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Tribulus cistoides L. 1753
pronounced: TRY-bew-luss kiss-TOY-deez
(Zygophyllaceae– the caltrop family)
common names: Caltrop, Goat’s Head Burr, Puncture Vine
Caltrops are devices with 4 metal points arranged so that when any 3 are on the ground, the 4th spike projects upwards. This was a weapon used in mediaeval times by foot soldiers to slow down attacking cavalry. Handfuls of caltrops were thrown down in the path of the horses, and the upward-pointing spikes damaged the hooves. It was not a new invention in the Middle Ages. Roman soldiers had used a similar weapon in classical times, but they called it a tribulus. The Romans gave the same name to a water-plant that had a prickly nut, and Linnaeus used that name for this genus. Devices working on a similar principle to the caltrop are still used in some places by police, to puncture the tyres of would-be escaping vehicles. The word caltrop comes from an Old English word calcatræppe, ‘foot-trap’. The burr from this plant certainly has similarities. Cistoides is thought to be derived from the Latin cisthos, the name given by Pliny the Elder in his Naturalis Historia to a shrubby plant with red blossoms.
The plant is native to tropical America, but because of its tolerance to salt and drought conditions, it has been used extensively as a ground cover in coastal landscapes in the USA, particularly in Florida. Its spiny fruits are very much a ‘thorn in the flesh’ for many cyclists, gardeners and animals. The burrs are sharp enough to puncture bicycle tyres, and are painful to step on with bare feet. The plant invades dunes, coastal lands, sandy sites, median strips, roadsides, and disturbed sites. In 2010 it had a particularly good year on Magnetic Island. Ironically, since it was introduced there by the authorities, in Florida it has joined the enormous list of noxious invasive species.
This is a perennial herb, prostrate to ascending, with opposite, pinnately compound, 15 cm long leaves. These are divided into 5–8 pairs of elliptic leaflets ranging from 6 to 12 mm long. The flowers are solitary, bright yellow, 3–4 cm across, and 5-petalled. Spiny fruit about 12 mm wide are produced after flowering. The seeds are spread easily by machinery, animals and humans. The spiny seeds become caught in tyres or in animal fur, aiding the spread. The seeds are very persistent in the environment, and can remain dormant in the soil for up to 5 years.
Despite this plant’s bad qualities, it does have medicinal uses, treating ailments such as headache, nervous disorders, and constipation.
The plant is host to the larvae of several Lepidoptera species, including:
Information about medicinal qualities of plants, or about their use as medicines, is for interest only, and is not intended to be used as a guide for the treatment of medical conditions.
Photographs taken in Picnic Bay 2010
Page last updated 10th March 2018