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Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

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FACT SHEET: WEST INDIAN MARSH GRASS

West Indian Marsh Grass 

Hymenachne amplexicaulis (Rudge) Nees 

Grass family (Poaceae)

NATIVE RANGE 

Tropical America and the West Indies 

DESCRIPTION 

West Indian marsh grass (Hymenachne amplexicaulis), also known as 

trompetilla, is a perennial grass adapted to wetland habitats. It is the only 

species in the genus Hymenachne that is present in Florida. The stem, in 

grasses called a culm, is glabrous (hairless), erect, up to six feet tall and filled 

with a white pith or aerenchyma. In aquatic plants, aerenchyma allows the 

easy movement of oxygen from the leaves to the roots. Stems that are 

submerged quickly produce roots from nodes and anchor to the wetland floor. 

The panicles are narrow, spike-like, cylindrical, 4-15 inches long and 0.4 

inches wide. Leaf blades are 4-16 in. long, and up to 11⁄2 inches wide, mostly 

hairless, heart-shaped at the base with earlike appendages and clasp around 

the stem. 

NOTE: West Indian marsh grass may be confused with the native grass 

American cupscale (Sacciolepis striata) and some other native grasses, but 

the presence of the white pith rules out many grass species as well as the 

earlike appendages at the leaf bases of West Indian marsh grass. 

ECOLOGICAL THREAT 

In Florida, diverse aquatic wetlands are habitats for feeding, resting, refuge 

and reproduction for wading birds, wood storks, snail kites, killifishes, live 

bearers, juvenile sunfishes, southern leopard frogs, pig frogs, green tree frogs, American alligators and American 

crocodiles, among other species of wildlife. 

West Indian marsh grass forms monotypic stands that create large amounts of biomass deposited in the aquatic habitat. 

Researchers are collecting evidence to suggest that wetland invasion of marsh grass causes changes to the biological 

diversity of the site, including reductions in native plants and animals, changes to water quality associated with plant 

community metabolism, flow regimes and possible exacerbation of flooding. Additionally, West Indian marsh grass may 

smother river banks and change plant recruitment, nutrient recycling and survival of riparian forest. 

DISTRIBUTION IN THE UNITED STATES 

West Indian marsh grass is present in central and south Florida where it has 

been found in at least twelve counties and also occurs in nearby Puerto Rico. It 

is not currently reported to occur in any other states in the U.S. 

HABITAT IN THE UNITED STATES 

West Indian marsh grass invades freshwater wetlands, flood plains and river 

banks. Field observations in Florida indicate that the plant grows vigorously in 

wetlands that are flooded by rivers containing nutrient runoff. Sites include 

shallow ponds, in or along streams, in ditches, swamps, marshes, wet 

disturbed sites such as wet pastures, drainage canals, river banks, and 

cypress swamps. It also may be found floating. When grown in a nutrient rich wetland, mature plants are robust and form 

extensive colonies by producing cord-like stolons that extend many feet underwater. 
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Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

http://www.nps.gov/plants/alien/

BACKGROUND 

West Indian marsh grass is believed to have been introduced into Florida more 

than thirty years ago. Herbarium specimens indicate that the first report of the 

plant in Florida was in a ponded pasture in Palm Beach Co. West Indian marsh 

grass is used as forage in the neotropics, especially in Venezuela, Mexico and 

Cuba. Whether this introduction was intentional or not has not been 

determined. 

BIOLOGY & SPREAD 

In Florida, flowering of West Indian marsh grass occurs from September 

through December and plants typically produce one panicle but occasionally 

up to three in a consecutive manner. West Indian marsh grass grows from 

stolons which can become fragmented and carried great distances 

downstream by flowing water. It can also be spread by seed which has high viability and is produced in abundance. In 

Myakka State Park, West Indian marsh grass is thought to be spread by vehicles. West Indian marsh grass first observed 

along roads eventually moves into adjacent wetlands, probably by stolons or seeds in mud that stick to tires and 

equipment. If West Indian marsh grass invades reservoirs, additional spread of seeds and stolons can occur via 

secondary canals. Observations in marshes near Sarasota suggest that when subject to flooding, West Indian marsh 

grass is capable of very rapid stem elongation, increase in foliage volume and rapid nodal adventitious root production 

allowing emergent leaves to function at full photosynthetic capacity. Migratory birds may have carried seeds from nearby 

islands. 

MANAGEMENT OPTIONS 

The best approach to managing West Indian marsh grass in uninfested areas is 

to prevent its introduction. Once introduced, the appropriate method of control 

must be considered on a case-by-case basis, depending on the site conditions 

and level of infestation. Several control methods are available and an integrated 

pest management approach is recommended. Park rangers and the South 

Florida Water Management District have used registered systemic herbicides to 

control marsh grass by killing the buried stolons. Plant managers in Australia 

have used mechanical harvesters and solarization to kill small outbreaks of West 

Indian marsh grass. For assistance with determining the best strategy for your 

situation, please contact the experts listed below. 

Biological 

A potential biocontrol agent is being investigated for future use in management of in 

management of Hymenachne. It is an insect in the true bug family Blissidae (Order 

Hemiptera) and is known only by its Latin name Ischnodemus variegatus. It was first 

collected in 2000 in Florida on West Indian marsh grass and has a distinctive black and 

white color pattern on its wings. This insect is native to South America where it has 

been reported feeding on the West Indian marsh grass. Researchers observed that 

feeding damage of I. variegatus reduced the photosynthetic capacity and growth rate of 

West Indian marsh grass under greenhouse conditions. Field sampling has shown that 

I. variegatus is distributed across central and south Florida and large infestations 

produce severe seasonal damage to West Indian marsh grass. 

USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all 

recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use 

requirements, restrictions or recommendations. 

NOTICE: mention of pesticide products on this page does not constitute endorsement of any material.
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Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

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CONTACTS 

For more information on the management of West Indian Marsh Grass, please contact: 

• Rodrigo Diaz, Biological Control Research and Containment Laboratory, University of Florida, Fort Pierce, FL, 

rrdg at ufl.edu 

• Bill Overholt, Biological Control Research and Containment Laboratory, University of Florida, Fort Pierce, FL, 

waoverholt at mail.ifas.ufl.edu 

• Florida Department of Environmental Protection, 3900 Commonwealth Boulevard M.S. 49, Tallahassee, FL 

32399; 850-245-2118 (phone); http://www.dep.state.fl.us/ 

• Southwest Florida Water Management District. http://www.swfwmd.state.fl.us/ 

SUGGESTED ALTERNATIVE PLANTS 

Plant communities in Florida wetlands are composed of many native species like maidencane (Panicum hemitomon), a 

native grass that has been displaced by West Indian Marsh Grass. Other native wetland plants include pickerelweed 

(Pontederia cordata), arrowhead (Sagittaria lancifolia), saw-grass (Cladium jamaicense) and water lilies (Nymphaea 

odorata). For a complete list of native wetland plants in Florida, please visit this website: 

http://aquat1.ifas.ufl.edu/photos.html 

OTHER LINKS 

• Pacific Islands Ecosystems at Risk (PIER) http://www.hear.org/pier/species/hymenachne_amplexicaulis.htm 

• Queensland Government-Department of Natural Resources and Mines 

http://www.nrm.qld.gov.au/pests/psas/pdfs/Hymenachne.pdf 

• United States Department of Agriculture- Natural Resource Conservation Service 

http://plants.usda.gov/cgi_bin/topics.cgi?earl=plant_profile.cgi&symbol=HYAM2 

• Range Cattle Research and Education Center, University of Florida, Ona, FL http://weedext.ifas.ufl.edu/ 

AUTHORS 

Rodrigo Diaz and Bill Overholt, Biological Control Research and Containment Laboratory, University of Florida, Fort 

Pierce, FL 

EDITOR

Jil M. Swearingen, National Park Service, Center for Urban Ecology, Washington, DC

REVIEWERS 

Paula Benshoff, Myakka River State Park, Sarasota, FL 

Paul Pratt, U.S. Department of Agriculture, Agricultural Research Service, Ft. Lauderdale, FL 

PHOTOGRAPHS 

Rodrigo Diaz, Biological Control Research and Containment Laboratory, University of Florida, Fort Pierce, FL

REFERENCES 

Brambila, J. and F.J. Santana. 2004. First Records for Ischnodemus variegates (Hemiptera: Blissidae) in North 

America.Florida Entomologist 87:4. http://www.fcla.edu/FlaEnt/fe87p585.pdf

Hill, K.U. 1996. Hymenachne amplexicaulis: a review of the literature and summary of work in Florida. 

http://www.naples.net/~kuh/hymen.htm. 

Csurhes, S.M., Mackey, A. P. and L. Fitzsimons. 1999. Hymenachne in Queensland. Pest Status Review Series. 

Queensland Government-Natural Resources and Mines. http://www.nrm.qld.gov.au/ 

Diaz, R. Overholt, W. and J. P. Cuda. Exotics in the Wetlands: West Indian Marsh Grass. 

http://edis.ifas.ufl.edu/pdffiles/IN/IN49100.pdf 

Houston, W. A. and L. J. Duivenvoorden. 2002. Replacement of littoral native vegetation with the ponded pasture grass 

Hymenachne amplexicaulis: effects on plant, macroinvertebrate and fish biodiversity in the Fitzroy River, Central 

Queensland, Australia. Marine and Freshwater Research 53:1235-1244. 
16 June 2006 Page 4 of 4 

Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

http://www.nps.gov/plants/alien/

Langeland, K. A. and K. Craddock Burks (eds.) 1998. Identification and Biology of Non-native Plants in Florida’s Native 

Areas. University of Florida, Gainesville, Florida, USA. 

Overholt, W. A., S. M. L. Ewe, R. Diaz, E. C. Morgan and O. E. Moeri. 2004. Feeding effects of Ischnodemus variegatus

(Hemiptera: Blissidae) on photosynthesis and growth of Hymenachne amplexicaulis (Poaceae). Florida 

Entomologist 87: 312-316. 

Swearingen, J. 2009. WeedUS Database of Plants Invading Natural Areas in the United States: West Indian Marsh Grass 

(Hymenachne amplexicaulis). http://www.invasive.org/weedus/subject.html?sub=5733. 

USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 

70874-4490 USA.