Quick Facts

Quick facts

• Originally from southern Europe and northern Africa, Caltrop (Tribulus terrestris) is a matt forming (prostrate) annual herb with yellow flowers and spiny hard fruit.
• Is a nuisance weed of wasteland, pastoral land, cropping, vineyards and recreation areas, with spiny fruit causing injury to humans, pets and animals
• The spiny hard fruit pierces skin, bike tires and even feet through shoes with thin soles.
• Strategically placed spines on the fruits ensure that it is spread widely by animals and machinery.
• It contaminates orchard crops, dried fruit and wool.
• It is toxic to sheep, causing photo-sensitisation, staggers and nitrate poisoning.
• Control by physical and mechanical removal, and the use of herbicides over many years.

What Does It Look Like?

What is it?

Caltrop (Tribulus terrestris) is a prostrate mat-forming annual herb with yellow flowers and spiny green hard fruits. The stems can be up to 1 m long and spread radially from a central crown with a deep and somewhat woody taproot. The stems are reddish-brown to green, many-branched, and in Australia are invariably prostrate. In other countries the stems may become erect where they are competing with other plants or where they occur in shade. The leaves are compound (pinnate) and usually opposite on the stem. They are unequal in size with the larger having 4-7 leaflet pairs per leaf plus a single apical leaflet, and the smaller with less leaflet pairs or even missing altogether so that the leaves appear to be alternate on the stem. Leaves and stems have a silvery appearance because of the presence of hairs, particularly on the lower surface of the leaflets.

The bright yellow flowers are 5-15 mm in diameter to 10 mm long, opening in the morning. Sepals are about 3 mm long and flowers have five petals, each 5-6 mm  long, which are quickly lost. They are borne singly in the leaf axil (at the junction of the smaller leaf with the stem).

The fruits are nearly spherical woody hard burrs 6-10 mm long, slightly hairy, with sharp rigid spines to about pines 3-8 mm long in the upper part, and 2 shorter spines near the base pointing downwards. At maturity fruits break into 5, wedge-shaped woody nutlets . Each nutlet has a short spines on the exposed surface, a pair of diverging 3-8 mm long spines about the middle of the outer surface and a pair of shorter downward pointing spines on the outer base. These are the dispersal agents for Caltrop and the cause of the problems the species poses (Navie 2004; Barker 2007, pers. comm.) Each fruit segment contains 2-4 small seeds.

Extracts from this species have a number of medicinal uses (PFAF 2004).

Recognition: This species can normally be recognised by the combination of the following characters; prostrate (mat form) fern with pinnate (fern-like ) leaves; yellow flowers 5-15 mm in diameter, with 5 petals; fruits very spiny hard spherical woody burrs 6-10 mm long, slightly hairy, the sharp rigid spines to about pines 3-8 mm long in the upper part, and 2 shorter spines near the base pointing downwards, breaking in to five segments.

For further information and assistance with identification of Caltrop contact the herbarium in your state or territory.

Flower colour

Yellow

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

Caltrop (Tribulus terrestris) occurs within crops and in orchards but mostly in open waste places, such as roadsides, overgrazed pastures, stock yards, roadsides and neglected areas particularly in districts with high summer temperatures and dry sandy soils where there is little competition (Parsons & Cuthbertson 1992).

Are there similar species?

Caltrop (Tribulus terrestris) is a variable species in Australia and its relationships are in need of investigation. Fourteen other species are presently recognised within Australia and debate still occurs regarding if these are native or introduced. They are all superficially similar, Tribulus cistoides, T. eichlerianus, T. minutus, T. micrococcus and T. ranunculiflorus are clearly closely related.

Tribulus cistoides is a more robust version of T. terrestris, found in coastal areas of northern Australia. It has larger flowers (petals more than 15 mm long) and fruits which are more or less without hairs.

Tribulus minutes and T. micrococus are much less robust forms close to T. terrestris, but the nutlets either lack the pair of median spines or are less than 3 mm long.

Tribulus ranunculiflorus is a large-flowered form (petals 15-18 mm long) confined to the Kimberley region (Barker 1998; Barker 2007, pers. comm.).

Tribulus eichlerianus is generally considered to be a native species and it is usually easily distinguished from T. terrestris because of its distinctively shaped and densely pubescent fruits. However as with the other species there is at least one undescribed form that appears as if it might be a hybrid between T. eichlerianus and T. terrestris. Similarly there is a form that appears as if it might be a cross between the native T. cistoides and T. terrestris (Barker 2007, pers. comm.).

Only further studies in the biology of these species, combined with a global review of the variation, is likely to resolve the difficulties encountered in distinguishing between these species. Until that is done there is no way of knowing whether there is any truth in the claims in the weed literature (Parsons & Cuthbertson 2001) that there are native forms of T. terrestris (Barker 1998; Barker 2007, pers. comm.).

Why Is It A Weed?

What are its impacts?

Caltrop (Tribulus terrestris) impacts agriculture and people by growing over and out-competing other plants, and causing injury and damage to people and animals via the large numbers of spiny fruits (nutlets) that each plant produces. A single plant forms a mat-like cover over a relatively large area and may even discourage the growth of other plants through allelopathic (inhibitory) effects (Parsons & Cuthbertson 2001). Spines of caltrop cause injury to fruit pickers, shearers and people around farm buildings, roadsides and recreational areas.

Agriculture: It has become a weed of cultivated crops, orchards, over-grazed pastures, stock yards, roadsides and neglected areas, particularly in areas with high summer temperatures and dry sandy soils where there is little competition. The spiny fruits (nutlets) can injure animals feet of horses, sheep, cattle and dogs. Caltrop foliage is toxic to livestock, especially sheep. Grazing of Caltrop has been associated with nitrate poisoning, photo-sensitisation and sheep staggers (Parsons & Cuthbertson 2001; Naughton & Bourke 2005).  If fruits are eaten by livestock it can damage the mouth and possibly the lining of the stomach and intestines. If they are growing in orchards, vineyards and market gardens they can both be an annoyance to pickers and can contaminate the harvest, particularly cereal or dried-fruit crops. Nutlets may also become embedded in sheep fleeces, lowering their value (Parsons & Cuthbertson 2001). The plant can cause some agricultural loss and its presence may affect land value.

Native ecosystems: Mostly grows in disturbed sites and open areas with little impact on intact native vegetation.  However, it can grow on the edge native vegetation, on the edge of tracks, sometimes in degraded grasslands and open vegetation, nature roadside verges and nature strips.

Urban areas:  It occurs in railway yards, nature strips, parks, and waste areas towns and cities and grows in crack in pavers and car parks in urban areas. Prefers dry sandy soils where there is little competition and will from dense mono-cultures replacing most grasses or ground covers. The spiny fruits (nutlets) can injure people  easily penetrate human flesh, especially those with no shoe on.  Spiny fruits can pierce thin shoe soles, puncture bicycle tyres, and injure domestic animals, normally dogs. They are a particular nuisance to humans on playing fields and caravan parks.

How does it spread?

Caltrop (Tribulus terrestris) are spread by seed only. Because of the spines on the nutlets of Caltrop, they are picked up by animals and by vehicle tyres and subsequently spread about. Due to the architecture of the nutlets, no matter how they are placed on the ground there is always at least one spine pointing upwards allowing them to become embedded into feet, hooves, shoes or tyres – hence they effectively function as "trample burrs" (Parsons & Cuthbertson 2001; Naughton & Bourke 2005; Barker 2007, pers. comm.).

Their propensity to occur in bare areas means that roadsides are particularly good habitats for these plants allowing them to be easily spread by road-works. It is possible that the bare areas are created by the allelopathic (inhibitory) effect of Caltrop which discourages the growth of grass seedlings (Parsons & Cuthbertson 2001). The nutlets can also become embedded in wool and so sheep are also effective dispersal agents (Naughton & Bourke 2005).  Hey can be dispersed by contaminated solid and agricultural horticultural produce and machinery.

What is its history in Australia?

It is not known when Caltrop (Tribulus terrestris) first appeared in Australia. It was first recorded in New South Wales in the 1890s (Parsons & Cuthbertson 2001) and was also recorded in South Australia at this time (Tate 1890). It was possibly introduced in ballast (Kloot 1986). Support for this time frame is given by the fact that it was apparently accidentally imported from the Mediterranean into the United States on livestock and first reported in California in 1903 (Guertin 2005). It is likely that there have been a number of introductions in different parts of Australia (Barker 2007, pers. comm.).

How To Manage It?

Best practice management

Caltrop (Tribulus terrestris) produces large number of seeds per plant and their continuous germination (viability) over a number of years control of Caltrop may be difficult. The prime aim in control has to be reducing the number of seeds produced, reducing the number of seeds stored within the soil and stopping seed dispersal. Watch out for new outbreaks and weed out individual plants as they emerge. If coming from an infested area, be sure to remove any nutlets from footwear, tyres and clothing to prevent further spread (Naughton & Bourke 2005).

Chemical control: Herbicides are most effective at the seedling stage (Parson & Cuthbertson 2001). Application of a registered herbicide via foliar spry is effective. However, any fruits present may contain viable seed. Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au .

Non-chemical control: Physical removal: small seedlings can be hand-pulled and any fruit removed from larger plants  placed in a bag and disposed of in a bin or they could be dried and then burnt, if permitted by local council by-laws.

Mechanical control: Use a prickle roller, matting, foam rubber etc. to pick up mature fruits and dispose of them. Encouraging summer ground cover provides competition for seedlings

Grazing: Caltrop is favoured by bare areas caused by overgrazing or drought.

Cultivation and management: Re-establish ground cover once control has been achieved. Pasture management or renovation to provide competition is often the key to caltrop control in pasture.  Mulching or maintaining a dense turf are the best options to prevent establishment.

Hygiene: prevention is the best form, of control. Make sure that any hay, produce, stock, soil and machinery brought onto any property is free of any nutlets.

Biological control: Caltrop has also been recognised as a target for biological control through a cross-jurisdictional government process. This allows activities to be undertaken to develop effective biological controls. There are a number of native species of Tribulus in Australia and so any potential biological control agents must be carefully tested (Barker 2007, pers. comm.). The larvae of a Native Moth (Ephysteris subdiminutella ferritincta) have been found to attack the seeds of Caltrop, but even though the level of infestation may be quite high, the overall impact of the insect is low. In California Caltrop is apparently controlled by the Stem Weevil (Microlarinus lypriformis) and seed weevil (M. lareynii), introduced from Italy as biocontrol agents in 1961 (Encycloweedia 2005; Parsons & Cuthbertson 2001).

Does it have a biological control agent?

YES

When does it grow? (lifecycle/growth calendar)

Caltrop (Tribulus terrestris) is usually an annual plant germinating after each rain event in late spring and summer. In more northerly and inland areas it is possible that the rootstock is perennial and germination events are more opportunistic. A deep root system is quickly established allowing Caltrop to survive prolonged dry conditions.

Caltrop has seeds that remain dormant in the soil for probably four to five years. They germinate after summer rain and plants grow rapidly, flowering within three weeks of germination and forming new burrs within three to five weeks to six weeks. Individual flowers only last a single day but flowering is usually continuous until there is a decline in temperature with the onset of autumn or if the plant dies. Plants are killed by frosts. Fruit are produced continually throughout this time and it has been estimated that more than a 1 000 seeds can be produced by a single plant; other estimates for the United States give figures of 200-5,000 fruits per plant (Guertin 2003). Buried seed remains viable for many years (Naughton & Bourke 2005).

Where Is It Found?

Which states and territories is it found?

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

What areas within states and territories is it found?

Caltrop (Tribulus terrestris) is widespread throughout all mainland Australian States and Territories, except perhaps for northern Australia where the very similar Tribulus cistoides (also known as Caltrop) is found in coastal areas. It is absent from Tasmania.  It infests vineyards, irrigated cotton, overgrazed pastures and neglected areas. It is densest in areas of habitation and cereal-growing and easily spread along the road network (Parsons & Cuthbertson 2001; Naughton & Bourke 2005; Barker 2007, pers. comm.).

Where does it originate?

The native distribution of Caltrop (Tribulus terrestris) is obscure and the species is very much in need of a global revision. It is generally accepted that it is native to southern Europe and northern Africa but the plant is now so widely spread that this is not certain. It may have originated in the Saharan region, and spread into the Mediterranean region (Squires 1979, cited in Guertin, 2005). However only global DNA studies are likely to be able to suggest where it might have originally been native (Barker 2007, pers. comm.).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NT, SA, TAS, VIC

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Tribulus terrestris

Other scientific names (synonyms)?

• Tribulus terrestis J.W.Green orth. var.
• Tribulus terrestris (long style) R.M.Barker
• Tribulus terrestris (short style) R.M.Barker
• Tribulus terrestris f. long style R.M.Barker
• Tribulus terrestris f. short style R.M.Barker
• Tribulus terrestris var. macrocarpus Rouy
• Tribulus terrestris L. var. terrestris

Does it have other known common name(s)?

Bindi, Doublegee, Bindy Eye (bindii), Bull's Head, Cat's Head, Goat's Head, Puncture Vine, Puncture Weed, Devil's Thorn, Malta Cross, Maltese Cross, Mexican Sandbur, Burnut, Ground Bur Nut, Ground Burnut, Tack-weed.