Hymenachne amplexicaulis (Rudge) Nees, Poaceae

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Present on Pacific Islands?  no

Primarily a threat at high elevations?  no

Risk assessment results: 

Australia:  Reject, score: 21 (Go to the risk assessment)
Risk assessment from the Government of Queensland, Australia (PDF format).

Common name(s): [more details]

Chinese: mo fu cao

English: hymenachne, olive hymenachne, trompetilla, West Indian marsh grass

Habit:  grass

Description:  "Habit: Perennial. Culms decumbent; robust; 200-350 cm long; spongy; rooting from lower nodes. Culm-internodes solid. Culm-nodes glabrous. Leaf-sheaths glabrous on surface; outer margin glabrous, or hairy. Ligule an eciliate membrane; 1-2.5 mm long. Leaf-blade base amplexicaul. Leaf-blades lanceolate; 15-33 cm long; 12-28 mm wide. Leaf-blade surface glabrous. Leaf-blade margins scabrous; tuberculate-ciliate; hairy at base. Leaf-blade apex acuminate. Inflorescence: Inflorescence a panicle. Panicle spiciform; linear; 10-40 cm long; 1-2 cm wide. Spikelets solitary. Fertile spikelets pedicelled. Pedicels oblong. Fertile spikelets: Spikelets comprising 1 basal sterile florets; 1 fertile florets; without rhachilla extension. Spikelets lanceolate; dorsally compressed; acuminate; 3.5-5.5 mm long; falling entire. Glumes: Glumes dissimilar; shorter than spikelet; thinner than fertile lemma. Lower glume ovate; 1-1.7 mm long; 0.3 times length of spikelet; hyaline; without keels; 3 -veined. Lower glume apex cuspidate. Upper glume lanceolate; 2.8-3.9 mm long; 0.7-0.8 times length of spikelet; membranous; without keels; 5 -veined. Upper glume apex caudate; awned; 1-awned. Upper glume awn 0.5 mm long. Florets: Basal sterile florets barren; without significant palea. Lemma of lower sterile floret similar to upper glume; lanceolate; 3.6-4.6 mm long; 1 times length of spikelet; membranous; 5 -veined; caudate. Fertile lemma lanceolate; 2.5-3.5 mm long; cartilaginous; pallid; without keel; 3-veined. Lemma margins involute. Lemma apex acuminate. Palea separating from lemma above; involute; 1 times length of lemma; cartilaginous; 2-veined; without keels. Palea apex acuminate. Flower: Anthers 3; 1.1-1.2 mm long. Fruit: Caryopsis ellipsoid" (GrassBase).

Habitat/ecology:  "Swampy situations such as riverbanks and seasonally flooded areas in water up to 2 m deep.  It has the ability to smother native vegetation and form dense and extensive monospecific stands." (Smith, 2002; p. 74). Grows in water up to 2 m deep in periodically inundated wetlands. It does not grow in permanent water and requires alternating periods of flooding and dryness to establish and survive (Csurhes and Edwards, 1998; pp. 168-169).  "As a semi-aquatic grass, hymenachne thrives best on clay soils that are inundated during the wet season rains but dry out to some extent in the dry season. The subsoil must remain moist during the dry season, as hymenachne can only withstand short periods of drought. Consequently, it is found mainly in low-lying areas along the edges of permanent water. Hymenachne can withstand prolonged (40 weeks) flooding by growing above floodwaters. Because it grows so rapidly, it flourishes in wetlands that receive sediment and nutrient-rich water, and it may be a good indicator of such pollution. However, it does not tolerate brackish water and does not grow well in shaded areas"  (Australian Weed Management Guide).

Propagation:  Seed, dispersed by floodwater or in contaminated stock feed. Pieces of plants can also be carried to new locations by flood water. Promoted as a pasture grass. (Csurhes & Edwards, 1998; pp. 168-169).

Native range:  Mexico, Caribbean Islands, Central and South America (GRIN).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Papua New Guinea Papua New Guinea (eastern New Guinea Island)	Papua New Guinea (eastern New Guinea Island)		Henty, E. E. (1969) (p. 109) Widely spread, in shallow water at the margins of swamps and slow rivers, at low altitudes.

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	Northern Territory	introduced cultivated	Csurhes, S./Edwards, R. (1998) (pp. 168-169)
Australia Australia (continental)	Northern Territory	introduced invasive cultivated	Smith, Nicholas M. (2002) (p. 74) Spreading throughout the Adelaid and Mary River flood plains.
Australia Australia (continental)	Queensland	introduced invasive cultivated	Csurhes, S./Edwards, R. (1998) (pp. 168-169)
China China	China (People's Republic of)		Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2011) Streams in shallow water, ricefields; below 1000 m. Hainan, Yunnan.
Colombia Colombia	Colombia (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Costa Rica Costa Rica	Costa Rica (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Ecuador (Mainland) Ecuador	Ecuador (Republic of) (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
El Salvador El Salvador	El Salvador (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Guatemala Guatemala	Guatemala (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Honduras Honduras	Honduras (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Indonesia Indonesia	Indonesia (Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 187)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Nicaragua Nicaragua	Nicaragua (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Panama Panama	Panama (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Perú Perú	Perú (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Singapore Singapore	Singapore (Republic of)	native	Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. (2009) (p. 50) Common
Taiwan Taiwan	Taiwan Island		Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2011) Streams in shallow water, ricefields; below 1000 m.

Also reported from
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
United States (continental except west coast) United States (other states)	USA (Florida)	introduced	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2011)

Comments:  A "weed of national significance" in Australia. Has invaded tropical wetlands in Queensland.

Planting of this species is prohibited in Miami-Dade County, Florida (U.S.) (Miami-Dade County Dept. of Planning and Zoning, 2010).

Control:  "Established plants are difficult to control.  Scattered plants may be removed manually, all stolons and roots must be removed to prevent regrowth.  Larger patches can be treated with herbicides approved for use in aquatic environments"  (Weber, 2003; p. 206).

Additional information:
Photos and additional information at University of Florida, Center for Aquatic and Invasive Plants (see thumbnails above).
Weed Management Guide produced by the CRC for Australian Weed Management. (PDF format).
Information from the book "Identification and biology of non-native plants in Florida's natural areas" (PDF format).
Fact sheet from the Government of Queensland, Australia. (PDF format).

Additional online information about Hymenachne amplexicaulis is available from the Hawaiian Ecosystems at Risk project (HEAR).

Information about Hymenachne amplexicaulis as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

Taxonomic information about Hymenachne amplexicaulis may be available from the Germplasm Resources Information Network (GRIN).

References:

Adams, C. D. 1972. Flowering plants of Jamaica. University of the West Indies, Mona, Jamaica. 848 pp.

Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. 2009. A checklist of the total vascular plant flora of Singapore: native, naturalised and cultivated species. Raffles Museum of Biodiversity Research, National University of Singapore. 273 pp.

Clayton, W. D./Harman, K. T./Williamson, H. 2002. World Grass Species: Descriptions, Identification, and Information Retrieval (online resource).

Csurhes, S./Edwards, R. 1998. Potential environmental weeds in Australia: Candidate species for preventative control. Canberra, Australia. Biodiversity Group, Environment Australia. 208 pp.

Henty, E. E. 1969. A manual of the grasses of New Guinea. Department of Forests, Division of Botany, Botany Bull. No. 1. Lae, New Guinea. 215 pp.

Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. 1979. A geographical atlas of world weeds. John Wiley & Sons, New York. 391 pp.

Langeland, K. A./Burks, K. Craddock. eds. 1998. Identification and biology of non-native plants in Florida's natural areas. Gainesville, FL: University of Florida. 165 pp.

Miami-Dade County Dept. of Planning and Zoning. 2010. The landscape manual. Draft ninth edition, August 2010. 249 pp.

Smith, Nicholas M. 2002. Weeds of the wet/dry tropics of Australia - a field guide. Environment Centre NT, Inc. 112 pp.

U.S. Dept. Agr., Agr. Res. Serv. 2011. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.

U.S. Dept. Agr., Nat. Res. Cons. Serv. 2011. The PLANTS Database. National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

Weber, Ewald. 2003. Invasive plants of the World. CABI Publishing, CAB International, Wallingford, UK. 548 pp.

Zhengyi, Wu/Raven, Peter H./Deyuan, Hong. 2011. Flora of China (online resource).