Family: Zygophyllaceae

Origin, Description & Uses
Tribulus terrestris (puncturevine), also known as goathead or caltrop, is a low-growing, sprawling annual plant native to parts of Europe, Asia, Africa, and Australia. It thrives in hot, dry environments and is commonly found in disturbed areas such as roadsides, vacant lots, agricultural fields, and sandy soils. The plant produces small yellow flowers followed by distinctive woody seed pods covered with sharp, rigid spines. Puncturevine has a long history of use in traditional medicine and is sometimes sold as an herbal supplement, although scientific evidence supporting many of its claimed health benefits is limited. It is also occasionally found as a weedy component of pastures and other open landscapes.

Risks & Threats
Tribulus terrestris is naturalized on Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Maui, and Hawaiʻi Island. It possesses several traits that make it a high-risk invasive species, including prolific seed production, long-lived seeds, rapid establishment in disturbed habitats, and highly effective dispersal by people, vehicles, livestock, wildlife, and equipment. Its sharp, spiny fruits can injure people and animals, puncture bicycle and vehicle tires, contaminate agricultural products, and discourage recreation in infested areas. The species readily colonizes open, dry habitats where it can outcompete desirable vegetation and contribute to the degradation of tropical island ecosystems. Because puncturevine is already widespread in Hawaiʻi, preventing its spread into uninfested areas and controlling existing populations where feasible are important steps to minimize further impacts. When selecting plants for landscaping or restoration, choose low-risk or native alternatives whenever suitable options are available.

High Risk Traits:

• Broad climate tolerance (tropical to temperate)
  
• Naturalized in Hawaii; troublesome weed in Australia, pastures, and croplands
  
• Naturalized on all main Hawaiian Islands (Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Maui, and Hawaiʻi)
  
• Spiny burrs attach to animals, people, and vehicles
  
• Toxic to livestock (sheep especially); causes liver damage and death
  
• Prolific seed production (up to 5,000 seeds/plant)
  
• Persistent seed bank (>1 year)
  
• Multiple dispersal vectors (external attachment, produce contaminant, human transport)
  
• Self-compatible; no specialist pollinator required
  
• Annual; matures within 1 year

Low Risk Traits:

• Not an environmental weed (no known natural ecosystem impacts)
  
• Intolerant of shade
  
• No vegetative reproduction
  
• Well-controlled by herbicides and shallow cultivation