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Family: Fabaceae

Kingdom: Plantae Rank: Family Parent: Fabales Status: Valid

Common Names:

  • LEGUME - English, United States of America
  • BEAN - English, United States of America
  • PULSE FAMILY - English, United States of America

Morphological Description

Family Recognition in the Field: Characteristic most helpful in field recognition is the legume fruit-a 1-chambered, pod-like, often bean-like fruit; other helpful clues include leaves with 3 leaflets and pea-like flowers, pinnately compound leaves with flowers in heads with obviously exserted stamens, or stamens in a 9 (fused) + 1 (separate) arrangement.

Diagnosis: Plants herbaceous or woody; leaves basal or alternate (sometimes crowded and appearing subopposite or whorled), compound or apparently simple (with only 1 leaflet); leaflets entire, or in a few genera toothed or lobed; stipules present (except Lotus and Crotalaria ), falling early in many species; flowers solitary or in racemes, panicles, spikes, heads, or umbel-like clusters; sepals 5, separate or united; petals 1-5, equal or in most genera unequal; stamens 5 to many; pistil 1; fruit a legume, developed from a 1-celled superior ovary with 1-many ovules and parietal placentation, in general opening along both sutures.


Notes: A huge (16,400 species in 657 genera), cosmopolitan, vegetatively variable family ranging from herbs to rain forest canopy trees; Ballenger et al. (1993) suggested there are ca. 20,000 species, while Cronquist (1993) indicated 18,000 species. Nearly a third of all species are in 6 large genera: Acacia, Astragalus, Cassia, Crotalaria , Indigofera, and Mimosa. The Fabaceae is the third largest angiosperm family in terms of numbers (after Asteraceae and Orchidaceae), and in importance to humans is second only to the Poaceae. It is also extremely important ecologically because of the symbiotic nitrogen-fixing Rhizobium bacteria associated with the roots of many species. The family includes many important timber trees, ornamentals, and particularly protein-rich food plants including Arachis (PEANUTS), Cicer (CHICK-PEAS), Glycine (SOYBEANS), Lens (LENTILS), Phaseolus (BEANS), and Pisum (PEAS); in fact, seeds of legumes are the world's most important source of vegetable protein for man and animals (Isely 1990). [a PLANT OF TOXIC/ POISONOUS NATURE]. There are often toxic, defensive, non-protein amino acids in the seeds or vegetative tissues as well as alkaloids. For example, the tropical Abrus precatorius L. (PRECATORY-BEAN or ROSARY-PEA) has striking red and black seeds sometimes used in necklaces; they contain abrin, a protein so toxic that a single chewed seed is enough to kill a human (Kingsbury 1964). The family, here recognized as having three subfamilies, is sometimes split into three questionably monophyletic families (e.g., Cronquist 1993). Recent evidence (Ballenger et al. 1993) suggested that the Caesalpinioideae is a basal paraphyletic assemblage from which the monophyletic Mimosoideae and Papilionoideae are derived. The tribal arrangement followed here is from Polhill and Raven (1981). The Fabaceae is the third largest family in the nc TX flora (after Asteraceae and Poaceae), with 176 species. Family name conserved from Faba, a genus of a single widely cultivated species, F. vulgaris Moench, BROAD BEAN, of the Mediterranean region; it is now usually lumped into Vicia as V. faba L. (Latin: faba, bean) (subclass Rosidae)