Family: Fabaceae

The pink shower tree, also known as carao, is a stunning flowering tree native to the neotropics, ranging from southern Mexico through the Amazon basin. Reaching heights of up to 60 feet, it is characterized by a wide, umbrella-shaped canopy and pinnate leaves that are green on top and a distinctive maroon underneath. In early spring, the tree creates a “show-stopping” display as its branches become engulfed in clusters of pastel pink and coral flowers, often blooming while the tree is briefly leafless. Beyond its ornamental beauty, the tree has deep roots in traditional medicine and Caribbean culture; the long, woody seed pods contain a dark, honey-like pulp that is used as a natural iron supplement to treat anemia and as a gentle laxative. The durable wood is also prized in its native range for cabinetry and home construction.

From an ecological perspective, Cassia grandis is generally considered a low-risk species for Hawaii. Unlike some of its relatives, it does not spread aggressively because its large, heavy pods require specific (and now largely extinct) animals for dispersal; today, the pods typically rot where they fall unless moved by humans. However, there are practical considerations for urban planting: the ripened pods are quite large (up to 20 inches) and can be messy when they drop on sidewalks or driveways. Additionally, the pulp inside the pods has a very strong, pungent odor—often described as “stinking toe”—which may be unpleasant in high-traffic areas. For those seeking the floral beauty without the heavy pod litter, the sterile hybrid Rainbow Shower (Cassia x nealiae) is often recommended as a cleaner alternative.

High Risk Traits:

• Broad Climate Suitability: Suited to tropical/subtropical climates
  
• History of Repeated Introductions: Intentionally planted in many regions outside its native range (Asia, Africa, USA, Oceania).
  
• Evidence of Naturalization: Possibly naturalized in some areas (e.g., St. Croix, St. Thomas).
  
• Nitrogen Fixing: can alter soil nutrient dynamics, potentially favoring its own growth over native species.
  
• Produces Viable Seed: Seeds are hard-coated and can persist, with dormancy mechanisms.
  
• Forms Persistent Seed Bank: Evidence of seed longevity >1 year.
  
• Tolerates Disturbance: Can sucker and regenerate rapidly after mutilation or fire.
  
• Palatable to Animals: Fruits are eaten by cattle, which could aid in local dispersal.

Low Risk Traits:

• Not a Weed: No evidence of being agricultural, environmental, or garden weed.
  
• No Toxic or Allelopathic Effects: Not toxic to humans or animals; no allelopathy reported.
  
• Not Shade Tolerant: Prefers full sunlight; not adapted to understory conditions.
  
• Not a Climber/Smothering: Grows as a single-trunked tree, not a vine or thicket-former.
  
• Limited Dispersal: Large seeds not adapted for wind, water, or animal dispersal; low unintentional spread risk.
  
• No Prolific Seed Production: Does not produce high seed densities.
  
• Requires Scarification for Germination: Seed coat hardness limits natural germination.
  
• Not Fast-Reproducing: Minimum generative time is 4+ years.