Family: Brassicaceae

Origin, Description & Uses
Rapistrum rugosum (bastard cabbage) is an annual herb in the mustard family (Brassicaceae) native to a wide region spanning Macaronesia, the Mediterranean Basin, Central Asia, Iran, northeastern tropical Africa, and the Arabian Peninsula. It typically grows as an upright, branching plant with lobed leaves and small yellow flowers characteristic of many wild mustards. The species thrives in disturbed soils, roadsides, pastures, and agricultural areas. While not widely cultivated as a crop, it is sometimes recognized as a wild edible or considered a minor forage plant in some regions, though it is generally treated as a weedy species rather than a valued horticultural plant.

Risks & Threats
In Hawaiʻi, Rapistrum rugosum is naturalized on Kauaʻi, meaning it is now reproducing and persisting in the wild without cultivation. As a member of a highly adaptable mustard group, it is capable of spreading quickly in disturbed habitats and competing with native and beneficial plant species. Its ability to produce abundant seed and tolerate a range of environmental conditions raises concern for further spread into natural and agricultural areas. Although its full ecological impact in Hawaiʻi is still being assessed, it possesses traits that are cause for concern. Ongoing evaluation is needed, and caution is recommended to ensure it does not negatively impact Hawaiʻi’s ecosystems or biodiversity.

High Risk Traits:

• Broad climate suitability (environmental versatility)
  
• Naturalized outside native range
  
• Garden/amenity/disturbance weed
  
• Agricultural/forestry/horticultural weed
  
• Tolerates a wide range of soil conditions (pH 4–10)
  
• Produces viable seed
  
• Propagules likely dispersed unintentionally
  
• Propagules likely disperse as a produce contaminant (e.g., grass seed mixes)
  
• Forms a persistent seed bank (>1 year)
  
• Herbicide resistance documented (e.g., chlorosulfuron, atrazine)

Low Risk Traits:

• No spines, thorns, or burrs
  
• Not allelopathic (unknown, but no evidence)
  
• Palatable to grazing animals (goats)
  
• Not toxic to animals or humans (no evidence)
  
• Not shade tolerant
  
• Self-incompatible
  
• No vegetative reproduction by fragmentation
  
• Minimum generative time: 1 year (annual)