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Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Hymenachne amplexicaulis
(hymenachne)

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Datasheet

Hymenachne amplexicaulis (hymenachne)

Summary

  • Last modified
  • 16 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Hymenachne amplexicaulis
  • Preferred Common Name
  • hymenachne
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Monocotyledonae
  • Summary of Invasiveness
  • H. amplexicaulis is a perennial, stoloniferous, freshwater grass that forms monospecific stands in seasonally flooded environments of tropical, subtropical, and warm temperate climates. It is native to Central...

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Pictures

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PictureTitleCaptionCopyright
Hymenachne amplexicaulis (west indian marsh grass); thick, spike-like, panicles have basal branches held strictly erect.
TitlePanicles
CaptionHymenachne amplexicaulis (west indian marsh grass); thick, spike-like, panicles have basal branches held strictly erect.
Copyright©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); thick, spike-like, panicles have basal branches held strictly erect.
PaniclesHymenachne amplexicaulis (west indian marsh grass); thick, spike-like, panicles have basal branches held strictly erect.©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); aquatic plants produce upright, emergent culms from submersed, rooting stolons.
TitleShape and form
CaptionHymenachne amplexicaulis (west indian marsh grass); aquatic plants produce upright, emergent culms from submersed, rooting stolons.
Copyright©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); aquatic plants produce upright, emergent culms from submersed, rooting stolons.
Shape and formHymenachne amplexicaulis (west indian marsh grass); aquatic plants produce upright, emergent culms from submersed, rooting stolons.©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); upper leaves of emergent stems appear flat and triangular in silhouette.
TitleShape and form
CaptionHymenachne amplexicaulis (west indian marsh grass); upper leaves of emergent stems appear flat and triangular in silhouette.
Copyright©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); upper leaves of emergent stems appear flat and triangular in silhouette.
Shape and formHymenachne amplexicaulis (west indian marsh grass); upper leaves of emergent stems appear flat and triangular in silhouette.©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); stem-clasping leaf base with long, ciliate hairs along the margin of the clasping lobe.
TitleLeaf base
CaptionHymenachne amplexicaulis (west indian marsh grass); stem-clasping leaf base with long, ciliate hairs along the margin of the clasping lobe.
Copyright©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); stem-clasping leaf base with long, ciliate hairs along the margin of the clasping lobe.
Leaf baseHymenachne amplexicaulis (west indian marsh grass); stem-clasping leaf base with long, ciliate hairs along the margin of the clasping lobe.©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); stem-clasping leaf base with long, ciliate hairs along the margin of the clasping lobe.
TitleLeaf base
CaptionHymenachne amplexicaulis (west indian marsh grass); stem-clasping leaf base with long, ciliate hairs along the margin of the clasping lobe.
Copyright©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); stem-clasping leaf base with long, ciliate hairs along the margin of the clasping lobe.
Leaf baseHymenachne amplexicaulis (west indian marsh grass); stem-clasping leaf base with long, ciliate hairs along the margin of the clasping lobe.©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); mature spikelets, disarticulated below the glumes.
TitleMature spikelets
CaptionHymenachne amplexicaulis (west indian marsh grass); mature spikelets, disarticulated below the glumes.
Copyright©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); mature spikelets, disarticulated below the glumes.
Mature spikeletsHymenachne amplexicaulis (west indian marsh grass); mature spikelets, disarticulated below the glumes.©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); lanceolate spikelets appear awned, due to the gradually tapering tip of the lower lemma.
TitleSpikelets
CaptionHymenachne amplexicaulis (west indian marsh grass); lanceolate spikelets appear awned, due to the gradually tapering tip of the lower lemma.
Copyright©Colette C. Jacono-2010
Hymenachne amplexicaulis (west indian marsh grass); lanceolate spikelets appear awned, due to the gradually tapering tip of the lower lemma.
SpikeletsHymenachne amplexicaulis (west indian marsh grass); lanceolate spikelets appear awned, due to the gradually tapering tip of the lower lemma.©Colette C. Jacono-2010

Identity

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Preferred Scientific Name

  • Hymenachne amplexicaulis (Rudge) Nees

Preferred Common Name

  • hymenachne

Other Scientific Names

  • Agrostis monostachya Poir.
  • Hymenachne acutigluma (Steud.) Gilliland
  • Hymenachne gouinii E.Fourn.
  • Hymenachne pseudointerrupta C.Muell.
  • Panicum acutiglume Steud.
  • Panicum amplexicaule Rudge
  • Panicum amplexicaule var. deflexa Doll
  • Panicum amplexicaule var. erecta Doll
  • Panicum grisebachianum Mez
  • Panicum hasskarlii Steud. ex Zoll.
  • Panicum hymenachne Desv.
  • Panicum myurum G.Mey.

International Common Names

  • English: bamboo grass; dal grass; dhal grass; olive hymenachne; trumpet grass; water straw grass; West Indian marsh grass
  • Spanish: camalote; Hierba Lancha; trompetilla

Local Common Names

  • Bolivia: cañuela blanca; carrizo chico
  • China: mo fu cao
  • Colombia: canutillo; trompetilla
  • India: bamboo grass; dal grass
  • Paraguay: chingolo
  • Portugal: capim-capivara
  • Suriname: bamboegras

Summary of Invasiveness

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H. amplexicaulis is a perennial, stoloniferous, freshwater grass that forms monospecific stands in seasonally flooded environments of tropical, subtropical, and warm temperate climates. It is native to Central and South America, where populations have increased around human disturbance. H. amplexicaulis has been introduced to the USA and Australia, where both countries first observed its invasive abilities in the 1990s. Robust, long lived, tolerant to hydrological fluctuation, and able to spread locally by fragments and across distances by seed, H. amplexicaulis is capable of displacing native species and altering indigenous communities under natural regimes. It is known to hinder irrigation, drainage and hydroelectric systems in agricultural and urbanized systems. It has also corrupted indigenous genotypes by hybridizing with a native Australian congener to form the morphologically intermediate hybrid H. x calamitosaH. amplexicaulis was ranked by the Florida Exotic Pest Plant Council as a Category I invasive due to the ecological damage it has caused. In Australia, it is prohibited as a Class 2 Declared Pest and named a Weed of National Significance for its proven potential to invade wet areas across a wide geographic range.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Monocotyledonae
  •                     Order: Cyperales
  •                         Family: Poaceae
  •                             Genus: Hymenachne
  •                                 Species: Hymenachne amplexicaulis

Notes on Taxonomy and Nomenclature

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The genus Hymenachne P. Beauv. was established in 1812 and now contains eight to ten perennial grass species, distributed in the tropics and subtropics of the Americas, Australia and Asia. Diagnostic features of the genus include its aquatic habit and lower internodes filled with spongy aerenchyma, the cylindrical inflorescence, the margins of the upper lemma being flat, and the glumes not saccate (Webster, 1987). In Australia, the genus is ultimately characterized from other Panicae by the lower glume which encircles the spikelet base (Webster, 1987).

Hymenachne amplexicaulis is a distinct species native only to the neo-tropics of Central and South America (USDA ARS, 2014). However, taxonomic confusion persists in China, Taiwan, India, Indo-China, Malaysia, Papua New Guinea and even Australia, where the name Hamplexicaulis has regularly been misapplied to H. pseudointerrupta C. Muell. and to H. acutigluma (Steudel) Gilliland (Flora of China, 2006; Clayton et al., 2014). For example, current online images of true H. acutigluma specimens collected 1932 and 1954 from Queensland, Australia have been labelled in error as Hymenachne amplexicaulis (Kew Herbarium Catalogue, 2014). Similar misapplications apply to many collections from tropical Asia, such as early 1860s specimens of H. pseudointerrupta from Malacca, Malaysia, that as recently as 2002 were incorrectly annotated as lectotypes of H. amplexicaulis (Kew Herbarium Catalogue, 2014), and a 1915 collection from Luzon Province, Philippines, that was also annotated in error as H. amplexicaulis (Kew Herbarium Catalogue, 2014). A very early (1837) collection of H. pseudointerrupta from the Gangetic plain of interior India, also incorrectly determined as H. amplexicaulis in 2002 (Kew Herbarium Catalogue, 2014), demonstrates the wide geographic region where current taxonomic is misapplied.

Description

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Primarily from Clayton et al. (2014) and Cowie et al. (2000), with minor additions from Florida collections:

Habit

Perennial. Culms decumbent, few branched; robust; 200-350 cm long; 1 cm thick; spongy; rooting from lower nodes. Culm internodes solid. Culm nodes glabrous. Leaf-sheaths glabrous or with hairs on upper surface, outer margin glabrous or with hairs. Ligule a membrane 1-2.5 mm long, or absent. Leaf-blade base lobed and clasping. Leaf-blades flat, lanceolate or linear-triangular; 15-40 cm long; 12-30(60) mm wide. Leaf-blade surface glabrous. Leaf-blade margins scabrous; tuberculate-ciliate; basal margins long-ciliate. Leaf-blade apex acuminate gradually narrowed from the base. 

Inflorescence

Inflorescence a spike-like panicle. Panicle densely flowered; cylindrical; 10-40 cm long; 1-3 cm wide. The lower branches often distant; erect.

Spikelets

Fertile spikelets pedicelled, pedicels oblong.  Disarticulation below the first glume

Fertile spikelets

Spikelets comprising 1 basal sterile florets; 1 fertile florets; without rhachilla extension. Spikelets lanceolate, gradually narrowing to a long point; dorsally compressed; acuminate; (0.5)3-5.5 mm long.

Glumes

Glumes dissimilar; shorter than spikelet; thinner than fertile lemma. Lower glume ovate; 1-1.7 mm long; 0.3 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 length of spikelet; membranous; without keels; 5-veined, veins scabrous. 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 length of spikelet; membranous; 5-veined, veins scabrous; caudate. Fertile lemma lanceolate; 2.5-3.5 mm long; cartilaginous; pallid; without keel; 3-veined. Lemma margins involute. Lemma apex long-acuminate. Palea separating from lemma above; involute; 1 length of lemma; cartilaginous; 2-veined; without keels. Palea apex acuminate.

Flower

Anthers 3; 1.1-1.2 mm long.

Fruit

Caryopsis ellipsoid.

Plant Type

Top of page Grass / sedge
Herbaceous
Perennial
Seed propagated
Vegetatively propagated

Distribution

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Native distribution

H. amplexicaulis is naturally distributed in the Caribbean, central Mexico and Central America, and South America, south to Bolivia, Paraguay, northern Argentina and Uruguay. Native communities remain especially common along the Pacific and Atlantic coastal zones of the neo-tropics at low elevations up to 500 m above sea level. The occurrence of unusually high elevation populations, 1000-1500 m above sea level in the Andes chain of Ecuador and Peru (Flora del Conosur, 2014), and up to 2500-3000 m above sea level in mountain cloud forests of Venezuela (Missouri Botanical Garden, 2014), represent a smaller subset of South American collections.

Introduced distribution

USA    

H. amplexicaulis is known only from the extreme south-southeastern states of Florida and Lousiana. In Florida, 20 counties (out of 67) have been documented with herbarium specimens (FLAS; USF; LSU) representing floodplain marshes and the margins of hardwood swamps of the typically expansive and low elevation river basins of central and south central Florida.

Australia

H. amplexicaulis is widely distributed in Queensland and Northern Territory. In 2012 it was found in a restricted area of the northern coastal region of New South Wales (Australian Weeds Committee, 2012; Council of Heads of Australasian Herbaria, 2014).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

North America

MexicoWidespreadNative Not invasive Pohl, 1994; Kew Herbarium Catalogue, 2014States of Sinaloa, Tamaulipas; Campeche, Chiapas, Colima, Guerrero, Jalisco, Michocan (Huetamo), Nayarit, Oaxaca, Tabasco, Veracruz, Atlantic & Pacific zones
USAPresentPresent based on regional distribution.
-FloridaWidespread1957Introduced Invasive Wunderlin and Hansen, 2014Documented in 19 countries of the south central Florida peninsula. North Florida occurrence eradicated
-LouisianaLocalised2014Introduced2013 Invasive Urbatsch and Saichuk, 2014Vermilion Parish: drainage canals and abandoned rice field near town of Gueydan

Central America and Caribbean

BarbadosPresentNative Not invasive USDA-ARS, 2014
BelizePresentNative Not invasive Zuloaga et al., 2003
Costa RicaPresent1974Native Not invasive Field Museum, 2014Prov. Limon: Barro de Colorado Sur and sandbar in Rio Colorado
CubaPresentNative Not invasive USDA-ARS, 2014
DominicaPresentNative Not invasive USDA-ARS, 2014
Dominican RepublicPresent1985Native Not invasive FLAS, 2014Laguna Los Cimarrones, N of Guerra
El SalvadorPresentNative Not invasive Zuloaga et al., 2003Recent year
GuadeloupePresentNative Not invasive USDA-ARS, 2014Recent year
HaitiPresentNative Not invasive USDA-ARS, 2014Recent year
HondurasZuloaga et al., 2003
JamaicaPresentNative Not invasive USDA-ARS, 2014Recent year
MartiniquePresentNative Not invasive USDA-ARS, 2014Recent year
Netherlands AntillesWidespreadNative Not invasive Missouri Botanical Garden, 2014
NicaraguaWidespreadNative Not invasive Missouri Botanical Garden, 2014Pacific, Atlantic and Southern zones
PanamaWidespreadNative Not invasive Missouri Botanical Garden, 2014Barro colorado Island, Darien, Aquadulche, Canal zone. Recent year
Puerto RicoPresentNative Not invasive USDA-ARS, 2014

South America

ArgentinaWidespreadNative Not invasive Flora del Conosur, 2014Buenos Aires, Chaco, Corrientes, Distrito Federal, Entre Rios, Formosa, Missones, Salta, Santa Fe
BoliviaWidespreadNative Not invasive Missouri Botanical Garden, 2014La Paz, Pando, Santa Cruz, Beni, Cochabamba
BrazilWidespread2013Native Not invasive Zuloaga et al., 2003
-Minas GeraisWidespread2014Native Not invasive Pitelli et al., 2014Aimorés Reservoir, weedy
-ParanaLocalisedNative Not invasive Flora del Conosur, 2014
ColombiaWidespread1986Native Not invasive Missouri Botanical Garden, 2014Antioquia (edge of swamp); cordoba
EcuadorWidespread1990Native Not invasive Missouri Botanical Garden, 2014Coastal, Andean and Amazonian regions in the Provinces of Bolivar, Esmeraldas, Guayas, Los Rios (Jauneche Forest), Manabi, Napo, Pastaza, Sucumbios
French GuianaPresentNative Not invasive Zuloaga et al., 2003
GuyanaPresentNative Not invasive Zuloaga et al., 2003
ParaguayWidespread1994Native Not invasive FLAS, 2014; Flora del Conosur, 2014Alto Parana, Alto Paraguay, Amambay, Caaguazu, Caazapa, Central Concepcion, Cordillera, Guaira, Itapua, Neembucu, Paraguari, Presidente Hayes, San Pedro
PeruWidespreadNative Not invasive Tovar, 1981Depts. Huanuco, Loreto, Madre de Dios, Puno, San Martin in regions of Amazonia and Andes I.
SurinameLocalisedNative Not invasive Zuloaga et al., 2003
UruguayLocalisedNative Not invasive Flora del Conosur, 2014Montevideo
VenezuelaPresent1981NativeFLAS, 2014; FLAS, 2014Apure

Oceania

AustraliaWidespread2012Introducedplanted 1973, naturalised 1995 Invasive Broue, 1973; Council of Heads of Australasian Herbaria, 2014Coastal zones of Queensland, the Northern Territory and New South Wales
-Australian Northern TerritoryWidespread2012Introduced2000 Naturalised Invasive Council of Heads of Australasian Herbaria, 2014North western coastal zones of Darwin and Gulf districts including Wulagi, Marrara, Howard Springs, Fogg Dam, Harrison Dam and other nearby conservation areas
-New South WalesLocalised2012Introduced2012 naturalised Invasive Council of Heads of Australasian Herbaria, 2014Coastal zone in region between Casino, Grafton and Yuraygir National Park
-QueenslandWidespread2012Introduced1973 planted, 1995 naturalised Invasive Broue, 1973; Council of Heads of Australasian Herbaria, 2014Entire eastern coastline from Cape York, south to Brisbane and in the interior just west of Emerald

History of Introduction and Spread

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USA

The method by which H. amplexicaulis was introduced to the USA is not clear, although it is more likely to have been intentionally introduced as a pasture grass rather than accidentally or naturally introduced via migrating waterfowl (Langeland et al., 2008; Montemayor et al., 2013; Urbatsch and Saichuk, 2014).

H.amplexicaulis was first collected in the USA in 1957 in pasture in Florida’s southeastern peninsula. Twenty five years passed before a second location was documented in 1982, in an agricultural area approximately 60 km west of the first. By the 1990s, however, spread was notably expanding to new counties and associated problems were being reported, initially in ditches and ponds of the sugarcane growing regions south of Lake Okeechobee, then in the canals, creeks and bays westward (Langeland et al., 2008).

In the 2000s invasions become common in sloughs and marshes draining areas of southwestern Gulf coast and moved northward to riparian marshes of the Prairie/Shell Creek and Myakka River basins. Since the mid-2000s this species has spread to headwater marshes of the St. Johns River, most notably along airboat trails (Wunderlin and Hansen, 2014) and to the headwater marshes and shallow lakes of the Kissimmee River, located 50 km south of Orlando. As of the latest collection in 2013 [Chicone 1167 (USF); Jacono 899 (FLAS)] H. amplexicaulis continues to expand to new river basins within southcentral Florida.

A distant occurrence in the USA was located in Florida nearly 400 km north of the south central region and just west of the state capital, Tallahassee. Plants were found in 2009 at an approximately 2 hectare storm water pond [Anderson 24745 (FSU)] and were eradicated with herbicides within the year (G. Jubinski, pers. comm., 2010; repeat surveys confirmed the eradication (L. Anderson, pers. obs., 2012 and 2014). While it may be the only population to have been successfully extirpated in Florida, the management action negated the opportunity to assess its ability of the species to persist in Florida’s more temperate, northern climate.

H.amplexicaulis was first recorded in Louisiana in November 2013, in the low elevation, rice-growing region of Vermilion Parish. Plants that were found growing as sporadic clumps on the banks of irrigation and drainage canals have not only endured herbicide treatment and a cold winter, but have expanded along the canal banks (Urbatsch and Saichuk 2014; J. Saichuk, pers. comm., 2014). New populations have meanwhile appeared within the highly constructed rice growing area, one outside of cultivation, in an abandoned field converting to marsh (J. Saichuk, pers. comm., Dec. 2014). The Louisiana occurrence at 30° 59’ N latitude represents the northern extent of H. amplexicaulis populations worldwide.

Australia

H. amplexicaulis is widely distributed in Queensland and Northern Territory within the waterways and wetlands of the coastal and subcoastal zones. H. amplexicaulis was purposefully introduced to Australia for planting in impounded systems called ‘ponded’ pastures, especially where the created water levels became too deep for the preferred wet pasture para grass Urochloa mutica. Ponded pastures were commonly constructed in northern Australia in the 1970s to produce green fodder during the seasonally dry winter period (Weier et al., 1995). Seed introduced in 1973 for experimental plantings was commercially released to the Queensland grazing industry in 1988 under the cultivar name ‘Olive’ (Broue, 1973; Australian Department of Agriculture, 2013). The original seed was acquired from the International Research Institute, Tucupita, Venezuela, yet is believed to have originated from the Caribbean island of Hispaniola (Oram, 1989). Within a few years, it was noticed that plants had escaped from the constructed wet pasture paddocks through the constructed canals and waterway systems.

In 1995, the first natural and hydrologically isolated wetlands had already been identified as invaded [Clarkson #10314 (BRI)]. In 1996, H. amplexicaulis reached pest proportions in the low-lying coastal sugar cane systems downstream (Csurhes et al., 1999). By 2000, at least 1000 hectares in Australia were infested. Soon after new invasions were documented all along the Queensland coastal zone and were identified in the Northern Territory. By 2011, infested land had increased over tenfold to 11,000 ha, mostly the result of escapes from plantings (Australian Weeds Committee, 2012). Within one year plants has spread south to enter New South Wales, along the northern coastal zone, just north of Coffs Harbour (Council of Heads of Australasian Herbaria, 2014). These most recent occurrences in New South Wales occur at 30° S latitude and represent the southernmost introduced extent of H. amplexicaulis worldwide.

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Australia Venezuela 1973-1990 Yes Australian Department of Agriculture (2013); Broue (1973); Weier et al. (1995) Rhizomes planted for ponded pasture

Risk of Introduction

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Seeds prove the highest risk for long distance and new introductions, whether through biotic, climactic, or human mediated means. The method by which H. amplexicaulis was introduced to the USA is not clear, although it is more likely to have been intentionally introduced as a pasture grass rather than accidentally introduced from the neighbouring Caribbean native range via migrating waterfowl.

H. amplexicaulis is restricted as a quarantine pest in Australia only, and so accidental or purposeful introductions might continue globally with ease. Tropical countries of Asia and Malaysia could become interested in introducing H. amplexicaulis as a forage species that can tolerate flooding, especially as sea levels rise (as in Premaratne and Permalal, 2008). In Mexico, and perhaps the Caribbean, H. amplexicaulis remains valued as a forage crop for wet pastures (Enriquez-Quiroz, 2006); it has been shown to provide high protein and digestible matter when grown under wet conditions (Kalmbacher et al. 1998).

Habitat

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H. amplexicaulis prefers seasonally inundated, open habitats such as lowland floodplain marshes and savannas, marsh ponds, isolated depressions and the sunny margins of swamps, rivers, lakes and streams. It extensively invades native wetlands, where it forms monocultures under relatively natural hydrological disturbance regimes.

In agricultural and urbanized areas it can colonize flooded fields of rice and sugar cane and the ditches, canals, and dams that serve it. Even in its native range, it is not unusual to find H. amplexicaulis in natural wetlands habitats that are adjacent to cultivated land.

This species grows best under fluctuating systems of shallow water up to 1.5 m deep. In permanent wetlands the species will persist if water levels do not exceed 1.2 m. Populations have been known to remain growing and rooted in depths of 3 m for at least nine months, yet higher water levels, such as during flooding, will induce rhizomes to break and form free floating mats (Australian Department of Agriculture, 2013).

Where introduced in the USA and Australia the habitats invaded by H. amplexicaulis compare to those of its native range. In Florida it is found in floodplain marshes and the margins of hardwood swamps, of the typically expansive and low elevation river basins of central and south central Florida. In Australia, H. amplexicaulis is widely distributed in Queensland and the Northern Territory within the waterways and wetlands of the coastal and subcoastal zones.

In Bolivia, H. amplexicaulis plants span the country in communities from semi-deciduous rainforests to Amazonian savannas (Missouri Botanical Garden, 2014).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Other
Soil Present, no further details Harmful (pest or invasive)
Soil Present, no further details Natural
Terrestrial
 
Terrestrial – ManagedCultivated / agricultural land Secondary/tolerated habitat Harmful (pest or invasive)
Cultivated / agricultural land Secondary/tolerated habitat Natural
Managed grasslands (grazing systems) Secondary/tolerated habitat Harmful (pest or invasive)
Managed grasslands (grazing systems) Secondary/tolerated habitat Productive/non-natural
Disturbed areas Principal habitat Harmful (pest or invasive)
Disturbed areas Principal habitat Natural
Terrestrial ‑ Natural / Semi-naturalNatural forests Secondary/tolerated habitat Harmful (pest or invasive)
Natural forests Secondary/tolerated habitat Natural
Natural grasslands Principal habitat Harmful (pest or invasive)
Natural grasslands Principal habitat Natural
Riverbanks Principal habitat Harmful (pest or invasive)
Riverbanks Principal habitat Natural
Freshwater
Irrigation channels Principal habitat Harmful (pest or invasive)
Irrigation channels Principal habitat Natural
Lakes Principal habitat Harmful (pest or invasive)
Lakes Principal habitat Natural
Reservoirs Principal habitat Harmful (pest or invasive)
Reservoirs Principal habitat Natural
Rivers / streams Principal habitat Harmful (pest or invasive)
Rivers / streams Principal habitat Natural
Ponds Principal habitat Harmful (pest or invasive)
Ponds Principal habitat Natural

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Eleocharis (spikerush)CyperaceaeWild host
Oryza sativa (rice)PoaceaeMain
Panicum hemitomonPoaceaeWild host
Saccharum officinarum (sugarcane)PoaceaeMain

Growth Stages

Top of page Fruiting stage, Post-harvest, Pre-emergence, Seedling stage

Biology and Ecology

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Genetics

Chromosome number: 2n = 20 (Pohl and Davidse, 1971; Honfi et al., 1990).

H. amplexicaulis spontaneously crosses with the native Australian wetland species H. acutigluma to produce a new hybrid species, H. x calamitosa, in tropical Australia (Clarkson et al., 2011).

Reproductive biology

H. amplexicaulis reproduces by seed and by rhizome fragments. Seeds have the capacity to germinate within 48 hours of their deposition on waterlogged soil. Germination typically occurs at the end of the wet season and, if water remains available, maturation is completed within three months. At maturity, a single inflorescence can produce more than 4000 seeds (Australian Weeds Committee, 2012).

Physiology and phenology

Introduced USA range: Flower and fruit: Sept - Nov

Introduced Australian range: Flower April-Jun; Fruit ~Nov-Jan

Native Central and South American range: Flower and fruit: Jul–Jan

H. amplexicaulis, like other C-3 grass species from seasonal savannas in central Venezuela, has a high leaf area index and achieves high photosynthetic productivity despite the very low nutrient availability at which it grows (Anten et al., 1998).

The adaptation of H. amplexicaulis to flooding corresponds to its capacity for rapid stem elongation and the formation of adventitious roots. When flooded, submerged leaves senesce rapidly, but nodes produce adventitious roots and the growth of leaves increases, presumably maintaining the effective photosynthetic leaf area (Kibbler and Bahnisch, 1999).

Longevity

Long-lived perennial populations persist through rooted basal portions and rhizomes. In Australia, large, seasonally flooded stands of H. amplexicaulis have remained strong for more than 20 years (Australian Weeds Committee, 2012).
 
Minimal data is available on seed longevity under natural environmental conditions, but trials indicate seed viability may remain as high as 8 to 24% after eight years in the soil seed bank (Australian Department of Agriculture, 2013).

Population Size and Structure

Creeping, sprawling and heavily branched populations root in the substrate, with lower culms decumbent and submersed and upper stems erect and emergent. Plants reportedly grow to a height of 2.5 m, although 1-1.5 m is more typical. Dense, free-floating mats can develop in deeper water (up to 4 m) usually in response to flooding (Australian Department of Agriculture, 2013)

Nutrition

Material grown on pond margins in the flatwoods cattle range lands of southern Florida was valued at 56 g/kg crude protein and 47.4% in vitro organic matter digestion (IVOMD) (Kalmbacher et al., 1998)    

Associations

In its native range in the Rio Doce river in Minas Gerais, Brazil, H. amplexicaulis was associated with other primary invasive plant species: Eichhornia crassipes, Salvinia molesta, Paspalum repens, Oxycarum cubense and Urochloa subquadripara (Pitelli et al., 2014).

In the seasonal floodplain of the Pantanal, Brazil, H. amplexicaulis and its native associates Eleocharis elegans, Aeschynomene fluminensis and Hydrolea spinosa have been recommended as biological indicators for detecting marsh pond communities (Pinder and Rosso, 1998).

H. amplexicaulis, Leersia hexandra, Sacciolepis striata and Polygonum acuminatum were among the most important species numerically at a herbaceous wetland of a tropical lake in Monagas, Venezuela (Gordon, 2000).

Environmental requirements

H. amplexicaulis responds well to alternating periods of flooding and dryness in open, sunny environments. Seasonality during the hydroperiod is important for the continuation of vigorous, long-term populations.

H. amplexicaulis is a freshwater wetland species with little salt tolerance and will not persist in salt water of moderate to high concentrations for even part of the year (Australian Dept. of Agriculture, 2013).

Climate

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ClimateStatusDescriptionRemark
A - Tropical/Megathermal climate Preferred Average temp. of coolest month > 18°C, > 1500mm precipitation annually
Af - Tropical rainforest climate Preferred > 60mm precipitation per month
Am - Tropical monsoon climate Preferred Tropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))
As - Tropical savanna climate with dry summer Tolerated < 60mm precipitation driest month (in summer) and < (100 - [total annual precipitation{mm}/25])
Aw - Tropical wet and dry savanna climate Preferred < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
28 -34

Air Temperature

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Parameter Lower limit Upper limit
Mean annual temperature (ºC) 10 22
Mean maximum temperature of hottest month (ºC) 16 28
Mean minimum temperature of coldest month (ºC) 6 14

Rainfall

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ParameterLower limitUpper limitDescription
Mean annual rainfall80115mm; lower/upper limits

Rainfall Regime

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Soil Tolerances

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Soil drainage

  • impeded
  • seasonally waterlogged

Soil reaction

  • acid
  • neutral

Soil texture

  • light
  • medium

Special soil tolerances

  • infertile
  • shallow

Notes on Natural Enemies

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Ischnodemus variegatus (Signoret), a true bug (Hemiptera) belonging to the family Blissidae, is native to Central and South America and appears be host specific to H. amplexicaulis (Baranowski, 1979; Diaz et al., 2008).

I. variegatus is recently adventive to Florida (Overholt et al., 2004) where its sap feeding can induce symptoms of foliar stress, foliar necrosis and reduced seed production on H. amplexicaulis when it grows in marginal environments. Plants growing in resource rich environments, however, such as deep floodplains with high nutrient runoff, can sustain damage by I. variegatus without suffering reduced reproductive output (Montemayor et al., 2013).

Means of Movement and Dispersal

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Natural dispersal

Seed and stem fragments may be dispersed by water movement.

Vector transmission (biotic)

Seed dispersal by native fish through their feeding and excrement has been recorded in seasonal wetlands of Pantanal, Brazil (Silveira and Weiss, 2014). Although aquatic birds and other animals are expected to be involved in the short and long distance movements of H. amplexicaulis throughout the neotropics, no particular supporting evidence has been provided for this species.  

The plant may have been transported by magpie geese Anseranas semipalmate in the wetlands of northern Australia(Australian Weeds Committee, 2012).

Intentional introduction

H. amplexicaulis has been planted in northern Australia as a culm spieces in low fertility, ponded pasture systems for cattle grazing (Csurhes et al., 1999), and to suppress seedling growth of Mimosa pigra (Australian Weeds Committee, 2012).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Animal productionDeliberate plantings for cattle grazing escaped through drainage systems to colonize agricultural, u Yes Yes Australian Weeds Committee, 2012
Digestion and excretionSeed dispersal by native fish in seasonal wetlands of the Pantanal, Brazil; likely waterfowl Yes Yes Australian Weeds Committee, 2012; Silveira and Weiss, 2014
DisturbanceDitching, dyking and diversion of natural stream and river systems affecting both substrate and flow Yes Yes Australian Weeds Committee, 2012; Silva et al., 2012
Escape from confinement or garden escapeDownstream spread through natural and engineered waterways after escape from ponded pastures in Aust Yes Yes Australian Weeds Committee, 2012
Flooding and other natural disastersSpread of vegetative fragments through natural and engineered waterways Yes Yes Australian Weeds Committee, 2012
Hunting, angling, sport or racingPotential contaminant on water gear, equipment, vehicles Yes Yes Australian Weeds Committee, 2012
Interbasin transfersPotentially through waterfowl Yes Australian Weeds Committee, 2012
Interconnected waterwaysSpread with water flow through natural and engineered waterways Yes Yes Australian Weeds Committee, 2012

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessionsSeeds potential contaminant on water gear Yes Yes Australian Weeds Committee, 2012
Floating vegetation and debrisFragments of stolon Yes Australian Weeds Committee, 2012
Machinery and equipmentSeeds potential contaminant on machinery and vehicles Yes Yes Australian Weeds Committee, 2012
Soil, sand and gravelSubstrate contaminating gear, equipment, machinery, vehicles Yes Yes Australian Weeds Committee, 2012
WaterSpread with water flow through natural and engineered waterways Yes Yes Australian Weeds Committee, 2012

Impact Summary

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CategoryImpact
Economic/livelihood Positive and negative
Environment (generally) Negative
Human health Negative

Economic Impact

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H. amplexicaulis is reportedly difficult and costly to treat in Australia due to the wet environments it inhabits and the need for repeated treatment to exhaust the seed bank.

Low-lying sugarcane fields and their drainage and irrigation systems are at particular risk for invasion in Australia (Australian Weeds Committee, 2012) as are similar agricultural systems for rice in Brazil (Silva et al., 2012) and in Louisiana, USA (Urbatsch and Saichuk 2014). Costs of farm management are greatly increased with invasion (Australian Weeds Committee, 2012).

The incomes of barramundi (Lates calcarifer) fisheries are threatened by the degradation of barramundi wetland nurseries following invasion of H. amplexicaulis (Australian Weeds Committee, 2012).

The plant’s tendency to produce large, monospecific stands that acclimate to hydrological fluctuations severely impacts hydroelectric systems in urbanized regions within its native range (Silva et al., 2012). H. amplexicaulis has impacted engineered rivers at hydroelectric dams in Rio Dulce and Rio de Janeiro.

Environmental Impact

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Impact on habitats

H. amplexicaulis extensively invades native wetlands, where it forms monocultures under relatively natural hydrological disturbance regimes.

Australia

In the Fitzroy River backwaters of central Queensland, Australia, the replacement of extensive zones of floating-attached and submergent native vegetation by monoculture stands of H. amplexicaulis resulted in a 30-fold increase in wetland plant biomass, but a significant decline in the number of plant species. These changes in vegetation structure were found to influence macroinvertebrate and fish faunal composition. Macroinvertebrates communities were significantly reduced, except for the order Coleoptera, which were more abundant. Populations of the introduced fish Xiphophorus maculatus comprised 75% of the fish captured in H. amplexicaulis beds, compared with 0% of the fish species captured in native plant beds (Houston and Duivenvoorden, 2002), suggesting the presence of H. amplexicaulis monocultures also encouraged invasive fish populations.

Dissolved oxygen levels within dense aquatic stands of H. amplexicaulis have been measured at 17% saturation, well below the minimum 30% required to prevent acute stress in local fish species (Australian Weeds Committee, 2012). In addition, fish movement is likely impeded by the physical barrier of the dense plant populations (Australian Weeds Committee, 2012).

Waterbirds, such as the magpie goose Anseranas semipalmate, depend on a range of wetland plants including native sedges and Hymenachne acutigluma for food and secure roost sites. It is not known what impact the extensive, pure stands of H. amplexicaulis may have on bird populations (Australian Weeds Committee, 2012).

H. amplexicaulis has been found in the Kakadu National Park in Northern Territory, a World Heritage Site, and the  Lakefield National Park in Queensland, containing extensive wetland systems and rare species (Natural Heritage Trust, 2003; Clarkson et al., 2012).  

Florida, USA

In the following conservation areas in Florida H. amplexicaulis can be found altering the species composition and structure of open, seasonal marsh and floodplain communities:

The Myakka Wild and Scenic River – H. amplexicaulis monocultures across the entire floodplain marsh

Six Mile Cypress Preserve – found along edges of cypress strand swamp

Lake Okeechobee, Fisheating Bay – in shallow, protected nesting areas for migrating waterfowl

St. Johns Marsh and Reedy Creek Swamp – both expansive open marsh in distinct drainage systems

Wingate Creek State Preserve and Deer Prairie Creek Preserve – H. amplexicaulis replacing natural habitat

Impact on biodiversity

The invasion of H. amplexicaulis into natural wetland habitats of the tropics of northern Australia has resulted in hybridization with the indigenous species H. acutigluma (although The Plant List lists H. acutigluma as a synonym of H. amplexicaulis). Hybridization events, initially detected by intermediacy in morphological character traits from plants at Abattoir Swamp and Beatrice Creek, Northern Territory, were confirmed by molecular analysis and concluded by the formal description of the new hybrid H. x calamitosa (Clarkson et al., 2011). The hybrid H. x calamitosa has the propensity to be at least as invasive and environmentally destructive under Australian conditions as is H. amplexicaulis (Clarkson et al., 2011). Because hybridization has been detected between the exotic and indigenous species at two widely spaced locations, it may be occurring as a common event (Clarkson et al., 2011) across the Australian range of H. acutigluma, wherever the two species coexist. The corruption of an indigenous genotype is a direct and measurable loss to global biodiversity, and while the production of a new hybrid species may be considered an addition to the global tally, its conservation significance ranks very low.

Social Impact

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Large, monospecific stands of H. amplexicaulis have been associated with the increased abundance of two species of mosquitoes, one of which vectors the Ross River virus. The association is believed to be a response of the inability of fish to feed on mosquito larvae in thick monocultures. Subsequent herbicide treatment of dense stands presents the alternative risk of degrading the quality of public water stores (Australian Weeds Committee, 2012).

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Pioneering in disturbed areas
  • Highly mobile locally
  • Benefits from human association (i.e. it is a human commensal)
  • Long lived
  • Fast growing
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Reproduces asexually
Impact outcomes
  • Altered trophic level
  • Changed gene pool/ selective loss of genotypes
  • Conflict
  • Ecosystem change/ habitat alteration
  • Infrastructure damage
  • Modification of hydrology
  • Modification of natural benthic communities
  • Modification of successional patterns
  • Monoculture formation
  • Negatively impacts agriculture
  • Negatively impacts livelihoods
  • Negatively impacts aquaculture/fisheries
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
  • Soil accretion
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Impact mechanisms
  • Competition - monopolizing resources
  • Competition - shading
  • Fouling
  • Herbivory/grazing/browsing
  • Hybridization
  • Rapid growth
  • Rooting
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Highly likely to be transported internationally deliberately
  • Difficult to identify/detect as a commodity contaminant
  • Difficult/costly to control

Uses

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Economic value

The potential trade-off of the positive impact of H.amplexicaulis as a pasture crop outside of ponds or floodplains is questionable. The species has shown to be valuable to cattle production in ponded pasture systems in Queensland and on alluvial flood plains of Northern Territory, Australia. Although it escapes to wetlands, watercourses and other unexpected wet areas, many landholders are reluctant to implement control due to the forage benefits it is believed to have and the expense and large efforts required for control. Meanwhile the authorities report that cattle largely ignore H. amplexicaulis in Australia when other food sources are available (Australian Government, Dept. of Env., 2014).

The plant is a highly valued forage in its native range in Mexico, Cuba and Venezuela (Diaz et al., 2008). Producers indicated that H.amplexicaulis is beneficial for milk production compared with other forage grasses growing in flooded tropical savanna conditions (Enriquez-Quiroz et al., 2006), and it has been shown to provide high protein and digestible matter when grown under wet conditions (Kalmbacher et al., 1998).

Environmental services

H. amplexicaulis is one of the most commonly consumed plants of the capybara (Hydrochaeris hydrochaeris) in the flooded savannas in Cano Limon, Colombia, composing 16.9% of the animal’s total diet (Forero-Montana et al., 2003).

Uses List

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Animal feed, fodder, forage

  • Forage

General

  • Research model

Diagnosis

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A tetrazolium staining technique had been presented for viability determination in seed of H. amplexicaulis. The imbibition of seeds without glumes, for six hours, with subsequent immersion in a solution of tetrazolium 0.5% for four hours was effective in assessing viability (da Silva et al., 2012).

Detection and Inspection

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Diagnostic features of the genus Hymenachne include its aquatic habit and lower internodes filled with spongy aerenchyma, the cylindrical inflorescence, the margins of the upper lemma being flat and the glumes not saccate (Webster, 1987). In Australia, the genus is ultimately characterized from other Panicae by the first glume which encircles the spikelet base (Webster, 1987).

Commodity inspectors should be wary of contamination in rice seed, especially rice grown in Central and South America or Louisiana, USA. Inspectors should look for the spikelets, which are light in colour, flattened, and only a few millimetres long; the actual seed/fruit (caryopsis) is too small to detect with the unaided eye.

A trained botanist having intact, mature spikelets may find them possible to identify using the illustration provided (see Images, above) and the following characters:

1)     Lower glume wrapping the base of the spikelet and small, appearing only 1.3 as long as the spikelet and wedge shaped at the tip, 3-5 nerved and scabrous on the keel.

2)     Lower lemma 3.6-4.6 mm, 5 nerved and tapering gradually to a long point, longer than the fruit, margins flat, and scabrous on the nerves.

3)     Upper glume 2.8-3.9 mm long, 5 nerved and scabrous on the nerves.

Vegetative material may be less likely to be transported, but is easier to recognize. Use the illustration above to focus on:

1)     Leaf blade flat with base auriculate and clasping

2)     Leaf glabrous except for the base having a few long hairs

3)     Stems solid

4)     Nodes with adventitious, spongey roots

Similarities to Other Species/Conditions

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In Australia, efforts are made to relay the distinction between the introduced H. amplexicaulis and the native H. acutigluma, to resource managers and cattle ranchers. The two are similar in growth habit and nearly alike in floral features. They are distinguished by observable differences in their gross anatomy, H. amplexicaulis being larger and more robust in size with leaves that are basally lobed and loosely clasping the stem. The margins of these clasping lobes are set with long hairs. The Austalian native H. acutigluma has narrower, linear to linear-lanceolate leaves which are not lobed nor clasping at the base (Csurhes et al., 1999; Cowie et al., 2000). H. acutigluma may be variable in habit and in the size of the spikelets and flowers throughout the year (Webster, 1987). H. acutigluma is found in Arnhem (Northern Territory) and in Cape York and Burdekin (Queensland), where it inhabits wet sclerophyll forests, back-water swamps, floodplains and coastal grasslands (Calder, 1981; Webster, 1987). It also grows in floating mats (Cowie et al., 2000).

There are no native species of the genus Hymenachne in North America; however, American cupscale, Sacciolepis striata (L) Nash, is a common native plant with a morphological profile and habitat requirements strongly similar to those of Hamplexicaulis. Both species are large, rhizomatous and sprawling, with erect culms and elongated, congested spike-like panicles. Both grow in shallow wetland and open riparian habitats. Field biologists should look closely at the internodes, the leaf base, the spikelet bases, and the glumes - all which bear features to distinguish the two. In Hamplexicaulis the internodes are solid and pithy, the base of the leaf is strongly auriculate and clasping to the culm, the glumes are non-saccate and 5-nerved, and the spikelets are symmetrically attached to the pedicel. In S.striata the internodes are hollow, the base of the leaf does not strongly clasp the culm, the secondary glume is saccate and bears 11-12 nerves, and the spikelets are asymmetrically attached to the pedicel (Urbatsch and Saichuk, 2014).

H. pseudointerrupta is a related species found in the Indo-Malayan region, with a wide Asian distribution ranging from the equatorial tropics to warm temperate regions (Bor, 1960; Koyama, 1987; Shukla, 1996; Dassanayake and Claton, 1996; Csheres, 1999; Editorial Committee of the Flora of Taiwan, 2000; Kew Herbarium Catalogue, 2014).

Prevention and Control

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SPS measures

As a declared weed across Australia, H. amplexicaulis is prohibited by a range of at least eight different legislative acts affecting agriculture and land management actions particular to each territory. Legislation is based on whether or not the species is yet established in that territory (Australian Government, Dept. of Env., 2014).

In Western Australia, legislation directs not only exclusion, but control, including searches at border patrols, to prevent first entry and establishment. Southward in Victoria, South Australia and Tasmania, its importation, sale, distribution, and introduction as a contaminant in freely moving commodities is prohibited (Australian Government, Dept. of Env., 2014).

Public awareness

The Australian Government, Dept. of Env. (2014) recommends extension and awareness activities and materials, including field days and conducting forums, preparation and delivery of resource kits, signage for recreational waterholes, and media coverage.

Eradication

The Noxious Weeds Act of 1993 requires the continuous eradication of H. amplexicaulis from all land in New South Wales (Australian Government, Dept. of Env., 2014). This act was in place long before the species invaded the northeastern region.

In the Northern Territory and Queensland, Australia, where infestations remain widespread, the Weeds Management Act of 2001 requires land managers to control the plant’s growth and prevent spread (Australian Government, Dept. of Env., 2014). Eradication is not emphasized here as its attainment is unlikely.

Containment/zoning

In Australia, efforts continue to reduce the spread of H. amplexicaulis outside of planted pasture systems, using a variety of small to large scale plans:

- A spatially explicit decision method for resource managers to identify actions to manage H. amplexicaulis at local levels while minimizing costs and likelihood of reinvasion has been developed (Januchowski-Hartley et al., 2011).

- Guidelines have been produced that detail methods for containing plants to genuine grazing systems in Queensland, including requirement of a permit to introduce, keep or supply plant material (Australian Government, Dept. of Env., 2014).

- A strategic approach to prevention and management was prepared through the comparative use of four models. Built on data for climate, distribution, and connectivity of drainage systems, the models were consistent in identifying a number of catchments of high invasion risk or spread in northern, central and southern Australia to which the directing of management priority has been suggested (Wearne et al., 2013).

- Geographic differentiation of management objectives have been proposed for a large, continent-wide management strategy of H. amplexicaulis in Australia (Grice et al., 2011).

Physical/mechanical control

Manage grazing systems to reduce seed production (Australian Government, Dept. of Env., 2014).

Movement control

The Australian Government, Dept. of Env. (2014) recommends maintaining a 50 m buffer on external fence lines, creeks and drainage lines, and encouraging strong grass pasture in buffer zones.

Biological control

An effective biological control agent has not been determined for H. amplexicaulis, although studies have been made.

The sap-feeding bug Ischnodemus variegatus, discovered on H. amplexicaulis in Florida, has been found to reduce the plant’s growth rate and biomass (Overholt et al., 2004). I. variegatus is predicted to complete three to five generations per year in areas where its host plant has invaded Florida (Diaz et al., 2008). Laboratory studies found that it developed and survived best on H. amplexicaulis (23.4% survival) than on other genera tested (Diaz et al., 2009) and that it performed poorly overall on H. acutigluma when compared to H. amplexicaulis (Diaz et al., 2010).

An undescribed Delphacidae species found naturally occurring on H.acutigluma in Australia did not occur nearby on H. amplexicaulis and did not develop on H. amplexicaulis in laboratory tests.  The insect species proved to be host specific to H. acutigluma, causing yellowing and weakening of that species under high densities in the laboratory (Bell et al., 2011).  

Chemical control

Produced in 2006, a full control guide including case studies is available online (Australian Government, Dept. of Env., 2014). Details include the use of commercial herbicides and strategic goals, such as treating plants before they reach maturity and set seed, and eradicating outlier infestations not used in grazing systems.

Regardless of water depth, glyphosate + imazapyr reduced biomass of H. amplexicaulis by as much as 97% when compared to the untreated control (Sellers et al., 2008).

In greenhouse experiments in Brazil, young annual plants were killed after treatment with glyphosate and a formulated mixture of imazapic and imazapyr; older, perennial plants, however, were not killed (Silva et al., 2012).

Adapted from Cook et al. (2005): Haloxyfop-R methyl was reported to be most effective against H. amplexicaulis, resulting in 100% mortality. Imazapyr and fluazifop-butyl can give 90% mortality, and the isopropylamine salt of glyphosate 50%. Repeated applications of foliar spray may be necessary to control dense infestations. Application of glyphosate followed by burning of dead tops can give significant control, providing mature seed has not dropped before treatment. However, imazapyr and glyphosate are broad-spectrum herbicides and should be used with care, and care should also be taken that large quantities of dead plant material from sprayed plants do not contaminate bodies of water.

Monitoring and surveillance (incl. remote sensing)

Property should be monitored for new infestations regularly, particularly following rainfall and flood events (Australian Government, Dept. of Env., 2014).

Gaps in Knowledge/Research Needs

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Necessary data is lacking on the applied aspects of seed viability, dormancy, and the environmental requirements for successful germination and recruitment in potentially new habitats. This severely restricts the ability to adequately predict the risk of biological invasion through seed. 

References

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Australian Department of Agriculture, 2013. Hymenachne fact sheet. Fisheries and Forestry. http://www.daff.qld.gov.au/

Australian Government; Deptof the Environment, 2014. Threat abatement advices. http://www.environment.gov.au/biodiversity/threatened/threat-abatement-advices/invasive-pasture-grasses-olive-hymenachne

Australian Weeds Committee, 2012. Olive hymenachne (Hymenachne amplexicaulis (Rudge) Nees) strategic plan 2012-17. http://www.environment.gov.au/biodiversity/threatened/threat-abatement-advices/invasive-pasture-grasses-olive-hymenachne

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Bell KL; Heard TA; Klinken RDvan, 2011. Natural enemies of invasive Hymenachne amplexicaulis and its native congener in Australia and the potential for biological control. Biological Control, 57(2):130-137.

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Diaz R; Overholt WA; Heard TA; Samayoa A; Klinken RDvan, 2010. Characterizing the host specificity of Ischnodemus variegatus (Signoret) (Hemiptera: Blissidae) on two congeneric grass species. Biological Control, 55(3):219-224.

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Links to Websites

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WebsiteURLComment
GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gatewayhttps://doi.org/10.5061/dryad.m93f6Data source for updated system data added to species habitat list.
Threat abatement advice for a key threatening species Hymenachne amplexicaulishttp://www.environment.gov.au/biodiversity/threatened/threat-abatement-advices/invasive-pasture-grasses-olive-hymenachne

Contributors

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28/12/14 Original text by:

Colette Jacono, University of Florida, USA

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