Desmanthus virgatus (PROSEA)
Desmanthus virgatus (L.) Willd.
- Protologue: Sp. Pl. ed. 4, Vol. 4(2): 1047 (1806).
- Family: Leguminosae
- Chromosome number: 2n= 28
Mimosa virgata L. (1753).
- False tamarind (En). Acacia courant, acacia savane (Caribbean) (Fr)
- Thailand: thua desmanthus
- Vietnam: cây diê[n] keo.
Origin and geographic distribution
D. virgatus originated in the Americas where it is widespread, occurring from Arizona, Florida and Texas in the United States, throughout much of Mexico and has been recorded in most countries south to Argentina as well as in the Caribbean and the Galapagos Islands. The main centre of diversity of the genus is Mexico and that is probably true of D. virgatus as well. The species is naturalized in some regions of the tropics including the island of Sulawesi (Indonesia) and in the Pacific islands (New Caledonia).
At present D. virgatus is not yet sown on farms in South-East Asia despite recent promising results from species evaluation experiments. In the Americas it makes a contribution to native pastures but is not yet developed to the point of commercial release. In India it is used in hedges to provide cut forage, and is being evaluated in Australia as a species for permanent pastures.
In some areas the species has become a weed.
Nitrogen concentrations of 3.6% in the leaves and of 1.1% in the stems have been measured.
There are 170-340 seeds/g.
A perennial or sometimes annual shrub or herb, prostrate to erect, 0.5-3 m tall, taprooted (the taproot develops into a storage organ in some forms); stem unbranched or sparingly branched, hollow, subglabrous, ridged. Leaves bipinnate, 2-8 cm long, with 1-7 pairs of pinnae, usually with a petiolar gland between the lowest pair of pinnae; petiole up to 5 cm long; pinnae up to 7 cm long with 10-25 pairs of leaflets; leaflets linear to linear-oblong, 4-9 mm × 1-2 mm, oblique and eccentric at the base, obtuse to apiculate at the apex; stipules linear-subulate, up to 6 mm long. Inflorescence a small globose 6-10-flowered head; peduncle up to 7.5 cm long; flowers bisexual or with some neuter lower flowers; petal white to cream, ca. 4 mm long, sometimes absent; stamens 10. Fruit linear to falcate, 3-10 cm × 3-4 mm, dehiscing with 2 valves, smooth or subseptate, red-brown, shiny, 20-30-seeded. Seed ovoid to ellipsoid, ca. 2 mm long, glossy brown.
D. virgatus is extremely variable in habit and in other characters such as pod shape and size and leaf morphology. Four varieties are recognized by Isely: var. virgatus, var. glandulosus Turner, var. depressus (Humb. & Bonpl. ex Willd.) B. Turner and var. acuminatus (Benth.) Isely. These are separated by habit, leaf characteristics, and the number and location of glands on the petiole and leaf. Most accessions belong to var. virgatus.
D. virgatus is a copious seed producer with many forms acting as annuals if not cut or grazed.
D. virgatus is adapted to a wide range of tropical and subtropical environments. It has been collected at sites in the Americas with annual rainfall ranging from 250-2000 mm and altitudes from sea-level to 2000 m. Most commonly the species is associated with neutral to alkaline clay or clay-loam soils. Crowns survive frosting but top growth is frost-sensitive.
Propagation is by seed. Seed usually has a high proportion of hard seed and hard-seededness can be broken by mechanical scarification or hot water treatment. Seeding rates of between 2-6 kg/ha should be adequate. D. virgatus should preferably be inoculated prior to sowing by a specific strain of Bradyrhizobium . It is adapted to defoliation and should have cutting or grazing applied soon after establishment to induce branching and crown development. DM yields of 7.6 t/ha have been obtained in Fiji, and fresh material yields of 23 t/ha (Hawaii) and 70 t/ha (Australia) have also been reported.
Genetic resources and breeding
D. virgatus germplasm is available from the ATFGRC (CSIRO, Australia) and from CIAT (Colombia). No breeding programmes are in progress. The extreme natural variation in climatic origin, plant morphology and flowering time of the species has enabled the selection of accessions for advanced evaluation from wild collections.
Three cultivars have recently been released in Queensland, Australia. They differ mainly in their time of flowering in the subtropics and higher latitude tropics. Cultivar "Marc" is early flowering, "Bayamo" is mid-flowering and "Yuman" is late flowering. "Marc" has a lower yield potential but is more likely to persist in grazed pastures in the long term. The existence of adventive populations in Sulawesi (Indonesia) and in the Pacific shows that the species has potential as a forage in Asia especially on neutral to alkaline soils. There is also interest in the species as a forage legume for upland intercropping. The wide range of material available should enable the development of commercial material for the region.
- Isely, D., 1970. Legumes of the United States: 2. Desmanthus and Neptunia. Iowa State Journal of Science 44: 495-511.
- Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 548-550.
- Topark-Ngarm, A., Armada, E.C., Tengco, P.L. & Carangal, V.R., 1990. Food and forage intercropping under upland condition. In: Proceedings of the Crop-Animal Systems Research Workshop, Serdang, Malaysia, August 15-19, 1988. MARDI/IDRC/ARFSN. pp. 453-471.
- Turner, B.L., 1950. Texan species of Desmanthus (Leguminosae). Field and Laboratory 18: 54-65.
- Turner, B.L., 1950. Mexican species of Desmanthus (Leguminosae). Field and Laboratory 18: 119-130.
B.C. Pengelly & A. Topark-Ngarm