It includes trees, shrubs, and perennial or annual herbaceous plants, which are easily recognized by their fruit (legume) and their compound, stipulate leaves.

[13] This conclusion has been supported not only by the degree of interrelation shown by different groups within the family compared with that found among the Leguminosae and their closest relations, but also by all the recent phylogenetic studies based on DNA sequences.

[14][15][16] These studies confirm that the Fabaceae are a monophyletic group that is closely related to the families Polygalaceae, Surianaceae and Quillajaceae and that they belong to the order Fabales.

[18] The family Fabaceae includes a number of plants that are common in agriculture including Glycine max (soybean), Phaseolus (beans), Pisum sativum (pea), Cicer arietinum (chickpeas), Vicia faba (broad bean), Medicago sativa (alfalfa), Arachis hypogaea (peanut), Ceratonia siliqua (carob), Trigonella foenum-graecum (fenugreek), and Glycyrrhiza glabra (liquorice).

Fabaceae range in habit from giant trees (like Koompassia excelsa) to small annual herbs, with the majority being herbaceous perennials.

The Fabaceae have a wide variety of growth forms, including trees, shrubs, herbaceous plants, and even vines or lianas.

[3][9][18] Many species have leaves with structures that attract ants which protect the plant from herbivore insects (a form of mutualism).

Some species, like some in the genus Senna, have asymmetric flowers, with one of the lower petals larger than the opposing one, and the style bent to one side.

The two bottom petals are fused together at the apex (remaining free at the base), forming a boat-like structure called the keel.

[10] The Fabaceae diversified during the Paleogene to become a ubiquitous part of the modern earth's biota, along with many other families belonging to the flowering plants.

[23][24][25][26][27][28][29] The earliest fossils that can be definitively assigned to the Fabaceae appeared in the early Palaeocene (approximately 65 million years ago).

[22] In fact, a wide variety of taxa representing the main lineages in the Fabaceae have been found in the fossil record dating from the middle to the late Eocene, suggesting that the majority of the modern Fabaceae groups were already present and that a broad diversification occurred during this period.

[35][36][37][38] It has been suggested, based on fossil and phylogenetic evidence, that legumes originally evolved in arid and/or semi-arid regions along the Tethys seaway during the Palaeogene Period.

[44] The enzymes needed to reduce nitrogen, nitrogenases, require a substantial input of ATP but at the same time are sensitive to free oxygen.

To meet the requirements of this paradoxical situation, the plants express a type of haemoglobin called leghaemoglobin that is believed to be recruited after a duplication event.

[2] The family now includes six subfamilies:[4] The Fabaceae have an essentially worldwide distribution, being found everywhere except Antarctica and the high Arctic.

[3] Biological nitrogen fixation (BNF, performed by the organisms called diazotrophs) is a very old process that probably originated in the Archean eon when the primitive atmosphere lacked oxygen.

Some of these lineages co-evolved together with the flowering plants establishing the molecular basis of a mutually beneficial symbiotic relationship.

The spermatophytes that co-evolved with actinorhizal diazotrophs (Frankia) or with rhizobia to establish their symbiotic relationship belong to 11 families contained within the Rosidae clade (as established by the gene molecular phylogeny of rbcL, a gene coding for part of the RuBisCO enzyme in the chloroplast).

This grouping indicates that the predisposition for forming nodules probably only arose once in flowering plants and that it can be considered as an ancestral characteristic that has been conserved or lost in certain lineages.

The most distinctive characteristics that allow rhizobia to be distinguished apart are the rapidity of their growth and the type of root nodule that they form with their host.

The presence or absence of nodule-forming species within the three sub-families indicates that nodule formation has arisen several times during the evolution of the Fabaceae and that this ability has been lost in some lineages.

A second and closely related class of secondary metabolites that occur in many species of leguminous plants is defined by isoxazolin-5-one derivatives.

Other forage legumes such as Leucaena or Albizia are woody shrub or tree species that are either broken down by livestock or regularly cut by humans to provide fodder.

Grain legumes include both herbaceous plants like beans, lentils, lupins, peas and peanuts,[67] and trees such as carob, mesquite and tamarind.

Laburnum, Robinia, Gleditsia (honey locust), Acacia, Mimosa, and Delonix are ornamental trees and shrubs.

Industrial farmed legumes include Indigofera, cultivated for the production of indigo, Acacia, for gum arabic, and Derris, for the insecticide action of rotenone, a compound it produces.

Many Fabaceae species are important sources of pollen and nectar for bees, including for honey production in the beekeeping industry.

Yellow dyes are extracted from Butea monosperma, commonly called flame of the forest and from dyer's greenweed, (Genista tinctoria).

Their vast diversity of heights, shapes, foliage and flower colour means that this family is commonly used in the design and planting of everything from small gardens to large parks.