Plant 76

Vicia faba L. (Fabaceae)


Broad bean

Before Columbus's discovery of the Americas, beans, to the peoples of Europe, the Near East and North Africa, meant broad beans. Broad beans are legumes, grown in gardens or fields, to which the economies of multiple western civilisations pulsed. Garden beans and field (or horse) beans were thought to be different species by early academic botanists, although most gardeners were not fooled; the differences were due to the richer soils and extra care beans got in the garden.

The proverb, 'where beans thrive, fools grow', plays to classical notions that the heady scent of broad bean flowers induce nightmares and madness. Despite the olfactory dangers, broad beans have been grown across the warm, dry Mediterranean, and cooler, temperate regions of Europe and Asia, for thousands of years. Theophrastus, the Greek father of botany, discussed the biology and cultivation of broad beans in detail. Yet Pythagoras banned his disciples from eating beans and, at the end of his life, apparently refused to cross a field of flowering beans. This has led to speculation he suffered from favism, a hereditary condition that is brought on by exposure to specific alkaloids contained in broad beans.

The origin of broad beans remains a botanical enigma, despite the technological and intellectual advances made in understanding crops and their wild relatives. The overall appearance of the broad bean suggests its closest wild relatives are a group of Mediterranean and Near Eastern broad bean-like vetches. If this were the case, crossing these wild vetches with broad bean should produce hybrids; decades of research have failed to make such hybrids. Cytological investigations show that broad beans and these vetches have different chromosome numbers; 12 in broad bean and 14 in the vetches. Not only are broad beans reproductively and cytologically unique, detailed DNA analysis reveals they are genetically distinct from all other vetches. These data imply the wild relative may be rare, with a restricted distribution, which has not yet been discovered or the wild relative of the broad bean is extinct. Furthermore, broad beans have never been found outside of cultivation, suggesting they may have originated in cultivation.

Beans played three roles in pre-twentieth century western civilisations: as protein-rich food for humans and their livestock, and as a nitrogen-rich green manure. However, as industrially synthesised nitrogen fertilisers and other food and fodder stuffs have become commonplace, annual broad bean production has declined to about four million tonnes.

Further reading

Duc G et al. 2010. Diversity maintenance and use of Vicia faba L. genetic resources. Field Crops Research 115: 270-278.

Meletis J 2012. Favism: a brief history from the "abstain from beans" of Pythagoras to the present. Archives of Hellenic Medicine 29: 258-263.

Zohary D et al. 2013. Domestication of plants in the Old World. Oxford University Press.

Stephen Harris