Mossman River grass

Cenchrus echinatus L.

Synonyms - Cenchrus brevisetus, Cenchrus pungens, Cenchrus quinquevalvis, Cenchrus viridis.

Family: Poaceae.

Names:

Cenchrus is from the Greek word kenchros for Millet.
Echinatus is from the Greek word ekhinos for hedgehog or sea urchin and refers to the spiny burrs.
Mossman River grass refers to the area in northern Queensland where it grows.

Other Names:

Arroz bravo (Brazil)
Burrgrass
Burrweed (South Africa)
Cadillo (South America)
Sandbur (USA)
Southern Sandbur (USA)

Summary:

A pale green, spiny burred, loosely tufted, annual grass that has prostrate stems that root at the nodes and erect stems with a loose seed head of 5-50 purple, spiny burrs.

Description:

Cotyledons:

One.

Leaves:

Alternate.
Blade - Pale green. 40-250 mm long x 3-15 mm wide. Parallel sided to slightly oval. Stiff. Flat. Often bent or drooping. Rounded at the base and tapering to the tip that often has the edges rolled inwards. Never hairy on the margins and always hairy where the blade joins the sheath, hairy or hairless on the upper surface and rough, usually hairless on the lower surface except near the pointed tip.
Ligule - Hairy ring. 0.5-2 mm long.
Auricles - None.
Sheath - Flattened, keeled. Often hairy on the surface and margins, especially on the lower leaves.

Stems:

150-900 mm long. Pale green. Slender to stout. Sometimes root at the lower nodes. Bent up from lower nodes to an erect section with 3-4 nodes. Forms loose tufts. Often branched. Flattened.

Flower head:

Spike like raceme or panicle of 5-50 spiny burrs, loose to dense, 20-100 mm long x 8-18 mm wide, at the ends of stems. Turns pale brown with age and is often tinged with purple or green. Many, globular to egg shaped, bristly burrs enclose the spikelets. Each burr is 4-10 mm long x 3.5-6 mm wide excluding the bristles and may have a tiny stalk. The outer bristles are 2-5 mm long, hard, barbed, erect or bent backwards but not really interlocking, often purple tinged. The inner, finer bristles are hairy, joined for about half their length at the base and bend inwards but are not interlocking. Below is another ring of downward turned, 4 mm long, bristles.
Burrs fall off at maturity, leaving a rough, zig zag stalk.

Flowers:

Spikelets - 4.5-7 mm long, brown, egg shaped with a pointed tip, 2-4 and sometimes up to 6 per burr. Stalkless.
Florets - Lower one empty or rarely male. Upper floret egg shaped, pointed tip.
Glumes - Thin, membranous, egg shaped with a pointed or rounded tip. First one 1.3-4 mm long, 1 nerved. Second one 3.5-7 mm long, 3-6 nerved, covered with short fine hairs.
Palea - parallel sided to egg shaped, obtuse tip. Similar length to lemma. Covered in fine straight hairs. 2 keels that are rough to touch.
Lemma - The first 3-6.5 mm long, 5 nerved. The second is egg shaped when flattened, 4.5-7 mm long, thin membranous, 5 nerved.
Stamens -
Anthers -

Seeds:

Brownish, egg shaped, 1.6-3.2 mm long x 1.3-2.2 mm wide.

Roots:

Fibrous.

Key Characters:

Ligule a rim of hairs.
No auricles.
Spiny burrs that fall off at maturity leaving a zig zag stem.
Stem bent at lower nodes.

Biology:

Life cycle:

Mainly annual. Germinates at any time of the year with a major germination in autumn and winter in temperate areas or late spring to early summer in subtropical areas. Vegetative growth is rapid and the prostrate stems root at the nodes then send up erect stems that bear the seed head. It flowers from March to August in temperate areas or from January to May in subtropical areas. Most plants die after flowering but some may continue to grow throughout the year.

Physiology:

Reproduction:

By seed and stems rooting at the nodes.

Flowering times:

March to August with some in January in WA.
January to May in QLD.

Seed Biology and Germination:

Seeds can emerge from 90 mm deep in clay soils and 100 mm deep in loamy soils.

Vegetative Propagules:

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

The spiny burr spreads the seed by attaching to wool, fur, clothing and tyres. It also provides buoyancy for spread in water. In irrigation areas this is a major method of dispersal. Contamination of agricultural produce and equipment also helps spread the weed.
It is an aggressive pioneer plant the readily establishes in denuded sandy areas.

Origin and History:

North, Central and South America.
Probably introduced into Queensland around the 1860's.

Distribution:

NSW, NT, QLD, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Humid and subhumid tropical areas.

Soil:

Prefers sandy or light soils.

Plant Associations:

Significance:

Beneficial:

Provides forage when young before the burrs develop.

Detrimental:

Serious weed of maize, sugarcane, cotton, peanuts and pastures.
Weed of rotation crops, perennial crops, orchards, vineyards, vegetables, soybeans, gardens, lawns, disturbed areas, aquatic areas, beaches, river sands, roadsides and footpaths.
Injures workers in and impedes harvesting of crops.
Contaminates wool, injures stock and shearers.
Damages hides.
Causes eye, mouth and foot injuries in stock, dogs and horses.
Injures feet of humans in recreational and working areas.

Toxicity:

Not recorded as toxic.

Legislation:

Noxious weed of NT and WA.

Management and Control:

Thresholds:

It grows rapidly in warm moist conditions, smothering companion plants and competing for light, moisture and nutrients

Eradication strategies:

Prevent seed set by killing plants with cultivation, fire or herbicides before the seed head forms. The extended germination period means this may need to be repeated several times during the year.
Establishing dense competitive pastures and preventing bare areas will reduce the survival of seedlings.
Graze pastures heavily during summer to reduce seed set.
A number of herbicides provide good and selective control in most crops and pastures.

Herbicide resistance:

None reported.

Biological Control:

Related plants:

Birdwood grass(C. setiger)
Buffel grass (C. ciliaris)
Fine bristled Burrgrass (C. brownii)
Gallons Curse (C. biflorus)
Hillside Burrgrass (C. caliculatus)
Spiny Burrgrass (C. incertus, C. longispinus)

Plants of similar appearance:

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P40-41. Diagram.

Ciba Geigy (1980) Grass Weeds 1. CIBA GEIGY Ltd, Basle, Switzerland. P27. 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). #277.5.

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). P947.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P95-97. Photos.

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P35. Diagram.

Acknowledgments:

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