Tribulus terrestris Seeds | Puncture Vine
LATIN NAME: Tribulus terrestris
COMMON NAME: Puncture Vine
Plant Profile
The whole plant is built for bare, disturbed, sun-baked ground. Stems radiate prostrate from a slender taproot, lying flat and reaching out to a metre, and each plant can cover a wide circle of soil. Leaves are pinnate, with four to eight pairs of small leaflets, and they close up in dull weather.
The flowers are small, yellow and five-petalled, carried singly in the leaf axils, and they open only in full sun, which is why a patch looks bare on a cloudy morning. Pollination is by small bees and flies, and the fruit follows quickly, hardening as it ripens.
Each fruit breaks apart into four spiny nutlets, occasionally five, and each nutlet carries a pair of long spines and smaller ones between them. There is no wind or animal vector involved: the burrs simply attach to whatever passes, whether that is a sheep’s fleece, a boot sole or a bicycle tyre. Dispersal is a by-product of being walked on.
That sun-dependence is a useful identification character in the field. Puncture vine is at its most conspicuous around midday in summer, when the yellow flowers are wide open over prostrate grey-green mats, and at its least conspicuous in the early morning or under cloud.
Puncture vine is listed as a noxious weed in parts of North America, and the listing is largely about the fruit rather than competition with crops. Its economic bite is aimed at tyres, livestock and bare feet. Against it, two weevils have been introduced as biological control agents: one works in the seed heads and one bores the stems, and together they have reduced populations on some western sites.
Science & Biotechnology
The plant’s chemistry is dominated by steroidal saponins, among them protodioscin and dioscin, with related furostanol and spirostanol compounds in the aerial parts and the fruit. Dioscin is a glycoside of diosgenin, the spirostanol sapogenin that underpinned the early steroid industry when yam tubers were its main source, and that chemical kinship is the reason puncture vine keeps appearing in the research literature.
Where stock graze it heavily, the plant is a genuine hazard rather than a curiosity. Outbreaks of photosensitisation with liver damage have been recorded in sheep on dry pastures in southern Africa, and the saponin content is the suspected cause. Animals on bare, overgrazed ground are the ones most likely to eat enough of it.
Uses & Benefits
Extracts of the fruit are sold for athletic performance and for testosterone support, and the research line behind the marketing is real but modest. Trials in trained men have generally failed to show a rise in testosterone, and the few positive reports are small. The honest position is that the saponins are well characterised, the extract is widely traded, and the clinical claims run well ahead of the evidence.
Growing from Seed
Grown deliberately, it is a curiosity for a hot, gravelly bank where nothing else will grow, and the flowers are neat if you are on your knees. Grow it in a large pot or a bottomless bucket sunk into the ground unless you want it in the paths, and pick the fruit before it dries if the neighbours have bicycles. Wear gloves when you pull it up, and put the pulled plants in a bag rather than on the compost heap, because the fruit survives a season in the heap and comes back with the mulch.
Sow on the surface of a sandy mix with a high proportion of grit, cover about 3 mm, and keep the pan on the dry side; the plant resents rich compost far more than it resents drought. Thin the seedlings when they are large enough to handle, leaving the plants a hand’s span apart, and never feed them.
The mat tells you when to thin: once the stems of neighbouring plants begin to overlap, the patch is too dense and the fruits will be crowded at the edges. Lift surplus plants while the stems are still short, and pull any that stray beyond the bed before the fruit colours.
Our Take
Puncture vine is a plant to grow with gloves and a plan, and to read about before you grow it. Growers interested in the same class of compounds usually look at fenugreek, whose seeds also carry steroidal saponins, or at the Chinese yam that gave the steroid industry its starting material; liquorice shows how far a different saponin can travel in trade.
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