Family: Asteraceae

Cirsium vulgare, commonly known as bull thistle, is a spiny biennial plant native to Europe, western Asia, and North Africa. It forms a large rosette of deeply lobed, prickly leaves in its first year, followed by tall flowering stems in its second year that can reach over 6 feet tall. The plant produces distinctive purple flower heads that are attractive to bees and other pollinators. Bull thistle was introduced to many regions worldwide, often unintentionally, and has occasionally been used for forage, traditional remedies, or as a nectar source for insects.

Despite its showy flowers, bull thistle is considered an aggressive and undesirable weed in Hawaiʻi. It readily invades pastures, roadsides, disturbed areas, and open natural landscapes, where its dense growth and sharp spines deter grazing and recreation. The plant produces large quantities of wind-dispersed seeds, allowing it to spread quickly and form persistent infestations that are difficult to control. Bull thistle can outcompete native plants, reduce forage quality, and increase management costs for landowners. In Hawaiʻi, it is naturalized on Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Kahoʻolawe, Maui, and Hawaiʻi Island, making ongoing prevention and early control especially important.

High Risk Traits:

• Broad climate suitability
  
• Naturalized worldwide
  
• Agricultural & environmental weed
  
• Spiny → unpalatable
  
• Forms dense thickets
  
• High seed production
  
• Persistent seed bank
  
• Multiple dispersal vectors
  
• Self-compatible & hybridizes

Low Risk Traits:

• Not toxic
  
• Shade intolerant
  
• No vegetative reproduction
  
• Herbicide susceptible
  
• Grazed by some livestock