- A wetland rush with long, thick leaves
- Flower is brown and shaped like a cigar, seeds spread by wind
- Long stem grows underground into a creeping mat
- Native to Eurasia, Africa, and North America, introduction history in Hawaii unknown. First discovered on Oahu in 1979
- One flower head can produce 250,000 seeds, which spread by wind and are viable for 100 years
- Underground runners can produce new plants
- Takes over wetlands, crowding out native plants and destroying native waterbird habitat (leaving endangered Hawaiian stilt and koloa duck homeless)
- Threatens the taro industry as it invades loi (taro patches). Difficult and costly to reclaim infested areas for taro production
- Kauai: Populations in Mahulepu, Niumalu, Kealia, Nukolii, Puhi, Waimea Valley, Koloa and Hanapepe. KISC is working to control as many populations as possible, but asks that landowners help by controlling this pest wherever possible. Call KISC for control advice.
- Oahu: Fresh water areas near Pearl Harbor, Kawainui Marsh, limited areas along Punaluu, and other sites. Landowners are asked to control where possible.
- Maui: One small patch known from canal between Kanaha Beach Park and Kahului Airport.
- Molokai: None known.
- Lanai: Presence/absence unknown
- Kahoolawe: None known.
- Big Island: Presence/absence unknown.