Family: Fabaceae

Origin, Description & Uses
Senna obtusifolia, commonly known as sicklepod or coffeeweed, is native to tropical and subtropical regions of the Americas. It is a fast-growing annual or short-lived perennial shrub in the pea family (Fabaceae), typically reaching 3–8 feet (1–2.5 m) tall. The plant is recognized by its bright yellow flowers, distinctive curved seed pods, and compound leaves. Throughout its range, it has been used in traditional medicine, as a green manure crop, and occasionally as a coffee substitute made from roasted seeds. It is also sometimes found as a volunteer plant in disturbed areas, pastures, roadsides, and agricultural lands. In Hawaiʻi, Senna obtusifolia has become naturalized on Oʻahu, Lānaʻi, and Hawaiʻi Island.

Risks & Threats
Senna obtusifolia is naturalized in Hawaiʻi and possesses several traits that are cause for concern. It grows rapidly, produces abundant long-lived seeds, and readily colonizes disturbed habitats, agricultural fields, roadsides, and open natural areas. Dense infestations can outcompete native vegetation, reduce biodiversity, interfere with agricultural production, and alter ecosystem processes. Its ability to establish persistent seed banks makes management difficult once populations become established. Because of these invasive characteristics, Senna obtusifolia could detrimentally impact tropical island ecosystems. Where possible, Plant Pono recommends selecting a low-risk or native alternative. Since this species is already established in parts of Hawaiʻi, landowners and landscapers should avoid planting it and prevent its spread into areas where it is not yet widespread to help minimize further environmental impacts.

High Risk Traits:

• Widely naturalized worldwide
  
• Thrives in tropical climates
  
• Serious weed of agriculture
  
• Weedy genus
  
• Potentially allelopathic
  
• Toxic to cattle
  
• Potentially toxic to people
  
• Host for pathogens
  
• Tolerates many soil conditions (and potentially able to exploit many different habitat types)
  
• Forms dense thickets and crowds out other vegetation
  
• Self-pollinating
  
• Can reach reproductive maturity in 1 year
  
• Prolific seed production
  
• Forms a persistent seed bank
  
• Seeds dispersed by water and inadvertently on equipment, animals and as a produce contaminant
  
• Tolerates and resprouts after cutting

Low Risk Traits:

• Shade-intolerant
  
• Used medicinally, and as a source of food (leaves) or as a coffee-substitute (roasted seeds)
  
• Not known to hybridize with other Senna species
  
• Will not spread vegetatively
  
• Herbicides may provide effective control