Imperata cylindrica (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Spice / condiment|
|Carbohydrate / starch|
|Forage / feed|
Imperata cylindrica (L.) Raeusch.
- Protologue: Nomencl. bot., ed. 3: 10 (1797).
- Family: Poaceae (Gramineae)
- Chromosome number: 2n = 20
- Imperata arundinacea Cirillo (1792).
- Speargrass, imperata, cogon grass, alang-alang, lalang, blade grass, blady grass, cottonwool grass, woolly grass, thatch grass, silver spike (En).
- Herbe à paillotte, paillotte, impérate, chiendent, paille de dys (Fr).
- Sapé, caminhadora, capin seno, imperata (Po).
- Unyasi (Sw).
Origin and geographic distribution
Speargrass is widely distributed throughout the tropics and subtropics of Africa, the Indian subcontinent, South-East Asia and Australia. It occurs to a lesser extent in North, Central and South America, and is also found in warm temperate areas, being recorded at latitudes of 45° in New Zealand and Japan. In Africa it occurs in almost all countries, including northern Africa and South Africa.
The leaves and older stems are widely used for thatching. In Nigeria the Igala people bind the grass in rolls and place the rolls on the roof as thatch. The leaves are woven into mats, bags and baskets. In southern Africa the stems and leaves are moistened and twisted into rope, which is considered to be very durable. The seed fluff is used as pillow stuffing and as a substitute for cotton wool in treating sores. Imperata cylindrica can be used for making paper, and paper has commercially been produced in Australia.
Young foliage is tender and browsed by cattle and goats, but older leaves become tough and unpalatable and develop razor-sharp edges. Young foliage is also cut as fodder. In Lesotho the rhizomes are eaten raw by herdsmen and in Kenya Kipsigi children chew them for their sweet flavour. Attempts have been made to ferment the rhizomes into a beer and to extract sugar and alcohol from them but without commercial success. Young inflorescences and shoots are cooked and eaten as a vegetable, as the taste is rather sweet. Salt is made from the ash of the aerial parts, and the dried rhizome can be powdered and used as sweetener. Dry plants are burnt as fuel.
Speargrass is used for mulching, for instance in coffee and banana plantations, and the fast-growing rhizomes make it suitable for erosion control and stabilizing slopes. However, it is considered one of the 10 worst weeds in the world.
Speargrass has a range of traditional medicinal uses throughout tropical Africa. A decoction of the rhizome is widely drunk as a diuretic, to purify the blood and to treat dysentery, colic, hypertension and venereal diseases. A rhizome maceration is taken to treat cough, and the pulped-up plant with shea butter (Vitellaria paradoxa C.F.Gaertn.) is used as an embrocation for coughs. A decoction of the aerial parts or leaves is drunk to treat fever and malaria and is also used as a wash to treat furuncles and aphthae. In Senegal Fula people drink a rhizome decoction to treat schistosomiasis. In DR Congo ash of burnt roots is rubbed into scarifications to treat chest pain with high fever. Roots are eaten as a galactagogue. Roasted and powdered roots in palm oil are taken as an aphrodisiac. In Uganda the root is chewed to treat snakebites. In Namibia a root decoction is taken to treat jaundice and digestive problems. In southern Africa a crushed root infusion is taken to treat hiccups and indigestion. In Madagascar a decoction of the dried plant is taken as a gargle for sore throat, neuralgia and intestinal worms. In Japan the stems are used in a patented antitumour preparation. Speargrass is also used in various countries in South and South-East Asia for a wide range of medical problems such as fever, nausea, dropsy, jaundice, asthma, haematuria, influenza, emphysema, internal bleeding, nose bleed, cough and kidney diseases. A decoction of the rhizome is commonly applied to purify the blood, as a diuretic and in the treatment of diarrhoea and dysentery.
In Namibia the ground stems are used as a cosmetic. The stems are also cut in short pieces and strung for decorative purposes. A red-leaved ornamental cultivar ‘Red Baron’ or ‘Japanese blood grass’ has been developed for garden use in temperate regions.
Production and international trade
Speargrass is used only locally and has no importance in international markets.
To give adequate protection from rain, the pitch of roofs to be thatched with speargrass has to be steep and the thatch about 20 cm thick, requiring a strong support. This type of thatch may last 2–3 years. Plant material from Nigeria (mainly leaves, with thin stems and some rhizome parts) investigated in the 1910s contained 46% cellulose on a dry matter basis. The fibre cells were (0.6–)0.8–1.1(–1.3) mm long. Leaf material from Sri Lanka (mainly leaf blades, with a small proportion leaf sheaths) investigated in the 1930s contained 46% cellulose on a dry matter basis. The fibre cells were (0.2–)0.5–1.5(–3.0) mm long and (4.7–)6–9(–15.5) μm wide.
Speargrass is considered a low quality forage. Nitrogen concentrations may only remain above 1% for some 6 weeks when it grows rapidly, but can remain above this level for up to 20 weeks with slower growth rates at higher latitudes and altitudes. Very young growth may have a digestibility of 70%, falling to below 40% after 150 days. Where there is opportunity for selective grazing, other species are usually preferred.
The rhizome contains the biphenyl ethers cylindol A and B, the phenolic compound imperanene, the sesquiterpenoid cylindrene, the lignans graminone A and B and several chromone derivatives. It also contains about 19% sugars (saccharose, dextrose, fructose, xylose) and various acids (including malic, citric, tartaric, chlorogenic, coumaric and oxalic acid). From the aerial parts serotonin and the triterpenoids arundoin, cylindrin, fernenol, isoarborinol and aimiarenol were isolated. Cylindol A has shown 5-lipooxygenase activity, which may be partly involved in the reputed anti-inflammatory activity of speargrass. Imperanene has shown inhibitory activity against rabbit platelet aggregation. Cylindrene and graminone B have shown inhibitory effects on rabbit aorta contraction. Several chromone derivatives showed significant neuroprotective activity against glutamate-induced neurotoxicity in rat cortical cell cultures.
An aqueous extract of stem and leaves has shown some antitumour activity against sarcoma 180 and adenocarcinoma 75 in mice. Rhizome extracts significantly inhibited urination in rats.
Besides the above pharmacological activities, antiviral, antihepatotoxic, antihypertensive, antihistamine and larvicidal activities are also reported, as well as an allelopathic effect on the germination and growth of other plant species.
Perennial herb up to 120(–300) cm tall; rhizome deeply buried, white, branched, fleshy and scaly; stems solitary or tufted, erect, unbranched, solid, with 1–4(–8) nodes, nodes glabrous to hairy. Leaves mostly basal; sheath with ciliate margin, lower sheaths broad and leathery, overlapping; ligule membraneous, up to c. 1 mm long; blade linear-lanceolate, 10–80(–180) cm × 0.5–2.5 cm, flat or rolled, erect, spreading or drooping, long-acuminate at the apex, long-hairy at the base, older leaves with hard, serrate, cutting margins and a stout whitish midvein. Inflorescence a terminal, spike-like panicle, cylindrical, 6–30 cm × c. 2 cm, branches ascending close to the main axis. Spikelets in pairs, 3–6 mm long, 2-flowered, at the base with a dense whorl of silky white hairs up to 2.5 cm long; pedicels unequal, up to 1 mm long; glumes equal, 3–9-veined; lower floret reduced to a hyaline lemma; upper floret bisexual, lemma ovate, c. 1 mm long, palea hyaline, lodicules absent, stamens 2, anthers orange to purple, stigmas 2, purple. Fruit an ellipsoid caryopsis (grain) c. 1 mm long, brown.
Other botanical information
Imperata comprises about 10 species and originates in the New World. It is divided into two sections, based on the number of stamens: section Imperata (2 stamens) with only 1 species (Imperata cylindrica), and section Eriopogon (1 stamen). A number of varieties have been described for Imperata cylindrica, often related to geographical regions. However, as these varieties more or less intergrade, the distinction is usually ignored.
Growth and development
The optimum temperature for growth of speargrass is about 30°C with negligible growth at 20°C and 40°C. The rhizomes are highly competitive and penetrate the roots of other plants, causing rot or death. In a controlled greenhouse experiment young plants initiated new rhizomes between the third and fourth leaf-stages. Rhizome growth is determinate, with the apical bud forming a shoot and sub-apical buds forming rhizome branches. Under favourable conditions, apical and sub-apical buds develop simultaneously, but under stress the growth of the apical bud is favoured. Roots and buds develop at the distal nodes of the young rhizome long after the rhizome has been formed. Flowering is variable between individual plants and stands, but generally occurs in spring or fall, and often in response to a range of disturbances (e.g. burning, mowing, soil disturbance) throughout the year. Frequent fires encourage the growth and uniformity of the population. Seedlings establish well after burning. Incapable of self-pollination, speargrass produces viable seed only when cross-pollinated and the success rate of outcrossing is low, less than 40% in natural populations. Still, speargrass may produce as many as 3000 seeds per plant. Seeds are dispersed by wind, up to 100 m away. Speargrass is a C4 plant.
Speargrass occurs from sea-level up to 2000(–2700) m altitude in a wide range of open, anthropogenic habitats, preferring well-aerated soils. It is often found in areas with an average annual rainfall over 1000 mm, but has been recorded in sites receiving from 500 to 5000 mm per year. It will grow in full sun as well as in light shade. Speargrass tolerates temperatures down to about –15°C when dormant, but young growth in spring in temperate climates can be damaged by late frosts. Speargrass generally occurs on light-textured acid soils with a clay subsoil, but can tolerate a wide range of soils from strongly acidic to slightly alkaline, with a pH of 4.0–7.5, although germination is promoted by a pH lower than 5. It grows most vigorously in wet soil of reasonable fertility, and can even tolerate very hot, sulphurous conditions in active volcanic areas. Speargrass can withstand waterlogging but not continuous flooding; it is salt-tolerant.
Speargrass is one of the most noxious colonizers of degraded humid tropical forest soils and often invades abandoned shifting cultivation fields. The tendency to form dense, persistent and expanding stands allows it to displace other vegetation. Its abundant biomass prevents establishment of other plants and changes the properties of the litter and upper soil layer.
Propagation and planting
Speargrass is propagated by seed or rhizomes. The seed has no dormancy and seeds may show 95% germination within one week after maturation. Seed germination in the dark increased from 9% at 20°C to 55% at 30°C and declined somewhat at 35°C. Germination was about 70% in the light with alternate 12-hour periods at 20°C and 30°C. Addition of 0.2% KNO3 solution increased germination in the dark, but not in the light. Germination declined gradually after 13 months of storage. Rhizomes are very resistant to heat and breakage, and may penetrate soil up to 1.2 m deep, but generally occur in the top 15 cm in heavy clay soils, and 40 cm of sandy soils. Rhizome biomass can reach 40 t/ha fresh weight and regrowth potential of roots is a critical issue in development of control methodologies, including biological control. Rhizomes accidentally cut by cultivation can re-establish from pieces as small as 5 mm. Success of segment regeneration is determined by the original location of the segment on the rhizome, including proximity to, or inclusion of, axillary and apical buds, as well as by environmental conditions. Vegetative reproduction from rhizomes is a significant factor in human spread of the species because these are often found in dirt moved as fill.
Speargrass is favoured by burning, which can lead to virtually monospecific populations, also called ‘swards’. If speargrass is to be used for thatching, populations are left ungrazed until after the mature growth has been cut. It has been suggested that speargrass that is used regularly for grazing should be grazed rotationally when 15–25 cm high. Because of its aggressiveness and low quality, it is widely regarded as a weed and research has been carried out on improving its quality through introducing legumes or even replacing it with other grasses. However, it is not easy to maintain herbaceous legumes with speargrass, though some promising results have been achieved with stylo (Stylosanthes guianensis (Aubl.) Sw.) and leucaena (Leucaena leucocephala (Lam.) de Wit).
Throughout the tropics, including natural grasslands, speargrass covers an area estimated at 5,000,000 km², of which 2,000,000 km² in South-East Asia. Speargrass can best be suppressed by an integrated management strategy, including different cover crops, heavy continuous grazing, frequent cutting, frequent cultivation and chemical and/or biological control, although these last 2 methods are generally considered to be too expensive.
Frequent cutting and frequent mechanical cultivation, however, may result in loss of fertility. Forking and removal of the rhizomes by hand is completely effective but this is only practical if infestation is light and sporadic and the area small.
Diseases and pests
There are no records of major diseases or pests for speargrass.
For thatching, the longer the grass the better, and the leafy stems should be cut after the seed has ripened but before the plant has dried out and become brittle. The cut plants must be combed to remove the soft leaves and short pieces and should then be dried, after which they are tied in bundles about 20 cm in diameter. For medicinal purposes, plants are simply uprooted to collect the rhizomes, or aerial parts are harvested whenever the need arises.
Reported above-ground dry matter yields of speargrass are 2–12 t/ha per year. In Indonesia a production has been recorded of 11 t/ha of leaves and 7 t/ha of rhizomes, with on average 4.5 million shoots.
Handling after harvest
Harvested plant parts are usually dried before being used as thatch, or used fresh as fodder or for medicinal purposes.
Speargrass is widespread and common, usually even considered a noxious weed. Its spread is favoured by human activities, and it is therefore certainly not threatened by genetic erosion.
The red-leaved ornamental cultivar ‘Red Baron’ or ‘Japanese blood grass’ has been reported to be able to revert to the green, invasive form, especially when the plant has been propagated by tissue culture.
Although speargrass is widely considered a serious weed, it can be useful for various purposes, especially to provide thatching material when mature and fodder when young. Its use to control erosion is valuable as well, but alternatives should be tested before using it. A broad range of medicinal uses has been reported, but most claims still need to be validated. Most research on speargrass is focused on finding the most efficient and cheap ways of eradicating it from farm land. As with most highly invasive weeds, an integrated management strategy seems the only viable way.
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Sources of illustration
- Aguilar, N.O., 1992. Imperata cylindrica (L.) Raeuschel. In: ’t Mannetje, L. & Jones, R.M. (Editors). Plant Resources of South-East Asia No 4. Forages. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 140–142.
- J.P. Lepetu, Faculty of Agriculture, Botswana College of Agriculture, Private Bag 0027, Gaborone, Botswana
Correct citation of this article
Lepetu, J.P., 2011. Imperata cylindrica (L.) Raeusch. [Internet] Record from PROTA4U. Brink, M. & Achigan-Dako, E.G. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 1 March 2020.
- See the Prota4U database.