Desmodium heterophyllum (PROSEA)
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Introduction |
Desmodium heterophyllum (Willd.) DC.
- Protologue: Prodr. 2: 334 (1825).
- Family: Leguminosae
- Chromosome number: 2n= 22
Synonyms
Hedysarum heterophyllum Willd. (1802), Meibomia heterophylla (Willd.) Kuntze (1891).
Vernacular names
- Hetero, Spanish clover (En)
- Indonesia: sisik betok (Indonesian), heuheulangan (Sundanese), sukut jareman (Javanese)
- Malaysia: rumput sisek naga, rumput sisek betok, rumput telinga tikus
- Cambodia: trôm' préi, smau 'âm'bôk
- Laos: padông môd liinz
- Thailand: ya-maengmi (northeast)
- Vietnam: ha[n] the, tràng qu'a di diêp (southern).
Origin and geographic distribution
Hetero is native to tropical Asia and adjacent islands, occurring naturally in Mauritius, India, Nepal, Sri Lanka, Burma, Thailand, Indo-China, Malesia, China and Taiwan. It is adventive to the South Pacific and naturalized in parts of north-eastern Australia.
Uses
Hetero is primarily used as a legume for heavily grazed pastures in the wet tropics, and is recommended as such in Malaysia. It is also used as a cover crop e.g. in pepper gardens in Sarawak. It is not suitable for cut-and-carry systems.
Properties
Nitrogen concentration in new growth of hetero is about 2.8-3.0%. When grown in mixtures with pangola grass ( Digitaria eriantha Steudel) it increased the N concentration of the grass from 0.86% to 1.12%.
Botany
A prostrate or ascending perennial undershrub, with woody rootstock. Stems up to 1.5 m long, freely branching and covered with spreading reddish-brown hairs. Leaves trifoliolate, on lower parts often unifoliolate; petiole 5-15 mm long; leaflets obovate or elliptical, usually 10-25 mm × 8-14 mm, laterals smaller than the terminals, rounded or indented at the tip, hairless on the upper surface, sparsely covered with long hairs on the lower surface. Inflorescence a few-flowered axillary or terminal raceme to 6 cm long, and/or leaf-opposed clusters of 1-3 flowers; pedicel 10-25 mm long; flower about 5 mm long, purple or white. Pod narrowly oblong, 10-20 mm × 3-5 mm with 3-6 broadly oblong or quadrate articles 3-4 mm long, densely covered with minute hooked hairs, the isthmus between the articles ca. ¾ the width of the pod, dehiscing along the lower margins when ripe. Seed transversely elliptical, about 1.5 mm × 2 mm. Hetero is self-compatible but normally cross-pollinated. Cultivar "Johnstone" was released in Australia in 1973.
Ecology
Hetero is adapted to the humid tropics with annual rainfall exceeding 1500 mm, and to a wide range of soils from sands to clays. It is reported to be less tolerant of soil acidity than D. heterocarpon (L.) DC. It is intolerant of fire and salinity, and susceptible to frost.
Agronomy
Seed production of hetero is not easy, owing to poor synchrony within the crop (associated with the indeterminate nature of the plant and the two inflorescence types) and the fragility of ripe pods which are carried within or close to the upper levels of the herbage. Therefore, it is commonly established vegetatively by cuttings. However, because hetero requires a specific strain of Bradyrhizobium , it is preferable to plant out sods which contain vegetative material, seed and Bradyrhizobium . Fresh seed has some hard-seededness, which may be broken by scarification. Seed should be sown no deeper than 5 mm and should be inoculated with the appropriate Bradyrhizobium , if possible. Early growth has been noted as slightly unpalatable, but this is an advantage as it promotes successful establishment.
Hetero occurs as a component of native pastures in parts of Indonesia and Fiji, where its poor productivity as a naturally occurring species can be improved by applying P fertilizer. Unlike most tropical pasture legumes, hetero tolerates heavy grazing. It has an excellent ability to spread naturally, both by means of its freely-branching stolons and its free-seeding habit, and competes well against low-growing weeds. Reports on its tolerance to shade are confusing, but recent experience suggests that, when adequately fertilized, it is one of the most shade-tolerant of the pasture legumes.
Hetero is sensitive to cercospora leaf-spot (Cercospora sp.) and to foliar blight (Rhizoctonia solani), which is frequent in humid regions of the tropical American lowlands. Wilt (Sclerotium rolfsii) has caused seedling mortality in greenhouse tests and little leaf (mycoplasma-like organisms) has caused damage, but these diseases are considered to be unimportant under grazing. Root-knot nematodes (Meloidogyne arenaria, M. incognita) can also cause damage.
Since hetero can withstand heavy grazing, it has the ability to persist in mixtures with vigorous creeping grasses where twining and shrubby legumes would be grazed out. However, persistence has been poor on soils of poor fertility, particularly those deficient in trace elements, and in ungrazed or lightly grazed stands with tall-growing grasses such as guinea grass ( Panicum maximum Jacq.). Cattle grazing north-eastern Australian pastures based on hetero and either Digitaria eriantha or Brachiaria decumbens Stapf had liveweight gains of over 750 kg/ha per year.
Genetic resources and breeding
Collections of D. heterophyllum are held by ATFGRC (CSIRO, Australia) and CIAT (Colombia). No breeding has been carried out in this species.
Prospects
The relatively unusual ability of hetero to withstand and spread under heavy grazing and its tolerance of shade suggests that it is likely to be more widely used in the humid tropics.
Literature
- Bogdan, A.V., 1977. Tropical pasture and fodder plants. Longman, London. pp. 343-344.
- Halim, R.A. (Editor), 1989. Grassland and forage production in South-east Asia. Proceedings of first meeting of the regional working group on grazing and feed resources of South-east Asia, 27 Feb - 3 Mar, 1989. FAO, Rome. 216 pp.
- Knaap-van Meeuwen, M.S., 1962. Preliminary revisions of some genera of Malaysian Papilionaceae 5. - A census of the genus Desmodium. Reinwardtia 6: 251-252.
- Lenné, J.M. & Stanton, J.M., 1990. Diseases of Desmodium species. Tropical Grasslands 24: 1-14.
- Ohashi, H., 1973. The Asiatic species of Desmodium and its allied genera (Leguminosae). Ginkgoana 1: 239-241.
- Partridge, I.J., 1986. Effect of stocking rate and superphosphate level on oversown fire climax grassland of mission grass (Pennisetum polystachion) in Fiji. Tropical Grasslands 20: 166-173.
- Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 271-274.
Authors
J.B. Hacker & J.K. Teitzel
