About Panicum repens L.
Panicum repens is a grass species with many common names, including torpedo grass, creeping panic, panic rampant, couch panicum, wainaku grass, quack grass, dog-tooth grass, and bullet grass. Its exact native range is not clear; different sources state it is native to "Africa and/or Asia", "Europe or Australia", "Eurasia", "Australia", "Europe, Asia, and Africa", or other specific regions such as the Mediterranean and Argentina. It occurs as an introduced species in many regions, where it is often a noxious weed, and has been described as "one of the world's worst weeds."
This grass grows across the globe in tropical and subtropical areas. It was introduced to the United States via forage grass seed and likely in ships' ballast water. It was also imported by the United States Department of Agriculture to be grown as cattle forage, and was deliberately planted throughout South Florida. It easily escaped cultivation, eventually becoming "one of the most serious weeds in Florida", spreading to over 70% of the state's waterways. In Lake Okeechobee, it has invaded more than 16,000 acres of marsh. It grows in thick, monotypic colonial stands that displace native plants, and dense mats and stands cause water hypoxia. Managing torpedo grass in flood-control systems costs an estimated US$2 million per year.
The plant is established in sandy coastal habitats on the U.S. Gulf Coast from Florida to Texas, including beaches and dunes, where it grows alongside beach plants such as turtleweed (Batis maritima), saltgrass (Distichlis spicata), marsh fimbry (Fimbristylis spadicea), largeleaf pennywort (Hydrocotyle bonariensis), and dwarf saltwort (Salicornia bigelovii). It grows on many barrier islands, and occupies many types of wetland habitat, both in and out of water, including freshwater marshes, salt marshes, mud flats, wet prairies, tide pools, bogs, and lakesides. It also invades drier habitats such as coastal pine forests and white sand scrub, and readily spreads into disturbed and cultivated areas like ditches and canals. It is a nuisance in sod production, and can be found in turf and orchards in other regions; in the Florida turfgrass industry, it is the second-worst known weed. While the grass can grow in a wide variety of habitats, it does not tolerate cold, and is rarely found above subtropical latitudes or at altitude.
