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The Fabaceae or Leguminosae, commonly known as the legume, pea, or bean family, are a large and economically important family of flowering plants. More...
The Fabaceae or Leguminosae, commonly known as the legume, pea, or bean family, are a large and economically important family of flowering plants.
The Fabaceae have an essentially worldwide distribution, being found everywhere except Antarctica and the high arctic.
The Fabaceae are placed in the order Fabales according to most taxonomic systems, including the APG III system. The family includes three subfamilies:
The fruit of Gymnocladus dioicus
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.
Main article: Root nodule
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 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 and are known as domatia.
A flower of Wisteria sinensis, Faboideae. Two petals have been removed to show stamens and pistil
The flowers often 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.