Canavalia ensiformis (L.) DC commonly known as jackbean is a legume native to Central and South America from Mexico south to Brazil and Peru, and to the West Indies. The earliest known record of its existence is from about 900 ad., from Oaxaca in central Mexico. It is cultivated on a small scale throughout the tropics, but is of relatively little economic importance in world trade).
C. ensiformis is an annual plant, growing bushy and erect from 0.6-1.6 m in height, becoming woody with age. It can also grow as a climber, especially if shaded. Branches are normally found singly at the lower nodes. However, as many as three can develop at one node. Leaves arise alternately and are trifoliate. Leaflets, commonly up to 12 cm long, are ovate-elliptic. The center leaflet is slightly elongated. Petioles are as long as the leaflets. The flowers are typically papillionaceous, rose to purple in color, rounded, about 2 cm long; up to 20 may develop in groups of 2-3 on each peduncle. Pods are linear, slightly curved, and commonly 30 x 2.5 cm in size. Seeds are white or ivory with a brownish mark near the grayish hilum, about 2.1 x 1.5 x 1 cm in size; 12-20 develop in each pod.
The jackbean has been more or less employed as feed for domestic animals, but both the herbage and seeds are eaten with reluctance by most animals. The dry mature seeds are used as foodstuff, but are not popular because of their unacceptable flavor and texture. The jackbean is presently cultivated throughout the tropics as a cover crop, a soil cover for erosion control, and forage for ruminants. As a green manure, it is intercropped with cacao, coffee, and sugarcane. Young pods and immature seeds are used as vegetables. Flowers and young leaves are steamed as a condiment, in Indonesia. Roasted beans are sometimes used as a substitute for or filler in coffee.
Table Jackbean seed yields
The plant is reported to tolerate disease, drought, fungus, insects, low pH, salts, sand shade, slope virus, and waterlogging. Seed yield reports vary considerably (Table Jackbean seed yields). However, this may be the result of different growing conditions. High yields in Puerto Rico and Venezuela were obtained under experimental conditions. In the case of the lowest yields, not enough information on the environmental conditions was reported, but these yields may have resulted from restricted rainfall conditions. Nevertheless, the figures show the survival potential of the jackbean. This is more evident when compared with other crops. Herrera reported a jackbean seed yield in Yucatan of 1800 kg/ha, whereas average yields for maize and the common bean under similar conditions were 600 and 1500 kg/ha, respectively. This was carried out in an area too rocky for mechanization, where the range of crops was already limited by the alkaline soil and the tropical environment. Additionally, the jackbean being a legume with a nitrogen-fixing ability, it would not be expected to need fertilizer nitrogen. However, to what extent this is correct is not yet clear. In a review of the nitrogen-fixing ability of 13 species of pulse, legumes, the jackbean was recorded as having the lowest value.
In contrast with the soybean, the jackbean forms seeds which accumulate starch rather than lipids. Its carbohydrates can be efficiently used by ruminants and poultry, therefore it is a good source of energy. The seed is also a good source of minerals with a high phosphorus content (3.5 g/kg dry wt.). The protein content is high, i.e., 24-31%. The amino-acid composition is very similar to that of the soybean seed, although it has a lesser lysine content, and similar to other legumes, is poor in amino acids containing sulfur. Molina et al. reported a product extracted from jackbean seed which was rich in protein and starch, with a high nutritive value.
Since the jackbean has a high protein content in seeds and foliage, high seed yields without substantial management inputs, and probably grows in soil independent of nitrogen, the plant has been identified by the United States National Academy of Sciences (NAS 1979) as a potential food source for the tropics, which could help agricultural production in developing countries.
Canavalia ensiformis: Conclusions and Prospects
Jackbean is a legume with potential, but its usefulness as animal feed (and eventually for human nutrition) is so far restricted to ruminants. Jackbean toxicity, in particular the heat-labile fraction, is an obstacle which should be overcome in order to extend its use. So far this has not been possible by means of processing the seeds already formed. Although such efforts should continue, this task seems to be more feasible to be solved through genetic improvement. The evidence supports that L-canavanine is responsible for seed toxicity after heat processing, therefore, genetic improvement must be aimed at reducing the content of L-canavanine in the plant. However, it is important to demonstrate without any doubt that this amino acid is the cause of this residual toxicity, since other heat-stable constituents could contribute to the problem; for instance, the nitrate content of the seed is high (15 g/kg). This problem could be approached by testing the effect of L-canavanine added to standard diets in economically important animals, such as chicks. We also need to extend our understanding of the importance of L-canavanine in plants.
Selections from the book: “Medicinal and Aromatic Plants IV”, 1993.