Indigofera hendecaphylla (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Indigofera hendecaphylla Jacq.

Protologue: Collectanea 2: 358 (1789).

Family: Leguminosae - Papilionoideae

Chromosome number: 2n= 16 (diploid), 32 (tetraploid)

Synonyms

• Indigofera celebica Miquel (1855),
• I. siamensis Hoss. (1907),
• I. spicata Forssk. sensu auct. mult.

Note: I. hendecaphylla is often misspelled I. endecaphylla.

Vernacular names

• Creeping indigo (En). Trailing indigo (Am).
• Indigotier rampant (Fr)
• Indonesia: basingan, sibar (Sumatra), baleh angin (Sulawesi)
• Thailand: khram-khrua (northern)
• Vietnam: chàm bụi.

Origin and geographic distribution

I. hendecaphylla occurs naturally in Africa, Madagascar, throughout South and South-East Asia and in Papua New Guinea. It was taken into cultivation in Java and Peninsular Malaysia in 1923 from Sri Lanka. Cultivation spread from Java to the Philippines in 1927. I. hendecaphylla has been grown experimentally in Australia and has become naturalized in northern Queensland. Later, it was brought to the Americas, where it is widely cultivated in Hawaii, Jamaica, Puerto Rico, and Florida.

Uses

I. hendecaphylla provides a good soil cover and smothers weeds. In tea estates in Sri Lanka I. hendecaphylla was the most popular green manure and cover crop. In Indonesia and Peninsular Malaysia it is used as a cover crop in rubber, sisal, oil palm and tea plantations; in Africa in coffee plantations. Some strains of I. hendecaphylla, especially those from Africa, provide valuable and palatable fodder, but the leaves and seeds of other strains are highly hepatotoxic.

Properties

Tests in Sri Lanka and Indonesia indicate that green material contains per 100 g dry matter: organic matter 87.4 g, ash 12.6 g, N 3.1 g, P 0.2 g, K 1.3 g, Ca 2.6 g. Analysis of the leaves and stems used for fodder gave the following values per 100 g dry matter: protein 20.5 g, fat 3.0 g, soluble carbohydrates 39.5 g, fibre 23.5 g, ash 11.0 g; the digestibility of the components was: protein 76%, fat 67%, soluble carbohydrates 81%, fibre 60%.

The leaves of I. hendecaphylla, possibly only of tetraploid forms originally from Sri Lanka, contain per 100 g dry matter 0.1-0.5 g indospicine (2,7-diamino-7-amino-heptanoic acid) while the seeds contain 0.1-2 g. Indospicine is a specific antagonist of arginine, interfering with its synthesis and incorporation into proteins and with the synthesis of DNA. Indospicine is highly toxic to chicken, rabbits, pigs, goats, sheep, cattle and horses. In small doses it causes loss of vitality and abortion in cattle and goats. Indospicine is especially dangerous to horses, which relish plants containing it and eat them preferentially. I. hendecaphylla also contains nitrogenous compounds called endecaphyllins, as well as 3-nitropropionic acid.

The weight of 1000 seeds is about 20 g.

Description

• Sub-erect shrublet (20-)40-75 cm tall, gradually becoming prostrate. Main root 50-100 cm × 0.5-1 cm, white. Stem creeping, up to 2 m long, rooting at the nodes, pale green to yellow, tough; branches ascending, striate, with appressed, biramous hairs with equally long arms.
• Leaves pinnate, alternate, 3-5 cm long; stipules narrowly triangular, apex caudate, 5-6 mm × 1.5-2.0 mm; petiole 1-3 mm long; leaflets 9-11, shortly petioluled, alternate, sometimes almost opposite, narrowly oblong-elliptical to narrowly oblanceolate, 3-20 mm × 2-9 mm, apex rounded, mucronate, upper surface subglabrous.
• Inflorescence an axillary raceme, 5-17(-23) cm long; flowers 4-6 mm long, crowded, brick red to pink, occasionally purple or white; pedicel about 1 mm long; calyx tube 1.5 mm × 1.5 mm, teeth narrowly triangular, 2.5-3 mm long; standard broadly ovate 4.0-5.5 mm × 3.0-4.0 mm, strigose on the back; wings 3.0-4.5 mm × 1.5-2.0 mm, glabrous, margins long-ciliate along the upper auricle; keel 3.5-5.0 mm × 2.0-2.5 mm, hairy, margin ciliate, lateral pocket 1 mm long; staminal tube 4-5 mm long, apex rounded to obtuse, anthers 0.5 mm × 0.5 mm; ovary glabrous.
• Fruit a descending, straight, needle-like, dark brown pod, stiff, somewhat quadrangular to round in cross-section, 2.0-3.5 cm × 2-2.5 mm, 5-10-seeded, beak 2 mm long, endocarp not blotched.
• Seed very small, cubic to quadrangular-ellipsoid, 2 mm × 1 mm, yellowish to dark brown.

Growth and development

Seedlings develop a strong taproot which assists in loosening the soil. When cuttings are used for planting I. hendecaphylla remains very low, the cover rarely exceeding 12 cm in height. A fair cover can be formed in 6 months and a continuous even cover in a year from planting. The plants send out trailing stems which, under favourable conditions, may attain a length of 2 m, producing numerous adventitious roots at the nodes. As the plants mature they become taller and at 2 years of age they are usually about 30-40 cm tall. Vigorous regrowth occurs at the start of the rainy season.

Other botanical information

I. hendecaphylla and I. spicata Forssk. used to be considered as the same species and were then named I. spicata. They are now considered to be different species. The literature is therefore confusing, and references to toxicity most probably refer to I. hendecaphylla. In I. hendecaphylla the staminal tube is 4-5 mm long, distinctly longer than the calyx, the apex of the keel rounded to obtuse, and leaves have 9-11, narrowly oblong-elliptical to narrowly oblanceolate leaflets. In I. spicata the staminal tube is 3-3.5 mm long, not exceeding the calyx, the keel apex acute, while the leaves have 5-8 obovate leaflets with cuneate base. I. spicata is restricted to Africa and Yemen, often in the drier regions. I. hendecaphylla occurs pantropically, often in more humid areas; it is a very variable species and many varieties have been described, distinguished by leaflet form and hairiness. These distinctions are not considered useful, because many intermediate forms occur.

Ecology

I. hendecaphylla thrives from 0-700 m altitude and is found to about 2500 m. It requires an average annual temperature of 16-27 °C and an annual rainfall of 600-1500 mm, but may be found in wetter locations receiving up to 4000 mm annual rainfall. In cultivation it is fairly resistant to drought and shade. Under heavy shade, as in old rubber plantations, growth is poor. I. hendecaphylla performs best on clay soils, but grows on various soil types, including sandy soils, with a pH of 5.0-7.7. It is tolerant of poor, moderately acid, P-deficient soils. Soil covers of I. hendecaphylla are notorious for harbouring snakes and leeches.

Propagation

I. hendecaphylla can be propagated by seed and by stem cuttings. Seed is very hard and germinates poorly without scarification. Mechanical scarification and treatment with sulphuric acid for 40-60 minutes can increase the germination rate to about 80%. To obtain a good distribution of the seed it is mixed with sand or filtered dry soil at a ratio of seed to sand of 1 : 4 before sowing. If planted in rows 60 cm apart the seed rate is about 3.3 kg/ha. Cuttings are used when seed is difficult to obtain. For large-scale plantings, they should be raised in nurseries. Cuttings of about 20 cm long are planted at a spacing of 60 cm × 60 cm with 5 cuttings per hole. Once established, I. hendecaphylla is self-sowing.

Husbandry

The maximum effect of I. hendecaphylla as a green manure is reached when the cover crop is incorporated in the soil when still green and flowering has started. Green manure crops produce 4.5-25 t/ha of green material. In trials in Indonesia I. hendecaphylla has produced a green matter yield of 3.0 t/ha 3 months after planting, containing 10 kg nitrogen and 3 kg phosphorus. After 6 months the green matter yield was 18 t/ha, containing 86 kg nitrogen and 21 kg phosphorus.

A cover crop of I. hendecaphylla controls erosion effectively on hilly and undulating land even under heavy rainfall, and is considered more effective than Clitoria ternatea L. Few weeds, except some grasses, can grow through this cover and, once established, a reduction in weeding costs may be anticipated. Weeds such as Mikania spp. and Convolvulus spp. can cause some trouble.

When ring-weeding around young tea plants the stems of I. hendecaphylla have to be cut, as these are otherwise difficult to incorporate into the soil.

Diseases and pests

I. hendecaphylla is remarkably free from diseases. The only important pest in Sri Lanka is the caterpillar Dichomeris ianthes, which sometimes completely defoliates the crop; however, it normally recovers very quickly. In Peninsular Malaysia, the plant is liable to attacks by the larvae of a small moth, probably Lamprosema diemenalis, but the damage is not permanent.

Genetic resources and breeding

A germplasm collection of Indigofera L. is being maintained at the Southern Regional Plant Introduction Station of the United States Department of Agriculture, Griffin, Georgia containing a few accessions of I. hendecaphylla. Strains with a reduced indospicine content have been bred in Australia, but indospicine-free material has not yet been obtained.

Prospects

I. hendecaphylla remains an excellent cover crop, providing a dense, well-rooted, low cover in humid areas. In drier areas growth is too slow. More research is needed on the variation in indospicine content, its relation with polyploidy and its presence in African material. Strains from Africa that have been used as fodder crop may be developed into cover crops safe for farm animals.

Literature

• Aylward, J.H., Court, R.D., Haydock, K.P., Strickland, R.W. & Hegarty, M.P., 1987. Indigofera species with agronomic potential in the tropics. Rat toxicity studies. Australian Journal of Agricultural Research 38: 177-186.
• de Kort, I. & Thijsse, G., 1984. A revision of Indigofera in South-East Asia. Blumea 30: 89-134, in particular 132-134.
• Duke, J.A., 1981. Handbook of legumes of world economic importance. Plenum Press, New York, United States. pp. 98-99.
• du Puy, D.J., Labat, J.-N. & Schrire, B.D., 1993. The separation of two previously confused species in the Indigofera spicata complex (Leguminosae: Papilionoideae). Kew Bulletin 48: 727-733.
• Morton, J.F., 1989. Creeping indigo (Indigofera spicata Forssk.) (Fabaceae) - hazard to herbivores in Florida. Economic Botany 43(3): 314-327.
• Smolenski, S.J., Kinghorn, A.D. & Balandrin, M.F., 1981. Toxic constituents of legume forage plants. Economic Botany 35(3): 321-355.

Authors

• B. Sunarno