Figure 1.

Diversity, ecology and economic importance of legumes. (a–f) The family is subdivided into six subfamilies: (a) Cercidoideae (Bauhinia madagascariensis); (b) Detarioideae (Macrolobium angustifolium); (c) Duparquetioideae (Duparquetia orchidacea); (d) Dialioideae (Baudouinia sp.); (e) Caesalpinioideae (Mimosa pectinatipinna); and (f) Papilionoideae (Medicago marina). (g) While the family has a very diverse floral morphology, the fruit (Brodriguesia santosii), which comes in many shapes and is most often referred to as a 'pod' or 'legume', is the defining feature of the family. (h) A large fraction of legume species is known to fix atmospheric nitrogen symbiotically with 'rhizobia', bacteria that are incorporated in root nodules, for example in Lupinus nubigenus. (i) Economically, the family is the second most important of flowering plants after the grasses, with a wide array of uses, including timber, ornamentals, fodder crops, and, notably, pulse crops such as peanuts (Arachis hypogaea), beans (Phaseolus vulgaris), chickpeas (Cicer arietinum) and lentils (Lens culinaris). (j–l) Ecologically, legumes are also extremely diverse and important, occurring and often dominating globally across disparate ecosystems, including: wet tropical forest, for example, Albizia grandibracteata in the East African Albertine Rift (j); savannas, seasonally dry tropical forests, and semi‐arid thorn‐scrub, for example. Mimosa delicatula in Madagascar (k); and temperate woodlands and grasslands, for example, Vicia sylvatica in the European Alps (l). Photographs: (a, b, d, i–l) Erik Koenen; (c) Jan Wieringa; (e–h) Colin Hughes.