Family: Asteraceae

Centaurea melitensis, commonly known as cockspur thistle or Maltese star thistle, is an annual thistle native to the Mediterranean region. It typically grows 1–3 feet tall and is easily recognized by its bright yellow flower heads surrounded by sharp, rigid spines. The plant thrives in dry, disturbed areas such as roadsides, pastures, and fallow fields. Historically, it has had very limited use, mostly as a minor ornamental curiosity or accidentally introduced as a contaminant in seed or forage rather than for any intentional agricultural or landscaping purpose.

Despite its striking flowers, cockspur thistle poses notable risks where it becomes established. It spreads readily by seed and can form dense infestations that displace native plants and desirable forage species. Its sharp spines deter grazing, reducing pasture value and hindering land access for people and animals. In dry environments, heavy infestations can also contribute to increased fire risk by adding fine, dry fuels. Because of these impacts, Centaurea melitensis is considered an invasive or noxious weed in many regions, and prevention, early detection, and active management are important to protect native ecosystems and agricultural lands.

High Risk Traits:

• Broad climate suitability, and elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Grows in tropical climates
  
• Naturalized on all the main Hawaiian Islands; widely naturalized elsewhere
  
• A disturbance adapted weed that may impact agriculture
  
• An environmental weed in California, threatening native ecosystems and an endangered plant species
  
• Other Centaurea species are invasive
  
• Spiny bracts may deter browsing
  
• Suspected of causing a neurological disorder in horses (confirmation needed)
  
• Tolerates many soil types
  
• Forms dense thickets
  
• Reproduces by prolific seed production
  
• Cleistogamous (capable of self-pollination)
  
• An annual or biennial herb, capable of reaching maturity in <1 year
  
• Seeds readily dispersed by wind, water, internally and externally by animals, and accidentally by humans as a seed contaminant and attached to vehicles and equipment
  
• Seeds may persist in the soil for 4 to 10 years
  
• No natural enemies present in the Hawaiian Islands

Low Risk Traits:

• Primarily a weed of dry, disturbed habitats in the Hawaiian Islands
  
• Palatable to browsing animals (although spiny bracts may deter browsing)
  
• Not reported to spread vegetatively
  
• Herbicides provide effective control
  
• Mechanical control methods and fire may be effective at certain growth stages