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

Spanish: camalote

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; cultivated and naturalized elsewhere (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.
Philippines Philippine Islands	Philippine Islands	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized

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)	New South Wales	introduced invasive	National Herbarium of New South Wales (2013) A local cultivar (cv. 'Olive') has become naturalised and posing a threat to natural wetlands in the tropics and warm temperate areas.
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)
Central America Central America (Pacific rim)	Costa Rica (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	El Salvador (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Guatemala (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Honduras (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Nicaragua (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Central America Central America (Pacific rim)	Panama (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
China China	China (People's Republic of)		Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2013) Streams in shallow water, ricefields; below 1000 m. Hainan, Yunnan.
Indonesia Indonesia	Indonesia (Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 187)
Malaysia Malaysia	Malaysia (country of)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Singapore Singapore	Singapore (Republic of)	native	Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. (2009) (p. 50) Common
South America (Pacific rim) South America (Pacific rim)	Colombia	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
South America (Pacific rim) South America (Pacific rim)	Ecuador (Republic of) (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
South America (Pacific rim) South America (Pacific rim)	Perú (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Taiwan Taiwan Island	Taiwan Island		Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2013) Streams in shallow water, ricefields; below 1000 m.
Thailand Thailand	Thailand (Kingdom of)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized
Vietnam Vietnam	Vietnam (Socialist Republic of)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized

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 invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized

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).