Family: Costaceae

Costus scaber, commonly known as spiral head ginger, is a tropical ginger native to Central and South America. It is a showy, upright perennial with broad, spiraling leaves and distinctive cone-shaped flower heads that produce bright orange to red blooms. Because of its bold foliage and ornamental flowers, spiral head ginger is sometimes grown in tropical landscapes and gardens as an accent plant, particularly in moist, partially shaded areas where it can form lush clumps and add visual interest.

In Hawaiʻi, Costus scaber is naturalized on Kauaʻi and Oʻahu and possesses traits that are cause for concern. It can spread readily in favorable conditions, forming dense stands that may outcompete native plants for space, light, and nutrients. These characteristics suggest it could detrimentally impact tropical island ecosystems if its spread continues unchecked. To help protect Hawaiʻi’s unique natural environments, it is recommended to avoid planting spiral head ginger and instead choose a low risk or native alternative that provides similar aesthetic appeal without the ecological risks.

High Risk Traits:

• Elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Thrives in tropical climates
  
• Naturalized on Oahu and Kauai, Hawaiian Islands, and St. Lucia, Caribbean
  
• Other Costus species have naturalized and may be invasive
  
• Shade-tolerant
  
• Tolerates many soil types
  
• Able to form dense thickets that may exclude other vegetation
  
• Seeds, if produced, dispersed by birds and intentionally by people
  
• Able to hybridize with other Costus species
  
• Self-compatible
  
• Able to spread vegetatively by rhizomes

Low Risk Traits:

• Unarmed (no spines, thorns or burrs)
  
• Non-toxic
  
• Ornamental value
  
• Hummingbird-pollinated in native range (may limit seed set where hummingbirds are absent)
  
• Limited seed production may minimize longer distance dispersal