The nut-grass (Cyperus rotundus) is a slender, erect, perennial sedge which spreads by means of a fibrous root system (2) (3) (4) (5) (6). Its slender, underground stems, known as rhizomes, are initially white, fleshy and covered with scaly, modified leaves, but become brown and woody with age. On reaching the surface, a rhizome may swell into a small, rounded structure called a ‘basal bulb’, from which shoots, roots and further rhizomes arise (4) (5). The rhizomes of the nut-grass also form tubers, which store starch as a food reserve and can give rise new rhizomes or new plants. The tubers measure around 1 to 3.5 centimetres in length and are white and succulent when young, later turning brown and hard (2) (3) (4) (5) (6). The shape of the tubers gives the nut-grass its scientific name, ‘rotundus’, meaning ‘round’ (2).
The stems of the nut-grass are smooth and erect, usually reaching around 30 to 40 centimetres in height, and are triangular in cross-section (2) (3) (4) (6). The leaves originate from the base of the plant and are arranged on the stem in groups of three (2) (4) (5). They are smooth, shiny and dark green, with a grooved upper surface and a sharp tip (2) (4) (5), and are long and narrow, generally measuring up to 20 to 30 centimetres in length and 0.2 to 1 centimetres in width (3) (4) (5) (6).
The flowers of this species are borne in clusters (inflorescences) at the ends of the stems. The inflorescence consists of around three to nine stalks of varying lengths, at the ends of which are reddish-brown to purple ‘spikelets’ (2) (3) (4) (5) (6). The colour of the spikelets gives the nut-grass its alternative name of ‘purple nutsedge’. Each spikelet measures up to 3.5 centimetres in length (2) and consists of 10 to 40 flowers (4) (5) (6), which lack petals (4), but instead sit within dry, membranous, oval-shaped bracts, known as ‘glumes’ (2) (5) (6). The nut-grass produces a dry, single-seeded fruit, which is up to two millimetres long, and brown to black with a network of grey lines (2) (3) (4) (5) (6).
Four subspecies of the nut-grass have been identified: Cyperus rotundus rotundus, Cyperus rotundus divaricatus, Cyperus rotundus merkeri and Cyperus rotundus retzii (1). This species is sometimes found growing together with the closely related yellow nutsedge (Cyperus esculentus), but is most easily distinguished from its relative by its purplish rather than yellow inflorescences (5).
- Also known as
- coco sedge, cocograss, coco-grass, nutgrass, nutsedge, purple nut sedge, purple nutsedge, purple nut-sedge, red nut sedge.
- Chlorocyperus odoratus, Chlorocyperus rotundus, Chlorocyperus tetrastachyos, Chlorocyperus tuberosus, Cyperus merkeri, Cyperus nubicus, Cyperus retzii, Cyperus taylorii, Schoenus tuberosus.
- Souchet Rond.
- Height: up to 100 cm (2)
Together with its ability to tolerate a wide range of soils and environmental conditions, the underground tuber system of the nut-grass makes it a highly successful plant species. Its tubers are able to remain dormant and survive extreme conditions, and also allow the nut-grass to spread rapidly through the production of many new tubers, basal bulbs and rhizomes (2) (4).
The flowers of the nut-grass are hermaphroditic, containing both male and female parts. Flowering may take place year-round in the tropics (4), and the period from the first emergence of the plant to its flowering takes around three to eight weeks (5). Unusually, seed formation does not appear to be an important form of reproduction in the nut-grass, and seed production and germination is low, with many plants not producing seed at all (2) (4) (5). Any seeds that are produced are able to remain dormant in the soil for up to eight years (4).
A common and widespread species, the nut-grass is found throughout tropical and subtropical regions around the world. It is thought to be native to Asia (4), but has been introduced and become established in many countries outside of its natural range (1) (2) (4).
The extensive distribution of the nut-grass is due to its ability to adapt to a wide range of soil types, altitudes, temperatures, soil pH and moisture levels (2) (4). It therefore grows in a variety of different habitats and environments (1) (6), although in cooler and wetter areas it may grow more slowly and produce fewer flowers and tubers (6).
The nut-grass is tolerant of habitat disturbance and often grows in waste places or amongst crops, in lawns or on roadsides, It also commonly occurs in wet grasslands, swamps and bushland (1) (6).
The nut-grass is classified as Least Concern (LC) on the IUCN Red List (1).
The nut-grass is an abundant and widespread plant and is not facing any major threats (1). This species is highly tolerant of habitat disturbance (1), and has been described as the “world’s worst weed” due to the damage it causes to agriculture around the world (3) (4). The nut-grass spreads rapidly, is difficult to control and is often able to outcompete crops (3) (4), and it is also a serious pest in gardens, industrial sites and nurseries (6).
As well as being adaptable and spreading easily, the nut-grass produces substances in its tubers and other underground parts which inhibit the growth of other plants (2) (4). However, these substances are believed to have many medicinal properties, and have been used to treat stomach disorders, diarrhoea, headaches and malaria, as well as being used as anti-inflammatories and for healing wounds (5) (6) (7) (8) (9). Extracts from the tubers are also used to pigment hair and skin (9). Although distasteful (5), the tubers have been eaten as food during famines, and the nut-grass has also been used as animal feed (6).
This successful plant occurs in many protected areas across its large range (1), and does not require any specific conservation measures. Most of the management of the nut-grass focuses on its control as a damaging weed (2) (4) (6).
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- Modified leaf at the base of a flower.
- Possessing both male and female sex organs.
- The reproductive shoot of a plant, which bears a group or cluster of flowers.
- A plant that normally lives for more than two seasons. After an initial period, the plant produces flowers once a year.
- An underground, horizontal plant stem that produces roots and shoots.
- A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- In plants, a thickened stem or root that acts as an underground storage organ. Roots and shoots grow from growth buds, called ‘eyes’, on the surface of the tuber.
IUCN Red List (March, 2011)
Hall, D.W., Vandiver, V.V. and Ferrell, J.A. (2009) Purple Nutsedge, Cyperus rotundus L.. Institute of Food and Agricultural Sciences, University of Florida. Available at:
Flora of North America - Cyperus rotundus (March, 2011)
Centro Internacional de Agricultura Tropical (1984) The Biology and Control of Purple Nutsedge (Cyperus rotundus L.). Centro Internacional de Agricultura Tropical, Cali, Colombia.
Wills, G.D. (1987) Description of purple and yellow nutsedge (Cyperus rotundus and C. esculentus). Weed Technology, 1: 2-9.
Galinato, M.I., Moody, K. and Piggin, C.M. (1999) Upland Rice Weeds of South and Southeast Asia. International Rice Research Institute, Makati City, Philippines.
Puratchikody, A., Devi, C.N. and Nagalakshmi, G. (2006) Wound healing activity of Cyperus rotundus linn. Indian Journal of Pharmaceutical Sciences, 68(1): 97-101.
Uddin, S.J., Mondal, K., Shilpi, J.A. and Rahman, M.T. (2006) Antidiarrhoeal activity of Cyperus rotundus. Fitoterapia, 77: 134-136.
Khare, C.P. (2007) Indian Medicinal Plants: An Illustrated Dictionary. Springer-Verlag, Berlin.