Family: Fabaceae

Origin, Description & Uses
Macrotyloma axillare, commonly known as perennial horsegram, is a twining or trailing perennial legume native to tropical and southern Africa, islands of the western Indian Ocean, the southwestern Arabian Peninsula, and Sri Lanka. It produces vigorous vines with trifoliate leaves and clusters of small yellow to reddish flowers followed by slender seed pods. Because of its ability to tolerate drought, poor soils, and grazing pressure, perennial horsegram has been used as a forage and pasture species for livestock, as well as for erosion control, soil improvement, and cover cropping in tropical and subtropical regions. Its rapid growth and nitrogen-fixing ability have made it attractive for agricultural and land management purposes.

Risks & Threats
In Hawaii, Macrotyloma axillare is considered potentially naturalizing on Oʻahu and Hawaiʻi Island. This species possesses traits associated with invasive behavior, including vigorous growth, the ability to spread in disturbed habitats, and persistence under a wide range of environmental conditions. As a fast-growing vine, it may smother surrounding vegetation, compete with native plants for light and space, and contribute to changes in plant community structure. Because tropical island ecosystems are especially vulnerable to aggressive introduced species, perennial horsegram could negatively impact native ecosystems if it spreads more widely. Although not yet widespread, its naturalization potential is cause for concern, and planting should be approached cautiously. When possible, choose low risk or native alternatives for groundcover, forage, or soil improvement projects.

High Risk Traits:

• Environmental weed in forests/woodlands; smothers native vegetation
  
• Naturalized in Australia and Hawaii
  
• Climbing, twining growth habit
  
• Shade tolerant
  
• Wide soil tolerance (sands to clays, pH 5.5–7.5, moderate salinity)
  
• Produces viable, persistent seed bank (>1 year)
  
• Self-fertile (cleistogamous flowers)
  
• Flowers and seeds within 1 year
  
• Seeds survive cattle gut passage
  
• Benefits from fire (re-sprouts, enhanced germination)
  
• Intentionally spread by people as forage crop

Low Risk Traits:

• No spines, thorns, or burrs
  
• Not allelopathic, parasitic, or toxic
  
• No vegetative fragmentation
  
• Low seed production (100–150 kg/ha typical)
  
• Poor dispersal by wind, water, birds, or produce contamination