Fabaceae or Leguminosae, commonly known as the legume, pea, or bean family, is a large and agriculturally important family of flowering plants. It includes trees, shrubs, and perennial or annual herbaceous plants, which are easily recognized by their fruit (legume) and their compound, stipulate leaves. The family is widely distributed, and is the third-largest land plant family in number of species, behind only the Orchidaceae and Asteraceae, with about 765 genera and nearly 20,000 known species.Judd, W.S.; Campbell, C.S.; Kellogg, E.A.; Stevens, P.F.; & Donoghue, M.J. (2002). Plant systematics: a phylogenetic approach, Sinauer Axxoc, 287–292. .
The five largest genera of the family are Astragalus (over 3,000 species), Acacia (over 1,000 species), Indigofera (around 700 species), Crotalaria (around 700 species), and Mimosa (around 400 species), which constitute about a quarter of all legume species. The known legume species amount to about 7% of flowering plant species. Fabaceae is the most common family found in tropical rainforests and dry forests of the Americas and Africa.
Recent molecular and morphological evidence supports the conclusion that the Fabaceae is a single monophyletic family.Lewis, G.; Schrire, B.; Mackinder, B.; & Lock, M. (eds.) Legumes of the world. Royal Botanic Gardens, Kew, UK. 577 pages. 2005. . 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.Doyle, J.J.; Chappill, J.A.; Bailey, C.D.; & Kajita, T. 2000. "Towards a comprehensive phylogeny of legumes: evidence from rbcL sequences and non-molecular data", pp. 1–20 in Advances in legume systematics, part 9, (P. S. Herendeen and A. Bruneau, eds.). Royal Botanic Gardens, Kew, UK. 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.
Along with the cereals, some fruits and tropical roots, a number of Leguminosae have been staple human foods for millennia, and their use is closely related to human evolution.Burkart, A. Leguminosas. In: Dimitri, M. 1987. Enciclopedia Argentina de Agricultura y Jardinería. Tomo I. Descripción de plantas cultivadas. Editorial ACME S.A.C.I., Buenos Aires. pages: 467–538.
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), Vigna unguiculata (cowpea), Medicago sativa (alfalfa), Arachis hypogaea (peanut), Ceratonia siliqua (carob), Tamarindus indica (tamarind), Trigonella foenum-graecum (fenugreek), and Glycyrrhiza glabra (liquorice). A number of species are also weedy pests in different parts of the world, including Cytisus scoparius (broom), Robinia pseudoacacia (black locust), Ulex europaeus (gorse), Pueraria montana (kudzu), and a number of Lupinus species.
Etymology The name 'Fabaceae' comes from the defunct genus Faba, now included in Vicia. The term "faba" comes from Latin, and means "bean". Leguminosae is an older name still considered valid,International Code of Nomenclature for algae, fungi, and plants. Article 18.5 states: "The following names, of long usage, are treated as validly published: ....Leguminosae (nom. alt.: Fabaceae; type: Faba Mill. [= Vicia L.]); ... When the Papilionaceae are regarded as a family distinct from the remainder of the Leguminosae, the name Papilionaceae is conserved against Leguminosae." English pronunciations are as follows: , and . and refers to the fruit of these plants, which are called legumes.
Description
Fabaceae range in habit from giant trees (like Koompassia excelsa) to small annual herbs, with the majority being herbaceous perennials. Plants have indeterminate inflorescences, which are sometimes reduced to a single flower. The flowers have a short hypanthium and a single carpel with a short gynophore, and after fertilization produce fruits that are legumes.
Growth habit The Fabaceae have a wide variety of growth forms, including trees, shrubs, herbaceous plants, and even vines or lianas. The herbaceous plants can be annuals, biennials, or perennials, without basal or terminal leaf aggregations. Many Legumes have tendrils. They are upright plants, epiphytes, or vines. The latter support themselves by means of shoots that twist around a support or through cauline or foliar tendrils. Plants can be heliophytes, mesophytes, or xerophytes.
Leaves The leaves are usually alternate and compound. Most often they are even- or odd-pinnately compound (e.g. Caragana and Robinia respectively), often trifoliate (e.g. Trifolium, Medicago) and rarely palmately compound (e.g. Lupinus), in the Mimosoideae and the Caesalpinioideae commonly bipinnate (e.g. Acacia, Mimosa). They always have stipules, which can be leaf-like (e.g. Pisum), thornlike (e.g. Robinia) or be rather inconspicuous. Leaf margins are entire or, occasionally, serrate. Both the leaves and the leaflets often have wrinkled pulvini to permit nastic movements. In some species, leaflets have evolved into tendrils (e.g. Vicia).
Many species have leaves with structures that attract ants which protect the plant from herbivore insects (a form of mutualism). Extrafloral nectaries are common among the Mimosoideae and the Caesalpinioideae, and are also found in some Faboideae (e.g. Vicia sativa). In some Acacia, the modified hollow stipules are inhabited by ants and are known as domatia.
Roots
Many Fabaceae host bacteria in their roots within structures called root nodules. These bacteria, known as rhizobia, have the ability to take nitrogen gas (N2) out of the air and convert it to a form of nitrogen that is usable to the host plant (NO3− or NH3). This process is called nitrogen fixation. The legume, acting as a host, and rhizobia, acting as a provider of usable nitrate, form a symbiotic relationship. Members of the Phaseoleae genus Apios form tubers, which can be edible.
Flowers
The flowers often have five generally fused sepals and five free petals. They are generally hermaphroditic and have a short hypanthium, usually cup-shaped. There are normally ten stamens and one elongated superior ovary, with a curved style. They are usually arranged in indeterminate inflorescences. Fabaceae are typically entomophilous plants (i.e. they are pollinated by insects), and the flowers are usually showy to attract pollinators.
In the Caesalpinioideae, the flowers are often zygomorphic, as in Cercis, or nearly symmetrical with five equal petals, as in Bauhinia. The upper petal is the innermost one, unlike in the Faboideae. 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 calyx, corolla, or stamens can be showy in this group.
In the Mimosoideae, the flowers are actinomorphic and arranged in globose inflorescences. The petals are small and the stamens, which can be more than just 10, have long, coloured filaments, which are the showiest part of the flower. All of the flowers in an inflorescence open at once.
In the Faboideae, the flowers are zygomorphic, and have a specialized structure. The upper petal, called the banner or standard, is large and envelops the rest of the petals in bud, often reflexing when the flower blooms. The two adjacent petals, the wings, surround the two bottom petals. The two bottom petals are fused together at the apex (remaining free at the base), forming a boat-like structure called the keel. The stamens are always ten in number, and their filaments can be fused in various configurations, often in a group of nine stamens plus one separate stamen. Various genes in the CYCLOIDEA (CYC)/DICHOTOMA (DICH) family are expressed in the upper (also called dorsal or adaxial) petal; in some species, such as Cadia, these genes are expressed throughout the flower, producing a radially symmetrical flower.
Fruit The ovary most typically develops into a legume. A legume is a simple dry fruit that usually dehisces (opens along a seam) on two sides. A common name for this type of fruit is a "pod", although that can also be applied to a few other fruit types. A few species have evolved samarae, loments, follicles, indehiscent legumes, achenes, drupes, and berries from the basic legume fruit.
Physiology and biochemistry The Fabaceae are rarely cyanogenic. Where they are, the cyanogenic compounds are derived from tyrosine, phenylalanine or leucine. They frequently contain alkaloids. Proanthocyanidins can be present either as cyanidin or delphinidine or both at the same time. Flavonoids such as kaempferol, quercitin and myricetin are often present. Ellagic acid has never been found in any of the genera or species analysed. Sugars are transported within the plants in the form of sucrose. C3 photosynthesis has been found in a wide variety of genera. The family has also evolved a unique chemistry. Many legumes contain toxic and indigestible substances, antinutrients, which may be removed through various processing methods. Pterocarpans are a class of molecules (derivatives of isoflavonoids) found only in the Fabaceae. Forisome proteins are found in the sieve tubes of Fabaceae; uniquely they are not dependent on ATP.
Evolution, phylogeny and taxonomy
Evolution The order Fabales contains around 7.3% of eudicot species and the greatest part of this diversity is contained in just one of the four families that the order contains: Fabaceae. This clade also includes the families Polygalaceae, Surianaceae and Quillajaceae and its origins date back 94 to 89 million years, although it started its diversification 79 to 74 million years ago. 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.Herendeen, P. S., W. L. Crepet, and D. L. Dilcher. 1992. The fossil history of the Leguminosae: phylogenetic and biogeographic implications. Pages 303 – 316 in Advances in Legume Systematics, part 4, the fossil record (P. S. Herendeen and D .L. Dilcher, eds). Royal Botanic Gardens, Kew, UK.