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Cogongrass encroaching on a Florida upland pine forest. Photo courtesy of UF/IFAS.

Species Name: 
Imperata cylindricaL. Raeuschel

Common Name(s):
Cogongrass, Cogon Grass, Japgrass

Synonymy:
Imperata cylindrica (L.) Beauv.
Imperata brasiliensis Trinius (misapplied)

Species Description:
Cogongrass, Imperata cylindrica, is a perrenial, rhizomatous grass that is somewhat variable n appearance. The species puts out extensive rhizomes that give rise to 3-10' long spreading stems and the leaf blade bunches that grow out of the stems. The leaf blades begin at ground level and leaves typically range from 1-4 feet in length. Blades range from 1/2-3/4 inches in width, possess finely serrate sharp margins, a white, off-center mid-vein, and are hairy at the base. The finely serrate leaf margins contribute to the undesirable forage qualities of this grass. Young leaves are light green while older leaves are orange-brown to brown in color. The ligules (membranous or hairy appendages at the junction between sheath and blade) are brown and papery

This grass produces long, fluffy-white panicles (seedheads) (Langland and Burks 1998, MacDonald et al. 2006).

Potentially Misidentified Species:
General difficulties in grass species identification for the layperson notwithstanding, the Florida range of Imperata cylindrica overlaps with the range of another non-native congener, Brazilian satintail I. brasiliensis. These two species are morphologically and genetically very similar. Where they co-occur, they readily hybridize to yield hybrids capable of producing fertile offspring. Positive identification of the two species may require analysis of cytological, genetic and morphological attributes and some authorities consider the species to be synonymous (USDA FEIS).

II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
Cogongrass is native to southeast Asia, the Philippines, China, and Japan. This invasive plant that can now be found throughout tropical and subtropical regions on every continent except Antarctica. The species thrives in areas disturbed by human activities (MacDonald 2004).

Imperata cylindrica was accidentally as well as intentionally introduced to the United States in the first half of the 20th century. The species has since spread across the southeastern United States, extending from Florida to eastern Texas (Bennett 2006). I. cylindrica also extends northward to Virginia and Maryland along the east coast and into Oregon on the west coast (MacDonald et al. 2006, GBEP 2007). In Florida, ogongrass now occurs from the panhandle region well into south Florida.

IRL Distribution:
Imperata cylindrica can be found within the IRL watershed from Volusia County south through Martin County. The USDA Plants Database currently shows the species absent from the southernost portion of the watershed in palm Beach County, but indicates that the species is again present to the south in Miami-Dade County.

III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:

Abundance:
MacDonald et al. (2006) estimate that worldwide, cogongrass infests around 200,000 ha of agricultural land. In Florida, hundreds of hectares of reclaimed phosphate mining land have been invaded by Imperata cylindrica monocultures. Established cogongrass stands can produce more than a ton per hectare of rhizome biomass (MacDonald et al. 2006).

Reproduction:
Cogongrass reproduces both asexually through the production of clonal individuals sent up from new rhizomes and also through sexual flowering and seed production. Flowering occurs primarily in the spring and also in response to stress events such as burning or mowing. Flowering is highly variable among plants and between stands and ranges from none to frequent (Sajise 1972).

Cogongrass is monoecious (male and female reproductive organs on the same individual) and the flowers are complete (having a pair of female stamens and a pair of male stigma present in each flower), but the species is an obligate out-crosser.

The small seeds are attached to plumes of long hairlike projections to facilitate wind dispersal and as many as 3,000 seeds are produced per plant (FIPR 1997, FloriData).

Embryology:
Although large numbers of seeds may be produced by individual plants, only a small percentage of these successfully establish as seedlings, and obligate outcrossing leads to low overall spikelet fertilization success (Cavers 1983). Experimental evidence suggests that germination rates of fertilized caryopsis (the dry fruit, commonly called the grain) are high (> 90%), however.

The species is slow to establish from seed and seedlings have been observed to emerge from soil taken from cogongrass infested areas for up to three months following flowering. Natural recruitment of seedlings was observed in disturbed areas where survivorship beyond eight months was less than 20% but remained steady thereafter (FIPR 1997).

IV.  PHYSICAL TOLERANCES

Temperature:
Above-ground cogongrass biomass does not tolerate cool temperatures well and in warm temperate regions where the species occurs, the rhizome system usually remains dormant through the winter months (GBEP 2007). Rhizomes are susceptible to subfreezing temperatures, although Wilcut et al. (1988) reports survival of rhizome systems in Alabama despite winter temperatures of -14°C.

The optimum temperature for seed germination has been reported as 30°C (Dickens and Moore, 1974).

Hydrology:
Imperata cylindrica is commonly encountered along wetland margins, but it is intolerant of conditions of prolonged soil inundation by water (GBEP 2007).

Specialized anatomy of the rhizome mat allows for water conservation and cogongrass performs well on fine sand to heavy clay soils and in soils of low fertility (MacDonald et al. 2006).