Chamaecrista rotundifolia (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Chamaecrista rotundifolia (Persoon) Greene

Protologue: Pittonia 4: 31 (1899).

Family: Leguminosae

Chromosome number: 2n= 16

Synonyms

Cassia rotundifolia Persoon (1805).

Vernacular names

• Roundleaf cassia, round-leafed cassia (En)
• Vietnam: muôn'g lá tròn.

Origin and geographic distribution

Roundleaf cassia is native to an area extending from Mexico through Brazil and Uruguay, including the Caribbean region. It has been introduced and naturalized in the southern United States and in parts of West Africa. It has been introduced in Australia and is used commercially.

Uses

Roundleaf cassia is only used for grazing, although good silage has been obtained experimentally.

Properties

Preliminary data indicate that nutrient levels in cassia are average for tropical legumes, with N concentrations of 1-3%. Although some species of Cassia are toxic, 6 accessions of roundleaf cassia have been fed to rats and there were no symptoms of toxicity. The live weight gains and intake of rats fed with roundleaf cassia have been found to be marginally better than with rats fed lucerne. Cultivar "Wynn" was also found to be free of toxic compounds in studies with pen-feed sheep. There are 200-500 seeds/g.

Botany

An annual or weak perennial semi-erect to prostrate herb, in age basally suffrutescent, with woody-fibrous blackish taproot up to 1 cm in diameter; stems up to 1 m long, not rooting at nodes. Leaves ascending, bifoliolate, petiole up to 1 cm long; leaflets subrotund to broadly obovate, 0.5-5 cm long, by day ascending, face upward from tip of petiole, folded face-to-face at night, venation slightly prominent on both surfaces; petiolule only a thickened pulvinule, without a gland. Flowers in racemose axillary clusters of 1-3; pedicel up to 6 cm long; sepals 5, greenish or reddish-brown, 3-13 mm long; petals 5, yellow, as long as or slightly longer than sepals. Pod linear-oblongoid, straight or slightly curved, (1.5-)2-5.5(-6) cm × 0.3-0.5(-0.6) cm, blackish-brown when ripe, dehiscent. Seed rectangular in outline, flattened, 2-3 mm long.

The species is quite variable in its stature, pubescence and size of flower parts and leaves, allowing distinction of many ecotypes. Provisionally (until better studied), only two varieties have been distinguished by Irwin & Barneby based on size and proportion of the flowers alone:

• var. rotundifolia : flowers small, the largest petal up to 7 mm long, the longest fertile anther up to 4.4 mm, the style up to 2 mm long. Range: from Florida (United States) and Sinaloa (Mexico) to Argentina. Synonyms: Cassia bifoliolata DC. ex Colladon (1816), C. fabaginifolia Kunth (1824), C. monophylla Vellozo (1825).

• var. grandiflora (Bentham) Irwin & Barneby: flowers larger, the longest petal up to 17 mm, the largest fertile anther up to 11.5 mm, the style up to 8.5 mm long. Range: more local within that of var. rotundifolia , but never associated with it. Synonym: Cassia bauhiniifolia Kunth (1819).

Growth is indeterminate and will continue after flowering for as long as temperatures and moisture conditions are suitable.

One cultivar, "Wynn" (belonging to the var. rotundifolia ), has been released in Australia. It can seed freely throughout the growing season, but primarily in autumn. Other lines flower much later and, in areas with a reliable and longer growing season, are higher yielding.

Ecology

Roundleaf cassia is best suited to areas receiving from 700-1400 mm rainfall in the seasonally dry tropics and subtropics. It is not suited to poorly drained sites or heavy textured soils, and is very intolerant of waterlogging. It grows best on free-draining, friable sandy soils. Top growth is readily killed by frost.

Agronomy

Seed germination should be checked before sowing to ensure that hard-seededness is not excessive. Seed can be broadcast into closely grazed pastures, but establishment is more reliable with some form of soil disturbance. Seeding rates of 2-4 kg/ha are recommended, but lower rates can be used especially if sown in a mixture with legumes. It nodulates readily with native cowpea rhizobia and there are no records of failure to nodulate. Long-term persistence is assisted by regular recruitment from soil seed reserves, which are frequently 3000/m²and can be as high as 15 000/m².

No serious disease or pest problems have been recorded although the species is a known host of several viral and fungal diseases.

To date, roundleaf cassia has only been used for grazing, where it has proved to be persistent under a wide range of grazing pressure, although persistence and productivity are poorer with vigorous grasses and also at light grazing pressures. In mixed cassia/grass pastures, cattle tend to selectively graze the grass at the beginning and middle of the growing season, and the percentage of cassia in the diet increases at the end of the growing season. Seed pods are eaten by cattle, and peak levels of 1-3 seeds per g of dry cattle faeces aid in the natural spread of the species. Roundleaf cassia can give DM yields of over 5 t/ha in pure swards, but annual yields are lower in grass/legume pastures. Seed yields can range from 200-800 kg/ha. Roundleaf cassia is suited to either direct heading or hand harvesting of seed.

Genetic resources and breeding

The largest germplasm collection is held at ATFGRC (CSIRO, Australia). The main variation is in the time of flowering and growth habit.

Prospects

Within its adaptation limits of rainfall and soil type, roundleaf cassia shows considerable promise. It may provide an alternative legume in some of the areas suitable to shrubby stylo ( Stylosanthes scabra Vogel). New cultivars of mid- and late-season maturity, as compared to the early-flowering "Wynn", will be required to exploit its full potential.

Literature

• Ahn, J.H., Elliot, R. & Minson, D.J., 1988. Quality assessment of the fodder legume Cassia rotundifolia. Tropical Grasslands 22: 63-67.
• Cook, B.G., 1988. Persistent new legumes for heavy grazing 2. Wynn round-leafed cassia. Queensland Agricultural Journal 114: 119-121.
• Irwin, H.S. & Barneby, R.C., 1982. The American Cassiinae. Memoirs of the New York Botanical Garden 35(2): 727-733.
• Lenée, J.M., 1990. Diseases of Cassia species - a review. Tropical Grasslands 24: 311-324.
• Oram, R.N., 1990. Register of Australian herbage plant cultivars. CSIRO, Australia. p. 284.
• Skerman, P.J., Cameron, D.G. & Riveros, F., 1988. Tropical forage legumes. FAO, Rome. pp. 232-236.
• Strickland, R.W., Greenfield, R.G., Wilson, G.P.M. & Harvey, G.L., 1985. Morphological and agronomic attributes of Cassia rotundifolia Pers., C. pilosa L. and C. trichopoda Benth., potential forage legumes for northern Australia. Australian Journal of Experimental Agriculture 25: 100-108.

Authors

R.M. Jones