Canavalia is a genus of approximately 73 species of tropical climbing vines in the legume family (Fabaceae), order Fabales. Commonly known as jack-beans, members of this genus share a pantropical distribution, occurring across tropical regions of Africa, Asia, the Pacific, and the Americas.
Plants in this genus are typically twining vines with trifoliate leaves and showy pea-type flowers, usually pink to purple, that are pollinated by solitary bees and carpenter bees including Xylocopa confusa. The genus is notable both as an agricultural resource and for its ecological complexity. Several species have been cultivated as food crops and cover crops: the common jack-bean (C. ensiformis) and sword bean (C. gladiata) are the best-known cultivated species, while C. ensiformis also serves as a living mulch suppressing weeds and soil pathogens. The common jack-bean is the commercial source of concanavalin A, a lectin widely used as a biochemical reagent in glycoprotein research and immunology, as well as purified urease enzyme used in scientific research.
The bay bean (C. rosea) has a long coastal pantropical distribution and is reportedly used in tobacco substitutes due to mild psychoactive properties when smoked. Among the more biogeographically distinctive members, the Hawaiian endemic species — called ʻāwikiwiki ("the very quick one") by Native Hawaiians — have suffered severe population declines following the introduction of herbivorous mammals to the islands, to which the plants had no prior evolutionary defenses.
Etymology
The genus name Canavalia is derived from kavavali, a Malabar (southwest Indian) word meaning "forest climber," the common name for Canavalia rosea in India. The name was formally adopted by Swiss botanist Augustin Pyramus de Candolle. The genus was still spelled Canavali as recently as 1913.
Distribution
Canavalia has a pantropical distribution, with species occurring across tropical Africa, Asia, Pacific islands, and the Americas. A distinct group of endemic species is found only in the Hawaiian Islands, where they occupy coastal and lowland habitats. The bay bean (C. rosea) is one of the most widely distributed species, occurring on tropical beaches and coastal strands throughout the pantropical zone.
Ecology
Some insects have evolved adaptations to overcome the defensive chemicals produced by jack-beans; caterpillars of the two-barred flasher butterfly (Astraptes fulgerator) are among the recorded feeders on Canavalia. The plant-pathogenic ascomycete fungus Mycosphaerella canavaliae was first described from a jack-bean host. Flowers are typically pollinated by solitary bees and carpenter bees such as Xylocopa confusa. Hawaiian endemic species appear to have lost chemical defenses over evolutionary time in the absence of herbivorous mammals, making them highly vulnerable once such mammals were introduced by humans.
Cultural Uses
Several Canavalia species have been cultivated as food crops in tropical regions for centuries. The common jack-bean (C. ensiformis) and sword bean (C. gladiata) are eaten as vegetables and fodder in parts of Africa, Asia, and Latin America. C. ensiformis is also used as a green manure and living mulch to suppress weeds and soil pathogens. The bay bean (C. rosea) has been used in some regions as a tobacco substitute. In addition, jack-beans are a commercial source of the lectin concanavalin A and urease enzyme used extensively in biochemical research.
