Fabaceae, also known as Leguminosae, is commonly called the legume, pea, or bean family. It is the third-largest family of flowering plants on land, encompassing approximately 765 genera and nearly 20,000 known species — roughly 7% of all flowering plant species. The family sits within the order Fabales and is closely related to the families Polygalaceae, Surianaceae, and Quillajaceae.
Members range enormously in habit, from towering tropical trees such as Koompassia excelsa to small annual herbs. The family is most easily recognised by two features: its distinctive fruit, the legume (a pod that typically splits along two seams), and its compound, stipulate leaves. Flowers have a short hypanthium and a single carpel.
The family is divided into six subfamilies. Faboideae (Papilionoideae) is the largest, with 503 genera and around 14,000 species and a cosmopolitan range. Caesalpinioideae (which now absorbs the former Mimosoideae) comprises 148 genera and roughly 4,400 species and is pantropical. The remaining four subfamilies — Cercidoideae, Detarioideae, Duparquetioideae, and Dialioideae — are smaller and predominantly tropical.
The five largest genera are Astragalus (over 3,000 species), Acacia (over 1,000 species), Indigofera and Crotalaria (each around 700 species), and Mimosa (around 400 species), together accounting for roughly a quarter of all legume species. Fabaceae is the most common plant family in tropical rainforests and dry forests of the Americas and Africa.
Economically, the family is among the most important in agriculture. It includes soybean (Glycine max), common beans (Phaseolus), pea (Pisum sativum), chickpea (Cicer arietinum), broad bean (Vicia faba), alfalfa (Medicago sativa), peanut (Arachis hypogaea), carob (Ceratonia siliqua), tamarind (Tamarindus indica), fenugreek (Trigonella foenum-graecum), and liquorice (Glycyrrhiza glabra). Along with cereals, legumes have been staple foods for millennia and played a significant role in human evolution.
Etymology
The name Fabaceae is derived from Faba, a now-defunct genus whose species are today included in Vicia; the Latin word faba means "bean". The alternative family name Leguminosae is older and remains nomenclaturally valid; it refers to the characteristic fruit of the family, the legume.
Distribution
Fabaceae has an essentially worldwide distribution, absent only from Antarctica and the high Arctic. Trees dominate in tropical regions, while herbaceous plants and shrubs are most prevalent in temperate zones. The family is the most common in tropical rainforests and dry forests of the Americas and Africa.
Ecology
Many legume genera — including Astragalus, Coronilla, Indigofera, and Lotus — produce 3-nitropropanoic acid (3-NPA), an irreversible inhibitor of mitochondrial respiration that is particularly toxic to nerve cells and is thought to play a significant defensive ecological role. A related class of secondary metabolites, isoxazolin-5-one derivatives, co-occurs with 3-NPA in species such as Astragalus canadensis.
History
Legumes have been cultivated as staple foods alongside cereals for thousands of years, and their domestication is considered closely tied to the development of human civilisation. The family's agricultural importance spans crops used for human food, animal fodder, soil enrichment (via nitrogen fixation), and industrial products.
Taxonomy Notes
Fabaceae is placed in the order Fabales under the APG III system and is confirmed as monophyletic by molecular and morphological evidence. The family's closest relatives are Polygalaceae, Surianaceae, and Quillajaceae. It comprises six subfamilies: Cercidoideae, Detarioideae, Duparquetioideae, Dialioideae, Caesalpinioideae (which now includes the former Mimosoideae), and Faboideae (Papilionoideae).
