Legume Genomics and Genetics 2024, Vol.15, No.3, 93-104 http://cropscipublisher.com/index.php/lgg 94 2 Origins and Early Evolution of Legumes 2.1 Phylogeny and classification of the legume family (Fabaceae) The legume family, Fabaceae, is the third largest family of flowering plants, comprising approximately 800 genera and 20 000 species. Traditionally, Fabaceae has been divided into three subfamilies: Caesalpinioideae, Mimosoideae, and Papilionoideae, with the latter containing most of the major cultivated food and feed crops (Smýkal et al., 2015). Recent phylogenomic studies have provided a more robust framework for understanding the deep-branching relationships among these subfamilies, revealing that all six subfamilies of Fabaceae originated nearly simultaneously, challenging the traditional view of some subfamilies as ‘basal’ or ‘early-diverging’ (Figure 1) (Koenen et al., 2020). This simultaneous origin has significant implications for understanding the evolution of legume diversity and traits. Figure 1 Diversity, ecology and economic importance of legumes (Adopted from Koenen et al., 2019) Image caption: (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 (Adopted from Koenen et al., 2019)
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