Spiny Emex

Emex australis Steinh.

Synonyms - Emex centropodium, Vibo australis

Family: Polygonaceae.

Names:

Emex is derived from Rumex a closely related genus.
Australis is Latin for southern and refers to its origin in Southern Africa.
Spiny Emex refers to its spiny fruits and membership of the Emex genus.

Other names:

Bullhead
Bindii
Cape Spinach - because it comes from the Cape of Good Hope in South Africa and the young leaves were eaten as spinach.
Cat's Head
Devil's Thorn
Doublegee is derived from the Afrikaans, dubbeltjie or dubbeltjie doorn, meaning devils thorn.
Dubbeltjiedoring (South Africa, Afrikaans)
Duwweltjie (South Africa, Afrikaans)
Emex-dubbeltjie (South Africa, Afrikaans)
Goathead because of the appearance of the prickle when viewed from the side.
Giant Bullhead
Inkuzane (South Africa, Zulu)
Prickly Jacks
Southern Three Corner Jack
Three cornered Jack refers to the 3 spines and Jack refers to its similarity to a 6 pointed metal piece that is picked up while bouncing a ball in children's games.
Tanner's Curse was used in Australia soon after it naturalised.

Summary:

Doublegee or Spiny Emex is a ground-hugging or sprawling herb with 3 pronged prickles. The leaves are ovate, hairless and 20-70 mm long. It forms a rosette of leaves when young then produces sprawling weak vines up to a metre long.
The greenish inconspicuous flowers are in small clusters and are unisexual, but both male and female flowers occur on the same plant. The male flowers have 5 or 6 tiny floral segments and 4-6 stamens. The female flowers are 6-lobed and have 3 styles. The woody fruit is 7-11 mm long with 3 rigid sharp spines.
Native to South Africa, it is a declared pest plant and is a widespread serious weed in agricultural areas and on waste land. It flowers at any time of the year with a flush in spring.

Description:

Cotyledons:

Two. 30-50 mm long and 4-10 mm wide, narrow, midrib obvious on the under side. Tip round. Sides parallel to convex. Base tapered. Surface hairless. Petiole short or none. The seedling has a hypocotyl but no epicotyl.

First leaves:

Grow singly, round to oval or spade shaped, round tip, 55 mm long x 35 mm wide. Tip rounded. Sides convex. Base squarish. Surface hairless. Petiole shorter than the blade, 20 mm long petiole with a membranous sheath at its base.

Leaves:

Form a basal rosette. Alternate. Basal leaves are the longest with leaves becoming progressively smaller along the stem.
Petiole - Usually shorter than leaf blade, 15-140 mm long with a membranous sheath at the base. Lower leaves have longer petioles than upper or stem leaves.
Blade - Dull green, soft, egg shaped to triangular, 20-150 mm long x 12-100 mm wide, flat or indented at the base, somewhat thick and juicy. Older leaf edges are convex and wavy. Tip pointed. Base tapered to squarish or indented. Surface somewhat undulating and hairless.
Sheath - Membranous sheath (ochrea) about 5 mm long at the base of the petiole. Often ragged or has fallen off.
Stem leaves - Alternate. Similar to rosette leaves, tip rounded. On slender stalks, 40-60 mm long. Membranous sheath at base of leaf stalk.

Stems:

Pithy becoming hollow, round, ribbed, smooth, juicy, many from the base and dichotomously or Y branched from some nodes. Prostrate or climbing. Up to 1 m long. Green and often tinged with red or purple at the base and nodes. Turns red-brown on senescence.

Flower head:

Flowers in axillary ring like clusters. Males in a short raceme. Females stalkless forming clusters of spiny burrs.

Flowers:

Inconspicuous, green, about 2 mm wide. Male and female flowers on the same plant and these are self compatible. Flowers of both sexes progressively form from the crown to the tips of the stem. The female flowers are sessile and the male flowers form in short axillary racemes.
Ovary - 3 angled. 3 styles with 3 dilated stigmas.
Perianth - Male; 5-6 equal segments.
Female; Triangular tube, 4-6 mm long with 6 lobes. 3 outer ones ending in a rigid spreading, sharp, 3-6 mm long spine. 3 inner ones are egg shaped, erect, 3-4 mm long with obvious veins, pointed tip and close over the seed. Enlarged and hardened when in fruit.
Stamens - 4-6.
Anthers -

Fruit:

Woody, green turning red brown on maturity and dull black with age, 8 (7-11) mm long x 9.5 mm wide, ribbed, triangular in cross section, 4 pits on each face, 3 sharp spines. The spines are formed from modified lobes of the perianth. When laying on the ground one spine is pointing upward. 1 seed per fruit.
2 types of fruits are formed, one underground at the base of the stem and the other above ground in leaf axils. The underground fruits are initially white with yellow and red, somewhat flattened and tend to remain attached to the crown whereas the aerial fruits are initially green, radially symmetric, detach readily from the crown or stems and also have longer spines. The subterranean fruits are rarely more than 8 mm wide from spine tip to tip. The aerial fruits are usually larger and quite variable in size (even on the same plant) depending on growing conditions.
All fruits turn brown on maturing.
Fruit weights vary from <10 mg to >90 mg with an average of 40-50 mg/fruit.

Seeds:

Triangular pyramid, smooth, glossy, dark brown nut, 2-4 mm long, hairless. Fairly tightly enclosed in the fruit above.

Roots:

Strong, long, thick, fleshy taproot.

Key Characters:

3 pronged, single seeded, woody fruit (achene) with 4 pits on each of the 3 flat faces.
Cotyledons narrowly elliptic and taper at both ends. (cf. linear in E. spinosa).

Biology:

Life cycle:

Annual. Germinates at any time of the year with a flush in autumn and winter. Up to six waves of germination can occur. A deep taproot is quickly formed giving the plant more drought tolerance than most companion species. Under adverse conditions the leaves may wither and the plant re shoots from the rootstock when conditions improve. A basal rosette of leaves forms and a few seeds develop in the crown. The time from emergence to first flowering varies from 4-18 weeks with embryo development starting 3 weeks later and viable seed being produced about 6 weeks after flowering. Long running stems emerge from the centre of the rosette and grow rapidly in warmer weather progressively producing seeds in the leaf axils. The fruits mature in order of formation so ripe fruits may be shedding near the crown while flowers and fruits are still being produced near the ends of the stems. The main flowering starts in late winter and continues until summer drought kills the plant. This is usually 20-32 weeks in Mediterranean environments. In moist or irrigated areas the plant may germinate in summer and successfully complete its life cycle as an annual.

Physiology:

Drought tolerant.
Chromosome number 2n = 20.
There is little genetic variability within or between populations.
Growth rates in glass house conditions are 62-64 mg/g/day dry weight. The first 8 weeks is foliage growth, the next 7 weeks has mainly stem, flower, fruit and root growth with decreased foliage production. After week 15 senescence begins, growth is slow and plant weight is fairly constant as top and root resources are reabsorbed and deposited in the fruits.
Optimum temperature for top growth is 12 degrees C and for root growth is 16.5 degrees C and for development is 19 degrees. Delayed flowering and stem necrosis occurs at 7 and 27 degrees C and no seed was produced at 27 degrees C.
The lower developmental temperature is 0.3 degrees C and the degree days to flowering was 550.

Reproduction:

By seed.
Less than 10 seeds per plant are produced under adverse conditions and up to 1100 in good conditions.
Soil seed banks of up to 17,000 seeds/m2 in experimental conditions and 10,000 seeds/m2 in pasture after crop have been recorded.

Flowering times:

Most of the year in SA.
August in Perth.
Spring in WA.
Mainly in the warmer months in NSW.

Seed Biology and Germination:

Seeds have an after ripening period of 2-6 months. 80-95% of seed can germinate by the autumn following seed set. Some seeds remain non dormant but 60-90% return to a cyclical dormancy with germination occurring only in winter. 5-20% of seed has long term dormancy and won't germinate for at least 2 years.
Field studies indicate that 15-37% of seed germinates in the year after seed set.
Seeds germinate in response to water availability, relatively independently of the temperature.
Seeds remain viable for at least 8 years in soil.
Few seedlings emerge from more than 100 mm deep.
Seed buried 10 mm deep has a greater germination than that on the surface or deeper. Seeds buried 1-5 cm deep are most likely to establish. On undisturbed infested agricultural sites little germination is seen after two years, however, further cultivation leads to many seeds germinating. The effect of cultivation is due to light and aeration.
Seeds on the surface of the soil usually have a low germination percentage.
Over a 4 year experiment with seed buried at 0, 1 and 15 cm deep, 23.5% of seed germinated on the surface, 53.9% germinated at 1 cm deep (80% of these in the first year) and 0% at 15 cm deep. After 4 years, 21%, 10.5% and 18.3% of seed remained viable at the 0, 1 and 15 cm depths respectively.
The woody capsule surrounding the seed reduces the ability of the seed to take up sufficient water for germination.
Emergence rates are greater on more clayey soil than on sands in WA.

Vegetative Propagules:

Hybrids:

Hybridises with Emex spinosa and the progeny resemble Emex spinosa that are self infertile but can backcross to either parent.
There are 2 genotypes in Australia and only one of these occurs in WA 291.

Allelopathy:

Population Dynamics and Dispersal:

Spread by seed that is usually still encased in the spiny fruit. The spiny fruit readily attaches to feet, containers, rubber tyred vehicles including aeroplanes and is transported long distances.
The fruit floats and is dispersed in water flows.
Plant densities of up to 900 plants and 5000 seeds m2 have been recorded, but typical densities vary from 20-500 plants/m2 in infested areas.
At 200 plants/m2 about half the plants will die before seed set.
Germination usually follows rainfall events in the autumn and early winter with up to 6 distinct cohorts. Mid season cohorts often have the greatest number of individuals but early season cohorts usually contribute most to the seed bank if not controlled.
Early rains can lead to germination and the long, large taproot allows it to survive following dry periods better than most associated annual pasture species. This may lead to dominance of the flora and large infestations in subsequent years.
In continuous pastures it tends to decline with time.
It competes mainly for N in cereal crops.

Origin and History:

Native to South Africa.
Introduced to WA as a salad vegetable around 1830 and in hay and produce at later dates. It was in SA by 1840 or 1870, NSW and Victoria by 1883, Queensland in 1911 and NT in 1956.
It has been in New Zealand since 1883.

Distribution:

ACT, NSW, NT, QLD, SA, VIC, WA.
Eradicated in Tasmania but still present on Flinders Island in Tasmania.

Courtesy Australia's Virtual Herbarium.

Habitats:

Prefers nutrient rich, open, disturbed, free draining soils that are neutral to slightly alkaline.

Climate:

Temperate, sub tropical, sub humid tropical and semi arid tropical.
Occurs in areas with an annual rainfall of 200-1000 mm that may be bimodal or summer or winter dominant and with mean annual temperatures of 15-24 degrees C. It is unlikely to persist in regions with a mean monthly temperature less than 0 degrees C.

Soil:

It grows well on sandy and heavy soils and red brown earths as well as a wide range of other soils. The heaviest infestations in WA are on the granite derived red loams. It occurs on soils with a pH range of 4-9. It does not tolerate saline or waterlogged conditions.

Plant Associations:

Capeweed, Clover, Erodium and temperate annual grasses.

Significance:

1 million ha of pasture and 500,000 ha of crop is infested in WA.
It is estimated to cost producers $40M per year in WA.
It is a major weed of crops and pastures across southern Australia.

Beneficial:

Fodder but poorly grazed.
Young leaves used as a cooked vegetable.
Does not host Root Lesion Nematode (Pratylenchus thornei) 64.

Detrimental:

Weed of crops, peas, pastures, lucerne, orchards, vineyards, stock yards, airstrips, gardens, wet areas and disturbed areas.
Contaminant of dried fruit and frozen peas.
Spines may cause lameness in stock, hinder working dogs and reduce the amenity value of recreational sites. Spines can penetrate light footwear and puncture bicycle tyres.
It is a good host for Root Lesion Nematode (Pratylenchus neglectus) allowing some build up of numbers 64.

Toxicity:

May contain toxic levels of oxalate, but only rarely causes stock poisoning.
Infection of wounds from the spiny fruit have led to Black-leg (Clostridium chauvoei) in sheep.

Symptoms:

Oxalate poisoning.

Treatment:

Oxalate poisoning.
Remove stock from dense infestations.
Don't expose hungry, unaccustomed stock to dense infestations.

Legislation:

Noxious weed of NSW, NT, QLD, SA, TAS, VIC, WA.
Noxious weed of New Zealand.

Management and Control:

Establish stable, undisturbed perennial pastures where possible.
Avoid short crop/pasture rotations. Plant densities normally fall quickly in continuous crop.
Tickle cultivate at the break of the season.

Thresholds:

11 plants/m2 have reduced yields by 40% in SA.

Eradication strategies:

The high levels of seed dormancy and longevity make Spiny Emex hard to eradicate.
Manually remove isolated plants and burn them. Spray a 10 m area around them with a mixture of 1 L of Tordon® 75-D® in 100 L of water to help control seeds germinating later in the season.
Small areas should be fenced off to prevent stock, people and vehicles spreading the seed.
For large areas, shallow cultivate in late summer to encourage germination in autumn and then kill the seedlings with cultivation or herbicides. Deep ploughing is not recommended because it buries seed and induces dormancy, which may be broken when the seeds are returned to the surface in following seasons.
Plan for continuous pasture with tactical use of herbicides or plan to use herbicides in the cropping phase. Chemical application usually needs to be applied early and repeated to prevent young plants setting seed before spraying and to control late emerging seed.
In legume based pastures, Broadstrike plus diuron have given the best results in clover based pastures, but rarely provide sufficient control for eradication.
A number of other herbicides and Spray Graze are useful in other situations.
In cereals, the sulfonylurea herbicides or dicamba provide the best control.
Special carpet or wool rollers have been developed to remove Spiny Emex fruit from drying greens for the dried fruit industry.
In bushland areas, wipe actively growing plants with a mixture of 1 L glyphosate(450g/L) plus 2 L water. For small areas, apply a mixture of 0.5 g metsulfuron(600g/kg) plus 100 mL Tordon® 75-D® in 1 L water to actively growing plants before flowering in spring or summer depending on when the Spiny Emex has germinated.
On larger areas, Spinnaker® at 1 L/ha, or 10 mL per 10 L water for hand spraying, will provide reasonably selective control of small actively growing Spiny Emex and control seedlings for about a year. Alternatively, 1 g Broadstrike® plus 100 mL spray oil in 10 L water when the plants are young and repeated every 8 weeks if necessary can be used depending on the main bush species. Inspect areas 3 times a year for several years and repeat control if seedlings emerge.
50 mL glyphosate(450g/L) in 10 L water applied before flowering kills existing plants but tends to leave the area bare and often leads to greater infestations of Spiny Emex. Young plants can be manually removed but older plants tend to break off and regrow. Spiny Emex produces seed very quickly, so early control is essential.
Larger areas in bushland can be selectively controlled with 1 g Broadstrike® plus 100 mL spray oil in 10 L water when the plants are young and repeated every 8 weeks if necessary.

Herbicide resistance:

Biological Control:

Two weevils (Perapion antiquum and Lixus cribricollis) have been released without much success.
The Red Apion weevil (Apion miniatum) is the latest release and has established at a number of sites. With only one generation per year it will take several years before it builds up enough to assess the level of control it will provide.
In Australia, the insects Lophyrotoma analis (a native sawfly) attacks leaves and Brachycaudus rumexicolens (an introduced aphid), Perapion antiquum and Rhinoncus australis (a native weevil) attack leaves and stems.
The diseases Uromyces rumicis attacks leaves and Phomopsis emicis attacks leaves and stems.
Up to 25% of seed may be removed by mice in the field. Major Mitchell Cockatoos, Inland Red-tailed Black Cockatoos, Galahs, Little Billed Corellas and Long Billed Corellas feed on the seed.

Related plants:

Lesser Jack (Emex spinosa) is very similar but has fruits that are half the size and spines that are half as long as Spiny Emex. It is more erect in its growth habit and the young leaves have pointed rather than rounded tips. The cotyledons are longer and narrower and the petiole of the first leaves are longer than the blade.
Emex spinosa has 6-8 pits on each of the 3 flat faces of the fruit compared to 4 pits in Emex australis.
When the fruit is held with the pedicel end pointing towards the ground the short and slender spines are horizontal or downward pointing and the base is truncate with the widest portion near the bottom in Emex spinosa compared to slightly upward pointing, long, robust spines, a rounded base and the widest portion is just below the spines in Emex australis.
When grown together Emex spinosa has more seeds per rosette (8.8 vs 4.7), more seeds per node (6.2 vs 2.2) and more seeds per plant (987 vs 346) than Emex australis. 292.

Plants of similar appearance:

Docks (Rumex spp.) look very similar when young but have don't have 3 spined fruit and usually have erect stems.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P202-203. Photos.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P282. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P229. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P580-581.

Gilbey, D. (1989). Identification of weeds in cereal and legume crops. Bulletin 4107. (Western Australian Department of Agriculture , Perth). P26. Photos.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P198-199. Photo.

Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania). P31. 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). #496.1.

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). P111.

Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P63-66. Diagrams. Photos.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P540-544. Photos.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P134. Diagrams. Photos.

Acknowledgments:

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