Hymenachne amplexicaulis (Rudge) Nees
Panicum amplexicaule Rudge
Hymenachne acutigluma auct. non (Steud.) Gilliland
Family: Poaceae (alt. Gramineae) subfamily: Panicoideae tribe: Paniceae.
hymenachne, west indian marsh grass, water straw grass, trompetilla or trumpet grass, canutillo (Colombia); dal (dhal) grass, bamboo grass (India); carrizo chico, cañuela blanca (Bolivia); bamboegras (Suriname); chingolo (Paraguay).
A perennial, stoloniferous grass, with robust, erect or ascending culms 1-2.5 m high and to >12 mm thick, and prostrate stems that run on wet ground, or float on water, developing adventitious roots. Stems glabrous, pithy. Leaves glossy green in colour, largely glabrous; sheaths often spongy; blades mostly linear-lanceolate, 10-45 cm long and to >3cm wide, cordate, auriculate and clasping (amplexicaul) at base; ligule membranous. Panicle narrow, spikelike, cylindrical, 20-50 cm long, 8 mm diameter, sometimes with 2 to a few long, upright branches. Spikelets lanceolate, dorsi-ventrally compressed, upright, 3-4 (-5) mm long and 1 mm diameter; c. 2.3 million seeds/kg. Caryopsis easily detached, 1-2 mm long and 0.6 mm diameter.
H. amplexicaulis is morphologically similar to H. acutigluma (Steud.) Gilliland and H. pseudointerrupta C. Muell. (recognised in Asia, possibly synonymous with H. acutigluma), but can be distinguished by virtue of its cordate, stem -clasping leaf base.
Native to or naturalised in:
North America: USA (Florida), Mexico.
Mesoamerica: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama.
Caribbean: Cuba, Dominican Republic, Haiti, Jamaica, Trinidad.
South America: Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, Venezuela.
Morphologically similar to, but distinct from Hymenachne acutigluma (Steud.) Gilliland, which is native to:
Continental Asia : China (Yunnan), India, Myanmar, Thailand, Viet Nam.
Malesia: Indonesia (Kalimantan), Malaysia.
Australasia: Australia (Northern Territory, Queensland), Papua New Guinea, and Polynesia.
H. amplexicaulis has value as a cool or dry season forage in seasonally inundated land, and can also be cut for silage. Stems are too thick for effective hay -making, although it can be used in cut-and-carry systems as green feed. It is proposed as a nutrient sink and sediment trap in situations polluted by habitation and cultivation.
Grows well on fertile, seasonally inundated clays, although distribution is determined more by availability of water than by soil texture .
H. amplexicaulis is a wetland species, inhabiting margins of swamps, river floodplains, and drainage canals, mostly in water to about 2 m deep, occasionally extending into water 3-4 m deep. It can be grown for pasture in natural or artificially inundated pondage areas. On seasonally flooded floodplains, it needs over 1 m of water during the wet season to persist. It has low drought tolerance, not spreading beyond the wet zone, and low salt tolerance, not surviving even occasional tidal impact.
Occurs from about 29ºN in Florida and 19ºN in Mexico to about 28ºS in Argentina, mostly at low altitudes (<850 m asl, but reportedly to 1,500 m asl). This is equivalent to a range in average annual temperatures of 21-26ºC, with some frost incidence at the extremes. H. amplexicaulis appears better adapted to slightly lower temperatures than is H. acutigluma.
Tolerant of only light shade.
Appears to be primarily a short day plant with a critical daylength of about 12 hours. Flowering also appears to be stimulated in response to an extended, more intense wet season. Although plants can largely flower throughout the growing season , there is a peak flowering from March/April to late June in the southern hemisphere or September/October to late December in the northern hemisphere.
H. amplexicaulis is a valuable fodder resource for the dry season. It is normally not grazed at other times of the year due to the harmful effects of trampling and uprooting of plants from wet soil. Stands are normally stocked at one beast per 1.5-2 ha.
By virtue of its habitat, fire is uncommon. However, fire following herbicide application can stimulate seedling growth if mature seed has fallen before herbicide treatment.
Guidelines for the establishment and management of sown pastures.
H. amplexicaulis can be established vegetatively or from seed. Stem cuttings (2-3 nodes) can be dropped into water over 10 cm deep, or runners planted in rows 5 m apart. Seed can be broadcast onto wet soil, or onto shallow water, with seedlings emerging as the pond dries out. Sowing rates of 1-2 kg seed/ha are usually adequate. Seed viability declines fairly quickly under ambient storage conditions in the tropics (20-30ºC), from an initial 98% to 10% over a period of 16 months.
25-50 kg/ha N can be applied to sparse or newly established stands to promote tiller development. Plants appear to obtain nitrogen from a non-symbiotic association with nitrogen-fixing bacteria or cyanobacteria around the roots and submerged stems, reducing the reliance on fertilisers. Nitrogen fixation rates are believed to be higher in newly established stands compared with mature stands, which draw nutrient from litter decomposition and mineralisation, and eutrophication. N and P fertilisers applied at the beginning of the wet season have little effect on dry matter yield, or CP or P levels in the plant in the long term.
Compatibility (with other species)
Tends to suppress companion species.
Pests and diseases
H. amplexicaulis is susceptible to fungal diseases, a leaf spot caused by Curvularia lunata and a tar spot caused by Phyllachora sp. Neither fungus is sufficiently aggressive to be a useful biocontrol agent.
In Australia, rice leaffolder (Marasmia sp.) larvae attack H. amplexicaulis and H. acutigluma, causing leaf tip necrosis, much more severe in the former. Larvae of the Ocola skipper (Panoquina ocola) also feed on hymenachne. A lygaeid bug (Ischnodemus variegatus) can kill stands in localised areas in Florida, but infestations do not spread sufficiently to kill whole stands. The paddy bug (Oebalus poecilus and O. ypsilongriseus), also known as "ghundi" or "bush bug", a serious pest of rice in the Caribbean, feeds on H. amplexicaulis ), migrating to rice crops during early flowering.
Ability to spread
Seed is dispersed by floodwater and by water birds. Pieces of plants can be carried to new locations on hooves of grazing animals, or in moving water. Rafts of plant material have been moved by water flow, until lodging against a bank and taking root. It has also been moved by man for use in pasture development. Surface seed has survived for 1-2 years, and buried seed for >3 years.
H. amplexicaulis displaces native wetland vegetation, and blocks drainage canals. It has become an environmental weed in Florida, USA, and its planting and use is now restricted in Australia, where it has been declared one of 20 Weeds of National Significance (WONS).
Unlike most tropical grasses, hymenachne employs the C3 photosynthetic pathway, which usually results in lower lignin content of the herbage. Crude protein levels in whole tops varies from 9-21 (rarely to 30)% at different times of year, with leaf levels up to 25% and stem 9%. CP digestibility mostly ranges from 66-80%, being higher in stems than in leaves. TDN values range from 54-76%. P levels mostly vary from 0.16% or over during the dry season to 0.20% or over during the wet season. Sodium levels are low (0.02%) compared with levels in Echinochloa polystachya (0.10%) and Brachiaria mutica (0.33%).
While generally readily eaten by cattle and buffaloes, even when mature, it is not as palatable as Brachiaria mutica or Echinochloa polystachya . Important feed component for the giant rodents, capybara or carpincho (Hydrochaeris hydrochaeris), found in its native habitat.
Herbage contains high levels of moisture. DM yields are commonly of the order of 5-10 t/ha/yr, although >18 t/ha/yr DM has been recorded.
Estimated carrying capacity of 1 beast/ha, with an average liveweight gain of 180 kg per beast per annum.
2n = 20; breeding system unknown.
Seed has been produced commercially in large artificial ponds, from which the water can be pumped out prior to harvest by adapted machinery.
Haloxyfop-R methyl has proven the most effective control agent, giving 100% kill. Imazapyr and fluazifop-butyl can give 90% kill, and the isopropylamine salt of glyphosate, a 50% kill. Repeated applications of high volume foliar spray may be necessary to control dense infestations, since, although tops might be killed by a single application, stands recover from stolons and seed within 3 months. Imazapyr and glyphosate are broad-spectrum herbicides, and should be used with care. Care should also be taken that herbicides used pose no environmental threat, and are registered for use in the intended manner. Application of glyphosate, followed by burning of dead tops can give significant control, providing mature seed has not dropped prior to treatment. Care should also be taken that large quantities of dead plant material from sprayed hymenachne do not contaminate bodies of water.
- Palatable, high quality feed.
- Maintains quality.
- Dry season feed.
- Can be planted vegetatively or from seed.
- Acts as nutrient sink and sediment trap.
- Invasive (environmental threat).
- Readily spread by animals and water movement.
- Not compatible with other species (forms monocultures).
- Bogdan, A.V. (1977) Tropical Pasture and Fodder Plants (Grasses and Legumes). p. 152 (Longman: London and New York).
- Cabrera, A.L. (ed.) (1970). Flora de la Provincia de Buenos Aires, Coleccion cientifica, Pt. II Gramineas. p. 505. (Instituto Nacional de Tecnologia Agropecuria; Buenos Aires).
|'Olive'||Australia (1987)||Origin uncertain. Released as a source of dry season feed for sub-humid tropics. No longer recommended due to environmental threat.|
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