Desmodium incanum (PROSEA)
- Protologue: Prodr. 2: 332 (1825).
- Family: Leguminosae
- Chromosome number: 2n= 22
Hedysarum racemosum Aublet (1775), Aeschynomene spicata Poiret (1797), Desmodium canum Schinz & Thellung (1913, nom. illeg.).
- Kaimi, kaimi clover, creeping beggar weed (En). Pega-pega (Port).
Origin and geographic distribution
Originally from southern United States to Uruguay and Argentina, this species is now widely distributed in the wet tropics and some areas of the wet subtropics. It is abundant on volcanic soils in Hawaii, Fiji, Vanuatu and other Pacific Islands.
A potentially useful pasture species in mixed grass/legume pastures, especially under conditions of heavy grazing or low soil fertility. Reported to be a promising pasture species in Fiji and Vanuatu but not widely recommended elsewhere in the Pacific region.
Kaimi is not toxic to livestock, but palatability is reduced by tannins. Nitrogen concentrations of 2.0-2.5% have been reported.
Ascending to erect perennial herb or low shrub to 60 cm tall, rarely to 3 m, but in a grazed pasture situation it is typically prostrate and less than 20 cm tall. Stem trailing, fibrous to woody, sometimes beneath the soil surface, rooting readily at the nodes; root system deep, well-branched. Leaves trifoliolate, stipulate, petiolate; stipules at least partially connate abaxially, 3-11 mm × 1-3 mm, long persistent; petioles up to 3.5 cm long; leaflets very variable, mostly elliptical, terminal leaflets 2-9 cm × 1.5-4.5 cm, lateral ones up to 6 cm × 3 cm; leaflets on upper leaves tending to be narrower than those on lower leaves, dark green on the upper surface and often with a paler streak along the midrib, paler and densely pilose beneath. Inflorescence a terminal or axillary raceme, up to 20 cm long; flowers solitary or in fascicles of 3; pedicel 4-10 mm long; flower blue, red or purple, the standard up to 6 mm long. Pod up to 4 cm long, the upper margin straight, the lower strongly indented, covered with hooked hairs, with up to 8 articles of 3.5-5 mm × 2-3.5 mm. Seed oblongoid to kidney-shaped, 1 mm × 0.5 mm, light brown.
D. incanum is a very variable species and has been described many times; hence its nomenclature is quite complicated. The texture of the leaflets and the characters of the fruits are less variable.
Initial growth is slow, but later growth rates improve, provided moisture is adequate. Trailing stems begin to develop some 6 months after sowing. In regions with a pronounced seasonal climate, growth during the dry season is slow. At higher latitudes, flowering occurs when daylengths shorten. It is naturally spread by animals and humans, the hooked hairs on the pod adhering to fur or clothing.
D. incanum grows best in regions with annual rainfall of 1500-3000 mm, but will persist and spread in areas receiving 1000 mm. Optimum temperatures are reported to be 30°/25 °C during the growing season. The species is tolerant of light frosts and temporary flooding. In regions where it is naturalized, it is particularly common along roadsides, wasteland and other disturbed ground. D. incanum is apparently best adapted to fertile, neutral to slightly alkaline soils, but may be grown on a wide range of soil types from sands to light clays, pH 4.0-8.0.
D. incanum is propagated by seed. Seed is often hard and may require treatment with concentrated sulphuric acid for 10 minutes before sowing. It is recommended that the seed be inoculated with the special Desmodium strain of Bradyrhizobium . It requires a well-prepared seed-bed for the most reliable establishment but may also be broadcast into an existing pasture. Recommended sowing rate is 5 kg/ha at ca. 5 mm depth. It responds to lime and P, but these are not normally considered essential. It grows with a range of pasture grasses, but is usually associated with stoloniferous or rhizomatous species.
D. incanum is reported to be sensitive to Peanut Mottle Virus and may act as a source for this virus for cultivated groundnuts in the United States. Several fungal diseases have been recorded on D. incanum , as well as little leaf and desmodium mosaic virus, but they rarely cause serious problems. Seedlings may be damaged by cutworms, and in Hawaii the rose beetle and the cyst nematode Heterodera trifolii may cause damage.
The stoloniferous habit of this species enables it to withstand heavy grazing. A 30-40 day rest period between grazings has been recommended, but the species can persist under close continuous grazing. It is amongst the more persistent legume species under heavy grazing. D. incanum can yield up to 6500 kg/ha of DM but is normally considered to be low-yielding. Seed yields may exceed 200 kg/ha, but lower yields are more usual. Under lenient defoliation, and particularly with high P input, it is reported to be lower-yielding and to fix less N than the more widely grown D. intortum (Miller) Urban.
Genetic resources and breeding
No cultivars are available. Collections are maintained at ATFGRC (CSIRO, Australia), EMBRAPA (Brazil), CIAT (Colombia), and USDA (Fort Pierce, Florida, United States). D. incanum is self-fertile, but some outcrossing is believed to occur. It has been hybridized with D. uncinatum (Jacq.) DC., but the hybrid is sterile.
D. incanum is a species which could warrant further investigation for South-East Asian pastures since it tolerates heavy grazing or cutting. Early results from Hawaii were extremely promising, but interest in the species has not been maintained.
- Cameron, D.G., Jones, R.M., Wilson, C.P.M., Bishop, H.G., Cook, B.G., Lee, C.R. & Lowe, K.F., 1989. Legumes for heavy grazing in coastal subtropical Australia. Tropical Grasslands 23: 153-161.
- 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.
- Lenné, J.M. & Stanton, J.M., 1990. Diseases of Desmodium spp. - a review. Tropical Grasslands 24: 1-14.
- Nicolsen, D.H., 1978. Illegitimate "basionyms", impact on priority and author citation or, the rise of Desmodium incanum and fall of D. canum (Fabaceae). Taxon 27(4): 365-370.
- Schubert, B.G., 1980. Desmodium. In: Dwyer, J.D. (Editor): Flora of Panama. Part 5: Family 83, Leguminosae subfamily Papilionoideae. Annals of the Missouri Botanical Garden 67: 640-643.
- Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 263-267.