Torpedograss is native to both the Old and New Worlds [44], with reported sources of origin including southern Europe [105], the Mediterranean, the Arabian Peninsula, Israel [29], northern [29], tropical, and southern Africa [29,105], Argentina [29], and Australia [29,109].
Torpedograss was introduced to the Gulf Coast of the United States sometime prior to 1876, when it was first collected in Alabama [65]. It was introduced in seed for forage crops [65,69]. Seed may also have been transported via ballast from sailing vessels carrying lumber from the Mediterranean [109]. In the early 1900s the United States Department of Agriculture imported and distributed torpedograss seed to provide forage for cattle [69]. By 1950, it was planted in nearly every southern Florida county and in a few central and north-central counties [65]. It subsequently escaped cultivation [29].
As of this writing (2011), torpedograss occurs in tropical and subtropical regions throughout the world from latitude 35 °S to 43 °N [49]. In the United States, the distribution of torpedograss is limited to the southern Atlantic coast from North Carolina south and west to Texas, and isolated populations in California and Hawaii [58]. It also occurs in Mexico [11]. Plants Database provides a distributional map of torpedograss.
It is not clear what fire regime torpedograss is best adapted to. Observations from Florida suggest that fire severity may impact torpedograss survival, with high-severity fires potentially killing torpedograss rhizomes [7]. Repeated fires have resulted in torpedograss mortality in some situations, but torpedograss has survived repeated fires under other conditions (see Plant response to fire). Alteration of local fuel characteristics following torpedograss invasion may change FIRE REGIMES.
In North America, torpedograss invasion is limited to relatively few plant communities, many of which lack fire regime information. See the Fire Regime Table for available information on FIRE REGIMES of vegetation communities in which torpedograss may occur. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Fire adaptations: Torpedograss exhibits some characteristics that enable it to survive fire. It is rhizomatous (see Vegetative regeneration), and managers report that rhizomes below the soil surface generally survive fire ([7], personal communication [6]). Torpedograss also often establishes in moist to wet areas where rhizomes are generally protected from fire damage, though aerial portions may burn [7]. Torpedograss has been observed sprouting following fire [45,46,92,98] (see Plant response to fire, below), herbicide application [14,39,54,59,83,92], grazing [79], cutting, [19,39], and plowing or disking [83,92]. However, rhizomes show some sensitivity to heat, so high-severity fire may kill rhizomes [7]. Growth chamber experiments showed that rhizomes died after 1 hour of immersion in heated water (>140 °F (60 °C)) [109].
As of this writing (2011), the limited available information suggests that torpedograss is not particularly adapted to establishing in burned areas via dispersed seeds or from the soil seed bank (see Seed production, Seed banking, and Germination).
Plant response to fire: The available information suggests that torpedograss biomass is reduced following fire but plants often survive and sprout quickly. Mortality may occur in areas where local conditions (e.g., moisture, soil depth) expose rhizomes to heat. Postfire recovery is likely, though recovery may be limited in areas that experience flooding or are treated with herbicides.
Several sources report torpedograss surviving and sprouting soon after fire in Florida. One manager in Florida observed that torpedograss exhibits faster postfire recovery than native plants, allowing it to dominate burned areas at the expense of native vegetation (personal communication [6]). Managers report that in areas around Lake Okeechobee where water depth was approximately 2 to 3 inches (5-8 cm), torpedograss recovered "rapidly and vigorously" following initial biomass reduction after fire, with new growth sprouting from previously dormant buds [7]. After a May prescribed fire near East Lake Tohopekaliga, Florida, torpedograss sprouted "immediately" in areas that were burned or burned and disked. Rhizome biomass was reduced by 66% in burned areas and 93% in burned and disked areas 100 days after treatment but recovered to approximately 20% of pretreatment levels after 250 days in both treatments [92]. Two studies provide information on aboveground growth after wildfire in the Lake Okeechobee region. One month after an August wildfire, the average torpedograss height in burned areas was 4 to 8 inches (10-20 cm) compared to ≥30 inches (70 cm) in unburned areas [45]. Six weeks after top-kill from a February wildfire, torpedograss height averaged 8 inches (20 cm) [46].
In Florida, managers observed torpedograss mortality in areas exposed to unusual drought conditions, where water levels receded 2 to 3 feet (0.6-0.9 m) below the surface of the ground. Fire consumed both aboveground vegetation and the upper, dry, compacted peat layers to a depth of 3 to 4 inches (8-10 cm). Torpedograss mortality was also observed following a prescribed fire in 1990 and a wildfire in 1997; in both years, water levels were below the ground's surface [7]. However, dry conditions do not always result in torpedograss mortality. In 2007, torpedograss populations in marshes around Lake Okeechobee survived repeated fires during a record low-water period (personal communication [6]).
Flooding after fire may also lead to torpedograss mortality. One manager from Florida reported that he expected torpedograss populations to respond well and potentially expand following fire, depending on postfire water levels; he observed torpedograss mortality and a subsequent population decline in an area that experienced flooding for months following fire (personal communication [6]). In the Florida Everglades, torpedograss cover was significantly lower 1 year after a mixed-severity prescribed fire in areas flooded after treatment (P<0.001) [98]. See Fire Management Considerations for more information on this study.
Herbicide treatment following fire may reduce torpedograss populations. See Fire Management Considerations for more information.
Long-term impacts of fire on torpedograss have not been reported as of this writing (2011).
The limited information available (2011) suggests that torpedograss populations develop heavy fuel loads that may alter fire characteristics.
In Florida, torpedograss grows in dense stands and may comprise 80% of the biomass of an area where it establishes (personal communication [6]). Along the shores of Lake Kariba, Zimbabwe, the average standing crop biomass of torpedograss was 7,620 ± 21.8 kg/ha with an average moisture content of 72.91% ± 0.24 (sampled February to May) [16]. Dead leaves and culms of torpedograss accumulate in areas without grazing [79].
One manager from Florida believes that populations of torpedograss accumulate much more fuel than the native plant communities that it replaces, particularly in sawgrass (Cladium jamaicense) and spikerush prairies and American white waterlily sloughs. The increased biomass may lead to "hotter" fires resulting in higher mortality of native species, particularly sawgrass (personal communication [6]).
Torpedograss has been widely planted as forage for livestock and may have some nutritional value to wildlife.
Palatability and nutritional value: Torpedograss has been planted throughout the world as forage for domestic livestock [2,44,65,69,79]. A nonnative species guide reports that, though used for pasturage, torpedograss has relatively low nutritional value, protein content, and palatability compared to other grasses. Its advantage as a forage grass is that it is relatively palatable when young and can withstand heavy grazing and trampling [49]. It can be fed to cattle either green or as hay [31]. However, torpedograss was reported as poisonous to horses in Florida [92,109].
Torpedograss may have some value as food for wildlife. Populations of torpedograss near Lake Okeechobee supported a diverse arthropod and nematode fauna, and plants were not limited by invertebrate herbivory or damage [29]. In feeding trials in Florida, it was consumed by the nonnative channeled apple snail (Pomacea insularum) [4,5]. On the Mississippi River delta, both above- and belowground vegetation of torpedograss was eaten by snow geese and brants in the fall [72]. It was eaten by redbread tilapia (Tilapia rendalli) in Lake Kariba in Zimbabwe [16]. Seeds of torpedograss were found in fecal pellets of wild spur-thighed tortoises in Spain [26].
Cover value: No information is available on this topic.
Torpedograss occurs in both aquatic and terrestrial plant communities [44], including coastal sand, wetland, and forested plant communities.
Coastal sand plant communities: Torpedograss establishes in coastal sand plant communities around the Gulf of Mexico, including sand dunes [11,67,68,74,77,81], ridges [67], plains [11], and beaches [68]. Torpedograss occurred in coastal dune communities along the northern Gulf Coast including Texas, Mississippi, Louisiana and the west coast of Florida. Common associates included turtleweed (Batis maritima), saltgrass (Distichlis spicata), marsh fimbry (Fimbristylis castanea), largeleaf pennywort (Hydrocotyle bonariensis), and dwarf saltwort (Salicornia bigelovii) [77]. On a barrier island between the Mississippi Sound and the Gulf of Mexico, torpedograss occurred on sand dunes dominated by seaoats
(Uniola paniculata), moist dunes with Le Conte's flatsedge (Cyperus lecontei) and largeleaf pennywort, and in a coastal sand frostweed-woody goldenrod (Helianthemum arenicola-Chrysoma pauciflosculosa) plant community [81]. On an island off the coast of Louisiana, torpedograss established on sandy, compacted turf with erect centella (Centella erecta) and starrush whitetop (Rhynchospora colorata) [10]. Herbarium records from Texas documented torpedograss occurring between a seawall and saltgrass flats [36]. In coastal areas of Mexico, torpedograss occurred on sand dunes and sandy plains with slender grama (Bouteloua repens), sideoats grama (B.
curtipendula), Acapulco grass (B. dimorpha), bahiagrass (Paspalum notatum), hilograss (P. conjugatum), and mesosetum grasses (Mesosetum spp.) [11].
Wetlands and riparian areas: Torpedograss establishes in a variety of moist plant communities, including wetlands [13,17,18,30,35,36,76,80,84,113], wet prairies [24,33,34,61,73,113], and in or around water bodies [29,88,93,113].
Wetlands: In Gulf Coast freshwater marshes, torpedograss occurred with alligatorweed (Alternanthera philoxeroides), herb of grace (Bacopa monnieri), fragrant flatsedge (Cyperus odoratus), common water hyacinth (Eichhornia crassipes), spikerush (Eleocharis sp.), hydrocotyle (Hydrocotyle sp.), sprangletop
(Leptochloa sp.), maidencane (Panicum hemitomon), common reed (Phragmites
australis), bulltongue arrowhead (Sagittaria lancifolia ssp. media), saltmeadow cordgrass (Spartina patens), cattail (Typha sp.), hairypod cowpea
(Vigna repens), and giant cutgrass (Zizaniopsis miliacea) [30]. On a barrier island in the Gulf Islands National Seashore, Florida, torpedograss occurred in freshwater marshes with southern umbrella-sedge (Fuirena scirpoidea) and broomsedge bluestem (Andropogon virginicus) [76]. In Florida, torpedograss dominated part of a 1-year-old wetland constructed for wastewater treatment but 2 years later had been replaced by pickerelweed (Pontederia cordata), bulltongue arrowhead, and Olney's threesquare bulrush [13]. In southwestern peninsular Florida, torpedograss was
an occasional species in disturbed wet areas and seasonal ponds and sloughs occurring within dry prairies with saw-palmetto (Serenoa repens); in South Florida slash pine (Pinus elliottii var. densa) flatwoods; and in river-corridor hammocks with live oak (Quercus virginiana), laurel oak (Q. laurifolia), and cabbage palmetto (Sabal palmetto) [55].
On the Mississippi River delta, torpedograss occurred in coastal marsh plant communities containing mixtures of common reed [17,18,84], saltmeadow cordgrass [17], smooth cordgrass (S.
alterniflora), cattails (Typha spp.), Olney's threesquare bulrush (Schoenoplectus americanus), and giant cutgrass [84]. In the same region, torpedograss occurred on mud flats with giant cutgrass, seacoast bulrush (Bolboschoenus robustus), smooth cordgrass, and narrow-leaved cattail (Typha angustifolia) [72]. In southeastern Louisiana, torpedograss occurred in thick-mat floating-marsh plant communities. Species composition varied, but these communities contained
monocultures or mixtures of bulltongue arrowhead (Sagittaria lancifolia), cattails, Olney's threesquare bulrush, cordgrass (Spartina spp.), giant cutgrass, and common reed [80]. Herbarium records from Texas documented torpedograss occurring in a small freshwater marsh with spadeleaf
(Centella asiatica), jointed flatsedge (Cyperus articulatus), tapertip flatsedge
(C. acuminatus), velvet panicum (Dichanthelium scoparium), Virginia buttonweed
(Diodia virginiana), and mountain spikerush (Eleocharis montana) [36].
Wet prairies: In southeastern Florida, torpedograss occurred in wet prairies characterized by St. Johnswort (Hypericum spp.), yelloweyed grass (Xyris spp.), spadeleaf, rush (Juncus spp.), panicgrass (Panicum spp.), and Tracy's beaksedge
(Rhynchospora tracyi) [73]. Torpedograss occurred infrequently and at low cover in wet prairies in west-central Florida. Common species included dwarf crabgrass (Digitaria serotina), broadleaf carpetgrass (Axonopus compressus), knotgrass (Paspalum distichum), and pineland threeawn (Aristida stricta) [24]. In southwestern Louisiana, torpedograss occurred in plant communities of intermixed prairie and cheniere (ridges made of shell fragments and sand that rise above sea level in coastal marshes). Species commonly found in prairies included golden tickseed (Coreopsis tinctoria), rosy camphorweed (Pluchea rosea), blackeyed Susan (Rudbeckia hirta var.pulcherrima), marsh flatsedge (Cyperus pseudovegetus), keeled bulrush (Isolepis koilolepis), slickseed fuzzybean (Strophostyles leiosperma), tapertip rush (Juncus acuminatus), forked rush (J. dichotomus), gaping grass (Panicum hians), brownseed paspalum (Paspalum plicatulum), and prairie wedgescale (Sphenopholis obtusata). Common species on chenieres included live oak, sugarberry (Celtis laevigata), and Hercules' club
(Zanthoxylum clava-herculis) [34]. Torpedograss occurred in smooth cordgrass prairies along the Mississippi River delta [33] and in Louisiana and Texas [33,61].
In or around water bodies: In and around Lake Okeechobee in Florida, torpedograss established with Gulf Coast spikerush (Eleocharis cellulosa), American white waterlily (Nymphaea odorata) [93], and little sand cordgrass (Spartina bakeri) [29]. Herbarium records from Florida documented torpedograss occurring in and around a pond with Spanish needles (Bidens bipinnata), shortleaf spikesedge (Kyllinga brevifolia), taperleaf water horehound (Lycopus rubellus), and baldcypress (Taxodium distichum) [113]. Torpedograss occurred in a disturbed shoreline plant community in southeastern Alabama. The shoreline plant
community contained yellowfruit sedge (Carex annectens) and southern waxy sedge
(C. glaucescens). Woody species included wax-myrtle (Myrica cerifera) and black
tupelo (Nyssa sylvatica) [88].
Forested plant communities: Torpedograss establishes in some areas with a tree canopy. Herbarium records from Florida documented torpedograss occurring along a road in sand pine (Pinus clausa) scrub and in slightly disturbed areas in
white sand scrub associated with coastal plain honeycombhead (Balduina angustifolia), blue maidencane (Amphicarpum muhlenbergianum), lopsided Indiangrass (Sorghastrum secundum), jeweled blue-eyed grass (Sisyrinchium xerophyllum); in oak (Quercus) woods, and in pinelands with cabbage palmetto, serenoa (Serenoa), and sweetgale (Myrica) [113].
At the Cumberland Island National Seashore off the coast of southern Georgia, torpedograss was restricted to open areas along roads bisecting maritime hammocks and pine (Pinus)-oak forests. Live oak dominated maritime hammocks, while loblolly pine (Pinus taeda), slash pine (P.
elliottii), longleaf pine (P. palustris), and live oak occurred in pine-oak forest [116].
On a barrier island between the Mississippi Sound and the Gulf of Mexico, torpedograss occurred in open forests with slash pine, sand live oak (Q. geminata), and myrtle oak (Q. myrtifolia) [81]. Herbarium records from Texas documented torpedograss as common in a drainage ditch along the edge
of a patch of forest dominated by sugarberry and nonnative Chinese tallow
(Triadica sebifera)[36].
Panicum repens is a species of grass known by many common names, including torpedograss, creeping panic, panic rampant, couch panicum, wainaku grass, quack grass, dog-tooth grass, and bullet grass. Its exact native range is obscure. Sources suggest that the grass is native to "Africa and/or Asia",[1] "Europe or Australia",[2] "Eurasia",[3] "Australia",[4] "Europe, Asia, and Africa",[5] or other specific regions, including the Mediterranean, Israel, and Argentina.[6] It is present in many places as an introduced species and often a noxious weed. It has been called "one of the world's worst weeds."[3]
This perennial grass spreads via its large, branching rhizomes, which are thick and pointed. The pointed shape of the rhizome tip gives the plant the name torpedograss. The rhizomes creep along the ground or float in water, forming floating mats. They can reach a length of 6 m (20 ft) and a soil depth of 7 m (23 ft), and they can form a mat 15 cm (5.9 in) thick. The spreading rhizomes sprout repeatedly to form colonies of stems.[6] The stems are 20 to 90 cm (7.9 to 35.4 in) tall,[7] sometimes reaching 1 m (3 ft 3 in). They grow erect or bend down. The leaves are stiff and straight, linear in shape, and flat or folded. They are sometimes white in color and waxy in texture. The inflorescence is a loose panicle of branches bearing small spikelets 2 to 3 mm (0.079 to 0.118 in) long.[6][7]
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 South Florida and it easily escaped cultivation,[6] eventually becoming "one of the most serious weeds in Florida," spreading to more than 70% of the waterways in the state.[1] In Lake Okeechobee, it has invaded more than 16,000 acres of marsh.[6] It displaces native plants,[8] growing colonially in thick, monotypic stands.[3] Dense mats or stands of the grass cause hypoxia in the water.[6] Torpedograss management in flood-control systems costs an estimated US$2 million per year.[3]
The plant is established in sandy coastal habitat on the United States' Gulf Coast, such as beaches and dunes, from Florida to Texas, where it occurs with beach plants such as turtleweed (Batis maritima), saltgrass (Distichlis spicata), marsh fimbry (Fimbristylis castanea), largeleaf pennywort (Hydrocotyle bonariensis), and dwarf saltwort (Salicornia bigelovii). It grows on many barrier islands. It grows in many types of wetland habitat, in and out of the water. It grows in freshwater marshes, salt marshes, mud flats, wet prairies, tide pools, bogs, and lakesides. It also invades drier habitat, such as coastal pine forests and white sand scrub. It easily moves into disturbed and cultivated areas such as ditches and canals.[6] It is a nuisance in sod production.[1] In Hawaii, it is a weed of sugarcane (Saccharum officinarum).[3][5] In other areas, it can be found in turf and orchards.[5] In the Florida turfgrass industry, it is the second-worst weed known.[9] The grass can grow in a variety of habitats, but it does not tolerate cold and it is rarely found above subtropical latitudes or at altitude.[6]
The grass spreads primarily via its rhizome. It has been noted to grow 1.3 cm (0.51 in) in length per day. The stems and rhizomes also produce tillers. The rhizome can endure drying and flooding. Dry or wet conditions may reduce the number of shoots produced by the rhizome, but they do not kill it. The rhizome can disperse when parts of it break off and drop onto the substrate elsewhere, anchoring and putting up new shoots. The plant survives and sprouts after herbicide application, grazing, cutting, plowing or disking, and burning. The grass rarely reproduces by seed.[6] It has been noted to reproduce by seed in Portugal,[9] but does not do so in the United States,[10] and it was described as "incapable of fruiting" in Japan. Seeds are sometimes observed but they are apparently rarely viable, with many studies describing zero germination.[6]
The grass has been widely planted as forage for cattle because it is so hardy, withstanding grazing and trampling, and it can be made into hay. However, it is not one of the more palatable or nutritious grasses. It is also good for erosion control because it binds the soil. Indeed, it is still recommended for planting along shorelines to stabilize them.[11]
Torpedograss in a ditch Panicum repens is a species of grass known by many common names, including torpedograss, creeping panic, panic rampant, couch panicum, wainaku grass, quack grass, dog-tooth grass, and bullet grass. Its exact native range is obscure. Sources suggest that the grass is native to "Africa and/or Asia", "Europe or Australia", "Eurasia", "Australia", "Europe, Asia, and Africa", or other specific regions, including the Mediterranean, Israel, and Argentina. It is present in many places as an introduced species and often a noxious weed. It has been called "one of the world's worst weeds."
