this grass grows throughout the world in tropical and subtropical areas. it was introduced to the united states in seed for forage grasses and probably in ballast water from ships. it was also imported by the united states department of agriculture to grow as a forage grass for cattle. it was deliberately planted throughout southern florida and it easily escaped cultivation, eventually becoming "one of the most serious weeds in florida," spreading to more than 70% of the waterways in the state. in lake okeechobee it has invaded more than 16,000 acres of marsh. it displaces native plants, growing colonially in thick monotypic stands. dense mats or stands of the grass cause hypoxia in the water. torpedograss management in flood control systems costs an estimated us$2 million per year.