conditions in, for example, the highlands of Sri Lanka, southern India and the Himalayas. The reason for its virtual restriction to these highland situations is unexplained. There are no reports of studies on germination behaviour, other than one from Japan indicating 50% viability maintained after 4.5 years storage in soil at 15 cm depth (Watanabe, 1978).
Eden and Bond (1925) indicate that P. nepalense is 'not particularly tolerant of shade' but its predominance in tea must suggest that it has some shade tolerance. The same authors studied the balance between P. nepalense and other weeds under different fertilizer regimes and showed that this species has a lower optimum phosphate level, and that addition of high phosphorus levels encouraged other weeds more and reduced the dominance of P. nepalense.
Everaarts (1981) indicates that P. nepalense prefers not too dry soils in open or lightly shaded situations and is favoured by high soil fertility.
Natural enemiesTop of page
ImpactTop of page P. nepalense is a weed which apparently only thrives in high altitude tropics but in these areas can become dominant. It is listed by Holm et al. (1979) as a 'principal' or 'serious' weed in Ethiopia, Sri Lanka and India. It is noted as being one of the six most prominent weeds of potato in the Nilgiri Hills of southern India (Nimje, 1988), one of the most important weeds of maize and potato in the 'dry subtropical' and warm and cool temperate zones between 1200 and 2400 m in Bhutan (Parker, 1992) and one of the three most aggressive weeds of wheat in Ethiopia (Gebre et al., 1987). Comparably, in Colombia, it was one of the predominant weeds of carrot on the altiplano de Pasto (Mena et al., 1984). In Indonesia, Everaarts (1981) refers to it as 'one of the commonest and troublesome weeds' of vegetables in highland Java at 1100-2300 m.
There are no reports on the competitive effect of P. nepalense and it has sometimes been regarded as relatively non-competitive in tea, to the point that it may be encouraged as a ground cover to suppress other, more serious, weeds (see Uses), but there can be little doubt that the dense infestations that can occur under suitable conditions must be competing significantly for nutrients.
UsesTop of page In Sri Lanka, P. nepalense has been regarded as a valuable ground cover, protecting soil from erosion (Eden and Bond, 1925). Weeding methods were deliberately aimed at encouraging P. nepalense in preference to other more troublesome species. It is not known whether this is still practiced, though in 1951, Haigh commented that P. nepalense was 'a very good cover for tea above 1000 m', only needing to be removed from around the base of bushes.
Similarities to Other Species/ConditionsTop of page Although there are many related Persicaria and Polygonum species occurring as weeds, none are likely to be confused with P. nepalense, due to the latter's distinctive leaf shape. The one exception in Bhutan and perhaps elsewhere in the Himalayas is P. runcinata [ Polygonum runcinatum] which has a similar inflorescence, and sometimes has a somewhat similar leaf shape, but is perennial, with leaves that are normally 'runcinate' with distinct lobes.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
P. nepalense is shallow-rooted and readily removed by manual or hoe weeding.
Recent information on the response of P. nepalense to herbicides is sparse. Older reports from Ethiopia show that it is susceptible to many of the standard herbicides for control of broad-leaved weeds, including MCPA, 2,4-D, dicamba, ioxynil, bromoxynil, fluorodifen, ametryne and prometryne (CADU, 1975; Anon., 1978). It is susceptible to terbutryne and methabenzthiazuron post-emergence, but possibly not pre-emergence. It was not controlled by bentazon. It is controlled by full doses of paraquat but may be relatively favoured by the use of reduced doses.
ReferencesTop of page
Eden T; Bond TET, 1925. The effect of manurial treatments on the growth of weeds in tea. Empire Journal of Experimental Agriculture, 13:141-157.
Ethiopia; Arssi Rural Development Unit; Crop and Pasture Section, 1978. Report on crop protection surveys and experiments 1976/77. Report on crop protection surveys and experiments 1976/77. P.O. Box 3376, Addis Ababa. Ethiopia, 75 pp.
Ethiopia; Chilalo Agricultural Development Unit, 1975. Crop protection activities, 1974. Parts from report on surveys and experiments carried out in 1974 by Crop and Pasture Section. Crop protection activities, 1974. Parts from report on surveys and experiments carried out in 1974 by Crop and Pasture Section. CADU. Asella Ethiopia, CADU Publication No. 111:147-195
Gebre H; Tarekegne A; Asmare E, 1987. Preliminary indications on the importance of yield limiting factors on wheat. Fifth Regional Wheat Workshop for Eastern, Central and Southern Africa and the Indian Ocean. Mexico City, Mexico: CIMMYT, 189-193
Grierson AJC; Long DG, 1983. Flora of Bhutan, Volume 1, Part 1. Edinburgh, UK: Royal Botanic Garden.
Hafliger TJ; Wolf M, 1988. Dicot Weeds. 1. Basle, Switzerland: CIBA-GEIGY Ltd.
Haigh JC, 1951. A Manual of the Weeds of the Major Crops of Ceylon. Peradenya Manual No. 7. Colombo, Sri Lanka: Department of Agriculture.
Hutchinson J; Dalziel JM; Keay RWJ, 1954. Flora of West Tropical Africa. Volume 1, Part 1, 2nd edition. London, UK: Crown Agents.
Ivens GW, 1967. East African Weeds and their Control. Nairobi, Kenya: Oxford University Press.
Mena F; Madronero E; Salcedo-Z A; Criollo-E H, 1984. A study of the critical period of competition between weeds and carrot (Daucus carota L.) crops on the Pasto plateau, Narino Department. Revista de Ciencias Agricolas, 8(1/14):114-120
Stace C, 1991. New Flora of the British Isles. Cambridge, UK: Cambridge University Press.
Tadulingam C; Venkatanarayana G; Mudaliar CR; Sakharam Rao J, 1955. A Handbook of some South Indian Weeds. Second edition. Madras, India: Madras Government Press.
Vibrans H; Hanan Alipi AM, 2008. Notes on neophytes 4. Polygonum nepalense (Polygonaceae), an invasive plant new for Mexico. (Notas sobre neófitas. 4. Polygonum nepalense (Polygonaceae), una planta invasora nueva para México.) Acta Botanica Mexicana, No.82:1-6. http://www.ecologia.edu.mx/publicaciones/ABM.htm
Wang ZR, 1990. Farmland Weeds in China. Beijing, China: Agricultural Publishing House.
Webb DA; Chater AO; Akeroyd JR, 1993. Polygonum L. In: Tutin TG, Burges NA , Chater AO, Edmondson JR, Heywood VH, Moore DM, Valentine DH, Walters SM, Webb DA, eds. Flora Europaea Volume 1 Psilotaceae to Platanaceae 2nd edition. Cambridge, UK: Cambridge University Press, 91-97.
Wells MJ; Balsinhas AA; Joffe H; Engelbrecht VM; Harding G; Stirton CH, 1986. A catalogue of problem plants in South Africa. Memoirs of the botanical survey of South Africa No 53. Pretoria, South Africa: Botanical Research Institute.
Distribution MapsTop of page
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