Hymenachne amplexicaulis (Rudge) Nees, Poaceae

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Present on Pacific Islands?  no

Threat only at high elevations?  no

Risk assessment results:  Reject, score: 21 (Go to the risk assessment)

Common name(s): [more details]

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

Habit:  grass

Description:  "A robust, rhizomatous perennial grass to 1.6 m high which spreads on dry land and floats in water.  Stems erect or ascending from a prostrate base.  Leaf blades 10-45 cm long, 3-6 cm wide, strongly clasping the stem at the base with prominent light colored veins and hairy margins.  Flower heads spike-like, cylindrical, 20-40 cm long, sometimes few branched" (Smith, 2002; p. 74).

Culms usually trailing, 1 m or more long; leaf-blades 20-35 cm long, 2-3 cm broad, cordate-clasping; panicles 20-50 cm long, about 8 mm broad; spikelets 3-4 mm long, acuminate"  (Adams, 1972; p. 394).

"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" (World Grass Species).

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).

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:  Central and tropical America.

Presence:

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)
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. (2007)

Comments:  A noxious weed in Australia. Has invaded tropical wetlands in Queensland.

Additional information:  Photos and additional information at University of Florida, Center for Aquatic and Invasive Plants (see thumbnails above).

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

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.

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.

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.

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. 2007. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.