Aeschynomene americana (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Aeschynomene americana L.

Protologue: Sp. Pl.: 713 (1753).

Family: Leguminosae

Chromosome number: 2n= 20

A. javanica Miquel (1855).

• American jointvetch (Am)
• Indonesia: kacang meongan, asem-aseman, anjang
• Philippines: makahiyang-lalaki (Tagalog), karaparak (Mar.)
• Thailand: sano-don, sano-bok (central), sano khon (north-east)
• Vietnam: pötuk, rokdönao, rui köjing.

American jointvetch is native to the Caribbean and adjacent areas of the Americas between latitudes 30°N and 30°S. It has been introduced into several countries in South-East Asia.

American jointvetch is used as a cut-and-carry forage for animals, and as a hay crop. It is used as a pasture legume in Florida (United States), the tropical east coast of Australia, and Vanuatu. It is also applied as a green manure crop in rice and other cropping systems.

Nitrogen concentrations of green leaf range from 2.5-4.0% and of stems from 0.3-1.0%. In vitro digestibility of leaves is 60-70%. Although tolerant of low soil P, yield and P concentrations respond greatly to applied P. Ripe pods divide into single-seeded segments (seed-in-pod) with 150-220 segments/g. Dehulled or naked seed varies in size with 350-400 seeds/g.

Annual or perennial herb or sub-shrub, growing 1-2 m tall and 1.5-2 m wide, glandular-hispid to subglabrous, with prostrate to erect, hard but pithy main stem 5-10 cm thick at base. Branches form roots where they touch the ground. Habit changes dramatically under grazing where plants branch close to the ground, forming a leafy sward. Leaf 2-7 cm long, pinnately compound, 20-60-foliolate; leaflet more or less sickle-shaped, 3-15 mm × 1-3 mm, glabrous but ciliate at least along one margin, 2-several-costate, folding together at night or when touched. Inflorescence axillary, racemose, few-flowered, about the length of the subtending leaf; pedicel ca. 1 cm long; flower papilionaceous, 3-10 mm long, yellow, orange or mauve, usually with red or purple stripes. Fruit a straight or slightly curved pod, 1-3 cm long, 3-9-articulate; articles (segments) 2.5-5 mm × 3-6 mm, glabrous to villous-hispid, light-brown, more or less muricate, margins thickened. Seed kidney-shaped, 2-3 mm × 1.5-2 mm, dark-brown to blackish.

Plants are heavy seeding, self regenerating annuals or short-lived perennials with crowns surviving up to 2-4 years. The seedling phase is relatively slow, but subsequent growth is rapid in hot and moist conditions. Nodulation is prolific and, under waterlogged conditions, nodules form on lower parts of the main stem and branches. It has a short-day flowering response. Flowering commences 60-200 days after germination, with another 30-60 days to ripe seed. Away from the equator, perennial plants will also flower and seed in spring. Although most of the pollen is shed before flowers open, recent studies indicate that up to 30% outcrossing occurs. Yield of DM is higher in the late maturing types. Up to 90% of freshly harvested seed is "hard" and requires scarification before sowing. Natural breakdown of hardseededness is sufficient to allow re-establishment in the field.

Sometimes A. americana and A. villosa Poiret (syn. A. javanica ) are considered as different species. In that view, A. americana originates from the Caribbean and adjacent areas, usually in wet or moist places, up to 1400 m altitude, and A. villosa originates from southern Arizona (United States) to northern South America and the Antilles, usually in drier areas up to 2250 m altitude. Discriminative morphological characteristics of A. americana and A. villosa would be respectively: flowers 6-8 mm versus 3-5 mm long; leaflets more than, versus less than, 5 mm long; mature fruit-centre muricate versus non-muricate. Young material of both species is impossible to distinguish. Unification of both taxa seems to be justified.

Cultivar "Glenn" was registered for use in tropical coastal Queensland, Australia, in 1983 and "Lee", a more perennial form, in 1991. Common American jointvetch has been used in Florida, United States, since the early 1970s. Descriptions of collections grown in Florida and Australia indicate wide diversity of material differing in range of maturity and perenniality, plant habit and size.

American jointvetch grows in poorly drained and waterlogged conditions. Best growth of American jointvetch occurs in tropical areas with hot, moist climates, normally with an annual average rainfall of over 1000 mm and most commonly in poorly drained or run-on situations. However, its natural distribution covers a wide range of latitude and altitude (up to 2250 m). It should be possible to select for cold tolerance and different rainfall requirements. "Glenn" has a summer minimum rainfall requirement of about 1000 mm. It prefers wet, poorly drained or waterlogged areas on sandy to clay soils.

Suggested seeding rate is 4-8 kg/ha seed-in-pod or 2-4 kg/ha dehulled seed. Half these rates can be used in a mixture. Dehulling is the best method of scarification and will raise germination to about 30%. When sown with a companion grass or grown as a pure stand for forage or hay, it is best sown into a well prepared seed-bed. Satisfactory establishment can be achieved by spreading seed onto the surface of well-grazed pasture.

In grazed pastures, American jointvetch should be kept 50-60 cm tall to promote leaf production. Grazing pressure should be reduced after flowering to promote maximum seed production, particularly in the year of planting. Seed is spread in dung following ingestion by animals.

Commercial seed crops may require control of Heliothis larvae which eat the flowers and green pods. Where cool, showery weather occurs at flowering, spraying with benlate may be required to control the fungal disease botrytis stem rot ( Botrytis cinerea ). In grazed situations neither disease is a problem. Powdery mildew ( Oidium sp.) turns mature leaves white towards the end of the growing season, but does not affect quality or acceptability. In South America anthracnose ( Colletotrichum gloeosporioides ) has been found on American jointvetch but not in Australia or Florida.

A. americana should be cut for hay or ploughed in for green manure at full flower. For cut-and-carry, the forage should be cut above 50 cm prior to flowering to encourage regrowth. Ripe seed remains on the plant so plants should be allowed to mature if commercial seed production is the aim. Ripe, dry seed will store and remain viable for many years.

Dry matter yields of 10-15 t/ha for a full season's growth have been recorded in Queensland. In Florida, cutting for hay, initially at 30 cm with a second cut at 90 cm, yielded 4.5 t/ha of quality hay per season. Five cuts between March and November produced 7.5 t/ha of hay in Puerto Rico. For seed production, direct header harvesting yielded up to 1000 kg/ha seed-in-pod in northern Queensland.

Collections are held at CIAT (Columbia); CENARGEN/EMBRAPA (Brasília, Brazil); ATFRGRC (CSIRO, Australia); University of Florida, Fort Pierce, Florida; IPB, University of the Philippines (the Philippines).

Most effort is directed at evaluating existing collections, but limited breeding work is being undertaken at the University of Florida to achieve nematode resistance and increased forage yield.

American jointvetch is a high yielding, high N fixing legume which tolerates waterlogging and is palatable to stock. Its role in South-East Asian areas will include green forage in pure stands or in mixed pastures, hay production, green manure, and ley pastures for rice paddies. It should be possible to select cultivars to suit climatic and growth habit requirements.

• Bishop, H.G., Ludke, D.H. & Rutherford, M.T., 1985. Glenn jointvetch: a new pasture legume for Queensland coastal areas. Queensland Agricultural Journal 111: 241-245.
• Bishop, H.G., Pengelly, B.C. & Ludke, D.H., 1988. Classification and description of a collection of the legume genus Aeschynomene. Tropical Grasslands 22: 160-175.
• Hodges, E.M., Kretschmer, A.E. Jr, Mislevy, P., Roush, R.D., Ruelke, O.C. & Synder, G.H., 1982. Production and utilisation of the tropical legume Aeschynomene. Circular S-290. Florida Agricultural Experimental Stations Institute of Foods and Agricultural Services. University of Florida, Gainesville. ll pp.
• Paul, W.R.C., 1951. Notes on legumes. 1. Tropical Agriculturalist 107: 15-20.
• Rudd, V.E., 1955. The American species of Aeschynomene. Contributions from the United States National Herbarium 32: 23-30.
• Rudd, V.E., 1959. The genus Aeschynomene in Malaysia (Leguminosae-Papilionatae). Reinwardtia 5: 23-36.
• Singh, R.G., 1971. Prospects of utilising wild legumes as green manure in a paddy - wheat rotation. The Allahabad Farmer 55: 489-495.
• Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 205-211.

H.G. Bishop