Fabaceae or Leguminosae is a large and economically important family of flowering plants, which is commonly known as the legume family, pea family, bean family or pulse family. The name 'Fabaceae' comes from the defunct genus Faba, now included into Vicia. Leguminosae is an older name still considered valid, and refers to the typical fruit of these plants, which are called legumes.
Fabaceae is the third largest family of flowering plants, behind Orchidaceae and Asteraceae, with 730 genera and over 19,400 species, according to the Royal Botanical Gardens. The largest genera are Astragalus with more than 2,000 species, Acacia with more than 900 species, and Indigofera with around 700 species. Other large genera include Crotalaria with 600 species and Mimosa with 500 species.
The species of this family are found throughout the world, growing in many different environments and climates. A number are important agricultural plants, including: Glycine max (soybean), Phaseolus (beans), Pisum sativum (pea), Cicer arietinum (chickpeas), Medicago sativa (alfalfa), and Arachis hypogaea (peanut), which are among the best known members of Fabaceae. A number of species are also weedy pests in different parts of the world, including: Cytisus scoparius (broom) and Pueraria lobata (kudzu), and a number of Lupinus species.
The Fabaceae comprise three subfamilies (with distribution and some representative species):
- Mimosoideae: 80 genera and 3,200 species. Mostly tropical and warm temperate Asia and America. Mimosa, Acacia.
- Caesalpinioideae: 170 genera and 2,000 species, cosmopolitan. Senna, Bauhinia, Amherstia.
- Faboideae: 470 genera and 14,000 species, cosmopolitan. Astragalus, Lupinus.
These three subfamilies have been alternatively treated at family level, as in the Cronquist and Dahlgren systems. However, this choice has not been supported by late 20th and early 21st century evidence, which has shown the Caesalpinioideae to be paraphyletic and the Fabaceae sensu lato to be monophyletic.
The subfamilial name Papilionoideae for Faboideae is approved by the International Code of Botanical Nomenclature, as is 'Leguminosae' for the Fabaceae s.l..
While the Mimosoideae and the Faboideae are largely monophyletic, the Caesalpinioideae appear to be paraphyletic and the tribe Cercideae is probably sister to the rest of the family. Moreover, there are a number of genera whose placement into the Caesalpinioideae is not always agreed on (e.g. Dimorphandra).
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.
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), thorn-like (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 that 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.
The flowers always have five generally fused sepals and five free petals. They are generally hermaphrodite, 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 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 ten, have long coloured filaments, which are the most showy part of the flower. All of the flowers in an inflorescence open at once.
In the Faboideae, the flowers are always zygomorphic, and have a specialized structure. The upper petal, called the banner, 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.
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.
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.
The history of legumes is tied in closely with that of human civilization, appearing early in Asia, the Americas (the common bean, several varieties) and Europe (broad beans) by 6,000 BC, where they became a staple, essential for supplementing protein where there was not enough meat.
Their ability to fix atmospheric nitrogen reduces fertilizer costs for farmers and gardeners who grow legumes, and means that legumes can be used in a crop rotation to replenish soil that has been depleted of nitrogen. Legume seeds and foliage have a comparatively higher protein content than non-legume materials, due to the additional nitrogen that legumes receive through the process.
Farmed legumes can belong to numerous classes, including forage, grain, blooms, pharmaceutical/industrial, fallow/green manure and timber species, with most commercially farmed species filling two or more roles simultaneously.
There are of two broad types of forage legumes. Some, like alfalfa, clover, vetch, and Arachis, are sown in pasture and grazed by livestock. 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 stock feed.
Grain legumes are cultivated for their seeds, and are also called pulses. The seeds are used for human and animal consumption or for the production of oils for industrial uses. Grain legumes include both herbaceous plants like beans, lentils, lupins, peas and peanuts. and trees such as carob, mesquite and tamarind.
Bloom legume species include species such as lupin, which are farmed commercially for their blooms as well as being popular in gardens worldwide. Laburnum, Robinia, Gleditsia, Acacia, Mimosa, and Delonix are ornamental trees and shrubs.
Fallow or green manure legume species are cultivated to be tilled back into the soil to exploit the high nitrogen levels found in most legumes. Numerous legumes are farmed for this purpose, including Leucaena, Cyamopsis and Sesbania.
Acacia baileyana (Wattle)
Loment of Alysicarpus vaginalis
Dichrostachys cinerea Sickle Bush
Tendrils of Lathyrus odoratus (Sweet pea)
Inflorescence of Lupinus arboreus (Yellow bush lupin)
Pisum sativum (Peas); note the leaf-like stipules
- ^ a b c Wojciechowski, M. F.; Lavin, M.; Sanderson, M. J. (2004). "A phylogeny of legumes (Leguminosae) based on analysis of the plastid matK gene resolves many well-supported subclades within the family". American Journal of Botany 91: 1846. doi:10.3732/ajb.91.11.1846.
- ^ International Code of Botanical Nomenclature Art. 18.5 (Vienna Code)
- ^ a b c Martin F. Wojciechowski, Johanna Mahn, and Bruce Jones (2006). "Fabaceae". The Tree of Life Web Project. http://tolweb.org/Fabaceae/21093/2006.06.14.
- ^ The gene bank and breeding of grain legumes (lupine, vetch, soya and beah) / B.S. Kurlovich and S.I. Repyev (Eds.), - St. Petersburg, The N.I. Vavilov Institute of Plant Industry, 1995, 438p. - (Theoretical basis of plant breeding. V.111)