Cenchrus is from the Greek word kenchros for Millet.
Longispinus refers to the long spines on the burr.
Incertus is from the Latin word for uncertain.
Spiny Burrgrass refers to the spiny seed burrs of this grass.
Other Names:
American Burrgrass
Bohena Beauty
Burr grass
Coast Sandbur (Europe)
Dubbelfjiegras (South Africa)
Field Burr
Field Sandbur (USA)
Gentle Annie
Hedgehog grass
Innocent weed
Longspine Sandbur (USA)
Sandbur (North America)
Summary:
A purple/red, tufted annual grass to 600 mm diameter with upward bending stems, up to 800 mm tall, and a cylindrical spiny seed head that is often partially enclosed in the top sheath.
Description:
Cotyledons:
One
Leaves:
Blade - Flat or folded, stiff. 20-200 mm long, 3-14 mm wide. Parallel sided. Tapering to a fine point. Hairless, but often a few hairs where the blade joins the sheath. Smooth or slightly rough to touch especially on the upper surface near the edges and tip. Often with a red or purple tinge. Sometimes twisted and wrinkled. Finely toothed on the edge.
Ligule - Narrow, membranous, fringed with hairs, 1-2 mm long.
Auricles - None.
Sheath - Flattened. Margins are often hairy.
Stems:
Several to many, tufted, upward bending, 150-800 mm tall, from knees at nodes near the base of the plant. Stems at base of plant low lying and branched. Hairless. Flattened especially near base. Roots at basal nodes in contact with soil.
Flower head:
Cluster of spiny burrs. Ring of slender bristles on the outermost series. Cylindrical spike like raceme or panicle, 20-90 mm long by 8-30 mm diameter. Not dense. With up to 40 burrs. Often partly enclosed in leaf sheath. Main axis is smooth to slightly rough to touch, angular and zig zag.
Burrs are straw or purplish colour, egg shaped, 5.5-16 mm long by 2.5-8 mm wide (excluding the spines), split on 2 sides, stalkless, with an outer ring of slender bristles, 2-4 mm long and usually with an inner ring of bristles also. 1-7 spikelets in each burr.
Spines broad at base, rigid, sharply pointed with fine barbs and often bent back on the burr and rough to touch near the tip.
C. longispinus has 40- 70 spines, 5-8 mm long, with 1 deep cleft and purple tinged.
C. incertus has 11-43 spines, 2-5 mm long with 2 deep clefts.
Flowers:
Spikelets - Hairy, stalkless, 3.4-5.8 mm long in C. incertus, 5.8-9 mm long in C. longispinus, often tinged with purple. Surrounded by the burr.
Florets - 1-4 florets per spikelet.
Glumes - First glume 1-4 mm long by 0.6-2.2 mm wide, usually 1 nerved. Second glume 5-7 mm long, 3-7 nerved.
Palea -
Lemma - First lemma 5.5-7.5 mm long, 3-6 nerved. Second lemma 6-8.7 mm long by 2.2-3.5 mm wide, 3 nerved.
Stamens -
Anthers -
Seeds:
In a spiny burr. Egg shaped to oval and flattened on one side. 2-4 mm long by 2-3 mm wide. 1-3 in each burr. Smooth.
Roots:
Fibrous, shallow. Up to 300 mm deep.
Key Characters:
Rigid spiny burrs
Biology:
Life cycle:
Annual. (C. incertus may be perennial).
Seeds germinate mainly in spring to summer and it grows rapidly, especially after heavy summer rains. Burrs produced from December to April. Most plants die in winter but a few may survive and set more seed in spring.
C. incertus may become perennial and re shoot from the crown each year.
Physiology:
Reproduction:
By seed.
Flowering times:
Summer to autumn in NSW
Seed Biology and Germination:
The seed formed first is largest and will germinate in a few months. Others are dormant for up to 3 years.
Up to 1000 seeds per plant produced.
Seed can germinate and establish fro 250 mm deep.
Burrs on the soil surface rarely germinate.
Vegetative Propagules:
Hybrids:
Allelopathy:
Population Dynamics and Dispersal:
Establishment in vigorous pastures is uncommon.
Spines help seed attach to stock and tyres for dispersal and provides buoyancy for dispersal by water.
Commonly spread as a contaminant in hay.
Will establish from seed buried 250 mm deep.
Pioneer plant of open sandy situations.
Origin and History:
North and Central America.
Probably introduced to SA before 1895, VIC before 1895, NSW before 1922 and QLD before 1930.
Distribution:
ACT, NSW, QLD, SA, VIC, WA.
Habitats:
Climate:
Temperate sub humid and semi arid.
Occurs in the 250 -500 mm annual rainfall zone.
Soil:
Sandy, well drained, low fertility soils.
Often occurs in coastal situations.
Unstable sand dunes.
Plant Associations:
Significance:
Beneficial:
Fodder when young before the burrs develop.
Detrimental:
Weed of pasture, disturbed areas, rotation crops, roadsides, orchards, vineyards, lucerne, lawns, irrigation channels and cultivated areas.
Burrs contaminate wool and form prickly mats.
Burrs puncture skin to degrade hides and cause ulcers in sheep mouths. Contaminates dried fruit and produce.
Prevents dogs working stock in infested areas.
Injures shearers and abattoir workers handling burr infested sheep.
Injures workers in horticultural crops.
Toxicity:
Secondary infections may develop from physical damage, especially around the mouth.
Legislation:
Noxious weed of NSW, SA, TAS, VIC and WA.
Management and Control:
Thresholds:
Eradication strategies:
Establish a vigorous and preferably perennial pasture.
Prevention of seeding for 3 years provides good control.
Repeated cultivations are usually required to control plants before they set seed and to control late germinating individuals. Cultivation buries the burr, which stimulates germination. On the sandy soils a combination of cultivation and herbicides is often used to reduce the risks of erosion.
Graze heavily to reduce seed set.
A number of herbicides provide control.
Increasing fertility of the soil, Rhodes grass and Consol Love grass have been used in NSW to reduce Spiny Burrgrass infestations.
A number of herbicides are available for use in various crops and pastures.
Avoid using infested sand or fill for garden or building sites.
Small patches should be eradicated because of it potential to spread.
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)
Mossman River grass (C. echinatus)
Spiny Burrgrass (C. incertus)
Plants of similar appearance:
Compared to Cenchrus longispinus, Cenchrus incertus has shorter spikelets at 3.4-5.8mm long and less spines with 8-40 spines only and they are shorter, less than 5mm, so the spikelets are shorter than the spines and are not tinged. Upper leaf sheaths are less inflated.
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P41-42. Diagrams. Photos.
Black, J.M. (1978). Flora of South Australia. (Government Printer, Adelaide, South Australia). P215.