Family: Fabaceae

Origin, Description & Uses
Macroptilium atropurpureum, commonly known as siratro, twining cow pea, or vining cow pea, is a fast-growing perennial vine native to Mexico, parts of Central and South America, and Tobago. It has long trailing stems, purple pea-like flowers, and trifoliate leaves that resemble other cowpea relatives. Because of its vigorous growth and ability to fix nitrogen in the soil, siratro has been widely introduced throughout tropical and subtropical regions as a forage crop for livestock, a cover crop, erosion control plant, and green manure in agricultural systems. It is well adapted to dry and disturbed environments and is commonly planted in pastures and along roadsides.

Risks & Threats
Siratro is naturalized on Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Kahoʻolawe, Maui, and Hawaiʻi Island. This species possesses traits that are cause for concern, including rapid growth, prolific seed production, and the ability to spread aggressively over surrounding vegetation. Its dense, twining growth can smother low-growing native plants and alter open habitats, particularly in disturbed areas, coastal zones, and dry ecosystems. Because it is capable of persisting and spreading across a wide range of environmental conditions, it could detrimentally impact tropical island ecosystems by competing with native vegetation and contributing to habitat degradation. When possible, choosing a low risk or native alternative is recommended, especially for landscaping, erosion control, or pasture improvement projects in Hawaiʻi.

High Risk Traits:

• Naturalized beyond native range
  
• Environmental weed (smothers native vegetation)
  
• Host for recognized pests and pathogens (e.g., nematodes, rust fungi)
  
• Tolerates a wide range of soil conditions
  
• Climbing or smothering growth habit
  
• Produces viable seed
  
• Self-compatible
  
• Minimum generative time: 1 year
  
• Propagules dispersed intentionally by people
  
• Propagules survive passage through the gut
  
• Prolific seed production (>16,000 seeds/m²)
  
• Forms a persistent seed bank (>1 year)
  
• Well controlled by herbicides (indicates resilience, but treatable)

Low Risk Traits:

• No spines, thorns, or burrs
  
• No allelopathic evidence
  
• Palatable to grazing animals (high)
  
• Not toxic to animals or humans
  
• Not shade tolerant
  
• No vegetative fragmentation in nature
  
• Not adapted to wind, water, or bird dispersal