Desmodium uncinatum (PROSEA)
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Introduction |
Desmodium uncinatum (Jacq.) DC.
- Protologue: Prod. 2: 331 (1825).
- Family: Leguminosae
- Chromosome number: 2n= 22
Synonyms
Hedysarum uncinatum Jacq. (1798), Meibomia uncinata (Jacq.) Kuntze (1891).
Vernacular names
- Silverleaf desmodium, silverleaf Spanish clover (En)
- Indonesia: semanggi
- Philippines: pega-pega (Tagalog), koer (Bagobo)
- Thailand: enieo.
Origin and geographic distribution
Silverleaf desmodium is indigenous to the Americas, from northern Argentina to Mexico. Since first released as a pasture plant in 1962, it now occurs in isolated localities in the more humid regions of the subtropics and elevated tropics, including South-East Asia.
Uses
Silverleaf desmodium is used as a pasture legume in combination with a range of tropical pasture grasses. It can be made into hay.
Properties
Nitrogen concentrations in whole top growth have ranged from 1.9-3.7%, and N concentrations in the leaves were approximately double those of the stems. Tannin levels of 3.6% have been measured in the leaves.
Botany
Robust perennial herb with trailing stems to several metres long, ascending to about 1 m at flowering, densely covered with short hooked hairs, sticky to the touch. The stems form roots if in contact with moist soil and may scramble but not twine through the surrounding vegetation. Leaves with 3 leaflets; petiole up to 5 cm long; leaflets usually ovate, 2-10 cm × 1-4.5 cm, dark green with a characteristic narrow elliptical silvery shiny area about the midrib above, covered on both surfaces with ascending hairs. Inflorescence a terminal or axillary raceme up to 50 cm long, sometimes branching at lower floral nodes; flowers pink, 7-12 mm long, borne in pairs within the axils of caducous bracts. Pod 10-50 mm × 3-4 mm, curved, up to 12-articulate, covered with short hooked hairs and hence adhering to passing animals and clothing, slightly indented on the upper margin and deeply indented along the lower margin between the 5 mm long articles, breaking up at maturity.
Silverleaf desmodium is not vigorous in the seedling stage, but in warm conditions and in the absence of moisture stress, grows vigorously thereafter.
In the subtropics and elevated tropics, it flowers at the end of the wet season, earlier than Desmodium intortum (Miller) Urban. It is self-fertile, but flowers may require tripping.
The only cultivar of this species is "Silverleaf", released in Australia in 1962.
Taxonomically D. uncinatum belongs to a not well separated complex of species (including the closely related D. intortum ).
Ecology
Silverleaf desmodium requires an annual rainfall exceeding 1000 mm, well distributed through the growing season, and has some tolerance of flooding and shallow water tables. It grows at sea-level in the subtropics but favours elevations of 500-2000 m in the tropics. It has little tolerance of salinity or moisture stress during the growing season, but is more cold-tolerant than most other tropical pasture legumes. It will grow on a range of soils from sands to clay loams, but not heavy clays. It requires a soil of at least pH(H2O) 5.0, preferably 5.5. It will recover from moderate fires, but burning is not recommended.
Agronomy
Ideally, "Silverleaf" should be sown into a well-prepared seed-bed, but it has also successfully been sod-seeded into an existing pasture following treatment with a herbicide. It is normally sown with pasture grasses such as Setaria sphacelata (Schumach.) Stapf & Hubbard ex M.B. Moss. Seed should be inoculated with a special Bradyrhizobium strain to ensure effective nodulation. "Silverleaf" has a requirement for P, K, S and Mo, and these should be applied where they are naturally in short supply.
Several fungal diseases have been reported on "Silverleaf", but they have usually not restricted its production and persistence. Little leaf, caused by a mycoplasma-like organism also occurs, but usually only affects isolated plants. It is also susceptible to root-knot and other nematodes. In Australia, the most important pests are weevil larvae of Amnemus and Leptopius species, which damage or even sever taproots and larger adventitious roots, increasing its susceptibility to moisture stress.
Frequent cutting or grazing to < 10 cm will result in disappearance of the legume from a pasture. Even with appropriate grazing management and a suitable environment, "Silverleaf" may only persist for 3-10 years. Herbage is normally grazed. The species is not always particularly palatable to stock, which may take some time to get used to it.
Annual DM yields of 1.6-15 t/ha have been recorded from "Silverleaf" and "Silverleaf"/grass pastures. Studies have shown that nodulated "Silverleaf" in a grass/legume pasture can increase soil nitrogen by 90-160 kg/ha per year.
Genetic resources and breeding
Germplasm collections are held by ATFGRC (CSIRO, Australia) and CIAT (Colombia). There have been no breeding programmes with this species.
Prospects
Silverleaf desmodium has a restricted range of adaptation and will be further restricted by its inability to withstand sustained heavy grazing or cutting. However, within the limited areas and farm systems to which it is suited, it is a productive legume.
Literature
- Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London. pp. 350-354.
- Imrie, B.C., Jones, R.M. & Kerridge, P.C., 1983. Desmodium. In: Burt, R.L., Rotar, P.P., Walker, J.L. & Silvey, M.W. (Editors): The Role of Centrosema, Desmodium and Stylosanthes in improving tropical pastures. Westview Press, Boulder, Colorado, United States. pp. 97-140.
- Jones, R.M., 1989. Productivity and population dynamics of silverleaf desmodium (Desmodium uncinatum) and greenleaf desmodium (Desmodium intortum) and two D. intortum × D. sandwicense hybrids at two stocking rates in coastal south-east Queensland. Tropical Grasslands 23: 43-55.
- Lenné, J.M. & Stanton, J.M., 1990. Diseases of Desmodium species. Tropical Grasslands 24: 1-14.
- Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 286-296.
J.B. Hacker
