Family: Asteraceae

Origin, Description & Uses
Sonchus oleraceus (common sowthistle) is native to Macaronesia and a broad region spanning Europe and the Mediterranean, extending through the Sahara and into the Arabian Peninsula. It is a fast-growing annual herb in the aster family, commonly found in disturbed areas, roadsides, gardens, and agricultural fields. The plant produces soft, lobed leaves and bright yellow, dandelion-like flowers that form wind-dispersed seed heads. Like other sowthistles, it contains a milky sap and is sometimes used as a traditional edible green or potherb, and may also be browsed by livestock in some regions.

Risks & Threats
This species is naturalized across the Hawaiian Islands, including Kaʻula, Mokupāpapa (Kure Atoll), Niʻihau (including Lehua), Kuaihelani (Midway Atoll), Kauaʻi, Manawai (Pearl & Hermes Atoll), Oʻahu, Molokaʻi, Lānaʻi, Kahoʻolawe, Lalo (French Frigate Shoals), Maui, and Hawaiʻi Island. Sonchus oleraceus possesses traits that are cause for concern, including rapid growth, high seed production, and wind-dispersed seeds that allow it to spread quickly across open and disturbed habitats. It can form dense populations that compete with native vegetation and complicate restoration efforts, particularly in sensitive coastal and island ecosystems. As a widespread naturalized weed, it could detrimentally impact tropical island ecosystems by displacing low-growing native plants and altering habitat structure. When possible, choose low-risk or native plant alternatives, and in areas where it is already established, focus on preventing further spread into less-infested natural areas to minimize additional ecological impacts.

High Risk Traits:

• Broad climate suitability and elevation range
  
• Widely naturalized worldwide, including all main Hawaiian Islands except Niihau
  
• A disturbance-adapted weed that impacts several crops
  
• An environmental weed, identified as one of the weed threats to the endangered Hawaiian plant Peucedanum sandwicense
  
• Other Sonchus species are invasive
  
• Potentially allelopathic
  
• May be toxic to lambs and horses
  
• Host of several economically important plant pests and parasites
  
• Tolerates many soil types
  
• Forms dense patches that can exclude other vegetation
  
• Reproduces by seeds
  
• Self-compatible
  
• An annual, able to reach maturity in one growing season
  
• Seeds dispersed by wind, water, by adhering to animals, vehicles, other machinery, as a produce contaminant, and internally by animals
  
• Capable of prolific seed production
  
• Seeds may persist in the soil for one year in the field, and possibly longer

Low Risk Traits:

• Typically invades disturbed or degraded habitats rather than intact native ecosystems
  
• Unarmed (no spines, thorns, or burrs)
  
• Palatable to livestock (in spite of possible toxicity)
  
• Shade intolerant
  
• Certain herbicides may provide effective control