Family: Fabaceae

Origin, Description & Uses
Leucaena ‘KX2’ (KX2) is a fast-growing hybrid form of leucaena developed from species native to Central America and Mexico. It is a small to medium-sized nitrogen-fixing tree with feathery, bipinnate leaves and a strong ability to thrive in warm, dry to seasonally moist tropical environments. Unlike common leucaena types, KX2 was bred to be largely sterile, which makes it attractive for managed plantings. It is widely promoted for use in agroforestry systems, livestock fodder (browse for cattle and other animals), soil improvement through nitrogen fixation, and as a source of biomass for fuelwood and carbon sequestration projects.

Risks & Threats
Although Leucaena ‘KX2’ is not currently known to be naturalized in Hawaiʻi, it does possess traits that are cause for concern, including very rapid growth, strong competitiveness, and the ability to enrich soils with nitrogen in ways that can favor invasive plant dominance. While sterility reduces the likelihood of spread by seed, uncertainty remains about long-term behavior in tropical island environments and whether limited reproduction or escape from cultivation could still occur under certain conditions. Because of these factors, ongoing evaluation is needed to determine its potential ecological impact in Hawaiʻi. Caution is recommended to ensure that this species does not negatively affect native ecosystems or contribute to unintended environmental changes.

High Risk Traits:

• Broad climate suitability (cool-tolerant, multi-environment)
  
• Nitrogen-fixing (alters soil nutrients)
  
• Produces viable seed (self-sterile but later generations can self-fertile)
  
• Seeds survive gut passage (cattle, other animals)
  
• Persistent seed bank (hard seed coat)
  
• Tolerates cutting, coppicing, and fire
  
• Toxic to animals (contains mimosine)
  
• Allelopathic potential
  
• May form dense thickets (parent species does)
  
• Intentionally planted by people (forage, timber, shade)

Low Risk Traits:

• Mostly self-sterile (F1 hybrids)
  
• Low seed production
  
• No spines, thorns, or burrs
  
• Highly palatable (not unpalatable to grazers)
  
• No human toxicity/allergy known
  
• Difficult to root from cuttings
  
• Unlikely as produce contaminant (seeds relatively large)
  
• Well controlled by herbicides