Family: Cyperaceae

Origin, Description & Uses
Cyperus alternifolius subsp. flabelliformis, commonly known as umbrella sedge, is native to wetlands of Madagascar and parts of tropical Africa. This striking, grass-like plant is characterized by tall, upright stems topped with a whorl of long, narrow bracts that radiate outward like the spokes of an umbrella. It thrives in moist soils, shallow water, and along pond edges, and is widely cultivated as an ornamental for water gardens, containers, and landscape plantings. Its architectural form and tolerance for wet conditions have made it popular in tropical and subtropical regions around the world.

Risks & Threats
Umbrella sedge is naturalized across the Hawaiian Islands, including Kuaihelani (Midway Atoll), Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Maui, and Hawaiʻi Island. This species possesses traits that are cause for concern: it grows rapidly, produces abundant seeds, and spreads vegetatively, allowing it to form dense stands in wetlands and riparian areas. These thick colonies can crowd out native wetland plants, alter habitat structure, and interfere with natural water flow. Because tropical island ecosystems are especially vulnerable to aggressive aquatic and semi-aquatic plants, umbrella sedge could detrimentally impact sensitive habitats and reduce native biodiversity if not carefully managed.

High Risk Traits:

• Naturalized in Hawaii, Pacific Islands, California, and tropical regions
  
• Weed of cotton (Australia)
  
• Environmental weed (Florida, Queensland)
  
• Congeneric weeds exist in genus
  
• Host for sugarcane pest Eldana saccharina
  
• Tolerates sun to shade
  
• Rhizomes; reproduces vegetatively
  
• Intentional ornamental introductions
  
• Propagules water-dispersed
  
• Prolific seed production
  
• Resprouts after cutting or frost

Low Risk Traits:

• Restricted to moist/wet soils; narrow pH range
  
• Non-toxic to animals or humans
  
• No spines, thorns, burrs
  
• Unlikely fire hazard
  
• No persistent seed bank