Nutgrass

Cyperus rotundus L.

Synonyms - Cyperus odoratus, Cyperus tuberosus.

Family: Cyperaceae.

Names:

Cyperus is from the Greek kypeiros or the Latin cuperos both meaning sedge or rush.
Rotundus is Latin for round and refers to the round tubers on the roots.
Nutgrass refers to the nut like tubers on the roots and the grass like leaves.

Other names:

Coco Grass
Dila
Motha (India)
Nut Sedge
Purple Nut Grass (California)
Purple Nutsedge (USA)
Red Grass (South Africa)
Red Nutgrass (South Africa)
Teki (Indonesia)
Wintjiekweed (South Africa)
Water Grass

Summary:

A sedge with brown seed heads subtended by 3-4 leaves at the top of a triangular stem with basal leaves and a creeping wiry rhizome with underground oval tubers or "nuts".

Description:

Cotyledons:

One.

First leaves:

Leaves:

Long slender grass like leaves at ground level. Usually about 10, emerging in 3 rows at ground level. Shorter than the stem. Tough and fibrous.
Blade - Dark to bright green, shiny, smooth, coarse, tough and fibrous, slightly serrated, narrow, 50-200 mm long x 3-6 mm wide, taper to a fine point. Hairless. Prominent vein on the underside.
Ligule - None.
Sheath - Conspicuous loose sheath, sometime fibrous, reddish brown on lower leaves.
Long slender bracts (usually 3) at the top of the stem below the flowers.

Stems:

Erect, stiff, slender, triangular from top to bottom, ribbed. Up to 750 mm tall, usually 150-300 mm tall x 1.5-3 mm wide, thickened at the base, no joints, unbranched. Stems usually longer than leaves. Wiry rhizomes.

Flower head:

Simple, loose umbel of 3-8 slender rigid primary rays of differing lengths, held at an oblique angle(rarely has secondary rays), up to 150 mm long x 100 mm wide overall, usually 40-80 mm long and wide. Borne singly in dense clusters above 2-4 bracts at the top of stems. 3-10 brown spikelets per egg shaped spike or cluster which is 10-20 mm long x 2-2.5 mm wide and remains on the plant for a long time. Backbone (rachilla) prominently winged, persistent.

Flowers:

Bracts - 2-6, up to 300 mm long. Lower one about as long or longer than the flower head.
Spikelets - Brown to purple, flattened and narrow, unequal lengths, 10-40 mm long x 1-2 mm wide, with 10-40 closely packed florets and seeds. Reddish/purple to brown. Stalkless. Emerge from an almost common point.
Florets - 3 branched style. Bisexual flowers present. Style 3 branched, not dilated at the base.
Glumes - In 2 rows, 3-4 mm long, green keeled, 5-7 nerves, flattened not pointed, sides purplish brown.
Perianth - None
Stamens - 3.
Anthers - 2 mm long.

Fruit:

Black, brown grey or olive green, small, triangular pyramidal nut, about 1-1.5 mm long or half the length of the glume.
In some subspecies it often does not mature.

Seeds:

Common subspecies rarely produce viable seed.

Roots:

Fibrous roots, rhizomes, tubers and basal bulbs.
Wiry, thin, long, more or less horizontal, fibrous creeping rhizomes with strings of up to 15, white to purplish, hard swollen elliptical tubers(nuts), up to 25 mm long and usually around 12 mm long. Tubers may be naked or have a fibrous coat of scales and are up to 10 mm wide. Scales are egg to spear shaped, pale and with an acute tip. Roots fragrant and bitter to taste. Deep and extensive. Fibrous roots produced from tubers and plant bases. Tubers are succulent, white turning reddish to blackish with age, have 6-10 buds which can produce new plants. Basal bulbs form at he base of the stem just below ground level.
Dense mats of tubers and rhizomes may form in the top 150 mm of soil with roots extending to a metre deep.

Key Characters:

Long wiry rhizomes with elliptical tubers or nuts. Spikelets arrange in groups of less than 10.

Biology:

Life cycle:

Perennial.
In southern Australia seeds germinate in spring and the plant grows over summer forming rhizomes and tubers and flowers in autumn to winter. Tubers shoot in spring and extend to the surface to produce a basal bulb that produces the leaves. These grow over summer producing more tubers and rhizomes and flower in autumn to winter. Under good conditions plants may flower when they are 3-6 weeks old.

Physiology:

Grows poorly in shaded areas but quickly recover if shade is removed.
Sensitive to salinity.
Grows poorly at low temperatures of less than 20 degrees C.
Tubers are rich in starch.
C4 plant.

Reproduction:

By seed and tubers.

Flowering times:

April to August in SA.
April to July in Perth.

Seed Biology and Germination:

Seed production is variable and viability is often low (see Hybrids).

Vegetative Propagules:

Tubers give rise to new shoots and rhizomes. Sprouting of tubers is low when temperatures are less than 20 degrees C. Sprouting of one tuber inhibits the sprouting of adjacent tubers attached by the rhizome. Disturbance that breaks this connection results in most tubers sprouting. Tuber dormancy is high on undisturbed sites and they may survive in the soil for at least 7 years. Tuber dormancy increases with depth. Shoots from tubers will push through bitumen and plastic. They can establish when covered with up to a metre of soil.

Hybrids:

Several sub species:
Ssp. rotundus - stems 150-300 mm tall, tuber scales not present in the second year, spikelets 2 mm wide, glumes 3-3.5 mm long and obliquely erect, nut usually doesn't mature. This subspecies is probably an introduced plant.
Ssp. retzii - stems 500-750 mm high, tuber scales usually persist into the second year, spikelets about 2.5 mm wide, glumes 3.5-4 mm long and soon spread and roll inwards, nut matures.

Allelopathy:

Root exudates and leachate from dry material affect the growth of some companion plants and crops.

Population Dynamics and Dispersal:

Spread by seeds or vegetatively by tubers. It usually produces little seed, which germinates poorly, and few seedlings survive under field conditions. Tubers are responsible for most of the spread. Cultivation equipment and flood waters and to a lesser extent mud assist spread at a local level. Movement of contaminated soil in pot plants, on machinery and as fill account for most of the long distance spread.
One tuber can produce 600 plants and spread 3 m in a year, however spread by extension of rhizomes is usually less than 1 metre per year. Up to 53,000 tubers have been counted in a cubic metre of soil. 4 t ha-1 of tuber, rhizome and root can be produced in a year.

Origin and History:

Cosmopolitan. Native to the Pilbara and Kimberly and probably India also. Found in most tropical and sub tropical countries.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Prefers moist soils and irrigated land.

Climate:

Tropical and subtropical. Temperate.

Soil:

Prefers moist soils and depressions of moderate to high fertility.

Plant Associations:

Significance:

One of the worlds worst weeds. A serious weed in 52 crops in more than 90 countries.

Beneficial:

Grazed to a limited extent by horses and cattle but of little forage value.
Fragrant roots used in perfumes.
Tubers are edible and were a source of food for aboriginals.
Used to bind soil to prevent wind erosion.
Used in Chinese and Indian herbal medicine as a diuretic, anthelmintic and for the treatment of coughs, fever and bronchial asthma.

Detrimental:

Listed as one of the worlds worst weeds.
A serious weed of horticulture, floriculture, orchards, vineyards, gardens, parks and disturbed areas.
Weed of cultivated crops, rotation crops, perennial crops, grass land pasture, cotton, maize, sugar cane and tobacco.
Interferes with cultivation especially in vineyards and orchards.
Acts as a host for nematodes and insects of agriculture.

Toxicity:

Not recorded as toxic.

Legislation:

Noxious weed of Victoria.

Management and Control:

Cultivation during the winter dormant period encourages nuts to sprout so herbicides can be used more effectively. Cultivation each fortnight for a year provides some control. Cultivation to a depth of 300 mm followed by workings to 150 mm deep with tined implements when the soil is dry is most effective. Small areas are often fumigated. Glyphosate, amitrole, hormone and urea herbicides have action on this weed. Glyphosate applied at the flowering stage has generally given the best control. It usually requires repeated treatments.
Flooding for several weeks is used overseas.
Pigs and geese root out the tubers but provide only partial control of the weed.

Thresholds:

Colonies of over 500 plants m-2 can form which smothers most companion species.

Eradication strategies:

Eradication concentrates on depleting the perennial tubers.

Herbicide resistance:

Biological Control:

Many biological control programs have been implemented without a great deal of success.

Related plants:

There are 38 Cyperus species recognised as economic plants by CSIRO the most common are:
Boredrain Sedge (C. laevigatus)
Clubrush (C. hamulosus)
Dirty Dora (C. difformis)
Dense Flatsedge (C. congestus)
Downs Nutgrass (C. bifax)
Dwarf Sedge (C. pygmaeus)
Dwarf White Kyllingia (C. kyllingia)
Flat Sedge (C. sanguinolentus)
Giant Sedge (C. exaltatus)
Kyllinga weed (C. sesquiflorus, C. sphaeroideus)
Mullumbimby Couch (C. brevifolius)
Nalgoo (C. bulbosus)
Navua sedge (C. aromaticus)
Nutgrass (C. rotundus)
Rice Flatsedge (C. iria)
Scaly Sedge (C. tenuiflorus)
Slender Sedge (C. gracilis)
Sticky Sedge (C. fulvus)
Stiff-leaved Sedge (C. vaginatus)
Spiny Flatsedge (C. gymnocaulos)
Tiny Flatsedge (C. tenellus)
Umbrella grass (C. eragrostis)
Yelka (C. victoriensis)
Yellow Nutgrass (C. esculentus)

Plants of similar appearance:

Kyllinga weed (C. sesquiflorus) has a very short or no rhizome. The spikes are whitish or pale green and it often has 2 small spikes at the base of a larger one.
Kyllinga weed (C. sphaeroideus) has a yellowish seed head, usually less than 50 flowers and is an annual.
Yellow Nutgrass (C. esculentus) is very similar until flowering when it produces a yellow green flower head.
Downs Nutgrass (C. bifax) has smaller tubers.
Grasses, sedges, some lilies.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P24. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P266. Diagram.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P78.

Ciba Geigy (1982) Grass Weeds 3. CIBA GEIGY Ltd, Basle, Switzerland. P24. Diagrams.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #404.29.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P880.

Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). p42-45. Diagram. Photos.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P57-61. Photos

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.