​​Caltrop​

Other Common Names: Catshead, Bindii, Doublegee, Puncture Vine, Maltese Cross, Mexican Sandbur, Burnut, Ground Bur Nut, Tack-weed, Yellow Vine. 

Seeds can remain dormant in the soil for 4 to 5 years and typically germinate following summer rain. Plants reach maturity within 0 to 1 year. Fire can help reduce the number of viable seeds in the soil seed bank.

• Deep taproot.
• Somewhat woody.
• Arises from a central crown. 

Usually grows as an annual plant, germinating after rain in late spring and summer. In northern and inland areas, plants may persist from a perennial rootstock. Plants develop a deep root system quickly, allowing survival during prolonged dry conditions. Flowering and fruit production continue through warm conditions and generally cease with autumn cooling. Plants are killed by frost.

Similar native species: ​​Similar to several native species, including Tribulus eichlerianus, Tribulus cistoides and Tribulus ranunculiflorus. T. eichlerianus is usually easily distinguished by its distinctively shaped and densely pubescent fruits, whereas Caltrop has less hairy fruits with prominent spines. T. cistoides is a more robust coastal species with larger flowers (petals over 15 mm long) and fruits that are almost hairless, compared to the smaller flowers and spiny fruits of Caltrop. T. ranunculiflorus (confined to the Kimberley region) also has large flowers (15–18 mm petals), making it noticeably different from the smaller-flowered Caltrop​ 

Similar non-native species: ​​Similar to other introduced species such as Tribulus minutus and Tribulus micrococcus. These species differ by having nutlets that either lack the pair of median spines or have spines less than 3 mm long, whereas Caltrop typically has well developed spines.​ 

​​Dispersal of the burrs via tyres, water, machinery, soil movement and adhesion to animals, clothing, footwear. Burrs attach easily ​onto almost any object that is placed on it. 

Mainly a weed of disturbed and open areas, including degraded grasslands, track edges, roadside verges and urban environments. In bushland, it can invade areas with little ground cover or competition, where it may form dense mats that replace grasses and other ground-layer plants. Its spiny fruits are also a nuisance in recreational and natural areas, causing injury to people and animals.

Introduced as a seed contaminant in seed from Europe to Southern Australia. First record in Australia was in the 1890’s in New South Wales. Likely that there have been a number of introductions in different parts of Australia.