Herbs, shrubs, trees, or vines/lianas, often with root nodules containing Rhizobium (nitrogen-fixing bacteria). Leaves usually alternate, simple or often compound with 1–many leaflets, pinnately (or bipinnately compound) to palmately compound, trifolioate or unifolioate, or rarely reduced to a phyllode-like rachis, entire to sometimes serrate, occasionally leaflets modified into tendrils, sometimes replaced by phyllodes or cladodes, rarely absent; pulvinus of leaf and individual leaflets well developed; stipules present, paired. Inflorescence various; flowers in terminal panicles or pseudoracemes, or axillary racemes, spikes or clusters, sometimes cauliflorous; each flower on a short or long pedicel or sessile, subtended by a bract and a pair of similar bracteoles attached on, or just below, the calyx. Flowers irregular or regular, usually bisexual. Sepals 5, free or fused, often 2-lipped. Petals usually 5, free or variously united, all alike, or the upper petal (standard) differentiate in colour, size of shape, usually the largest and more or less erect, lateral petals (wings) 2, lower petals (keel) 2, usually fused and enclosed by the wings and enclosing the stamens and style. Stamens 5, 10 or many, but usually 10, free or variously joined by their filaments, dehiscing by longitudinal slits. Carpel 1 (rarely 2–16), free; ovary superior, 1-celled or rarely partly 2-celled, placentation lateral; style single, slender, tapering, stigma small, usually terminal; ovules 1-many per carpel. Fruit usually an oblong pod (legume), sometimes a samara, loment, follicle, indehiscent pod, achene, drupe, or berry. Seeds 1-many, usually arillate, sometimes with a U-shaped line (pleurogram).
The subfamily classification outlined here follows the most recent phylogenetic analyses published by The Legume Phylogeny Working Group (LPWG 2017) that recognises a single family with six subfamilies. These subfamilies are known collectively as legumes because most have a pod as fruit. Some of the subfamilies such as Caesalpiniaceae, Fabaceae and Mimosaceae were commonly treated as separate families prior to the molecular analyses. The descriptions of the subfamilies provided here is a summarised version taken from LPWG (2017).
A cosmopolitan family of about 770 genera and over 19,500 species (LPWG 2013; LPWG 2017); about 200 genera in Australia.
Subfamily Caesalpinioideae: Trees or shrubs, rarely herbs or vines. Leaves pinnate or bipinnate, rarely of one leaflet or simple or reduced to phyllodes; usually pulvinate. Specialised extrafloral nectaries often present on the petiole and / or on the primary and secondary rachises, usually between pinnae or leaflet pairs, rarely stipular or bracteal. Stipules absent or small mostly small and caducous, but sometimes of stout spines. Inflorescences of heads, racemes, spikes or cymes, sometimes cauliflorous. Flowers regular or irregular, generally bisexual, sometimes unisexual (e.g. Ceratonia, Gleditsia, and plants monoecious or dioecious) or neuter; bracteoles small or absent; sepals (3–)5(–6), free or fused; petals (3–)5(–6), free or fused (the sepal or petal or both whorls sometimes lacking), the upper petal sometimes overlapped by the lateral ones; stamens 3, 5 or 10 or numerous (100 +), free or united below, sometimes of two unequal sets or some staminodal, and protruding from the flower; anthers usually dehiscing by longitudinal slits, but sometimes with apical or basal pores, often with a stipitate or stalkless apical gland. Gynoecium 1(–many) carpellate, 1–many-ovulate. Fruit a 1–many-seeded pod, dehiscent along one or both sutures, also pod often constricted between the seeds (lomentum), or pod splitting into 1-seeded segments (craspedium), or thick and woody and then indehiscent or explosively dehiscent, often curved or spirally coiled. Seeds usually with pleurograms.
Mainly a warm-climate subfamily that is well-represented in horticulture, Acacia, Caesalpinia, Cassia, Gleditsia, Parasarianthes, and Senna being popular genera. A number of species are grown widely in the tropics, including Adenanthera pavonina L., Red Sandalwood, from SE Asia, grown in warm regions, often as a street tree; Delonix regia (Bojer ex Hook.) Raf., Royal Poincinia, from Madagascar is occasionally grown in warmer districts; it has bipinnate leaves, scarlet and yellow petals, scarlet filaments and pods more than 20 cm long; it has become naturalised at Christmas Is., WA, NT, Qld, and NSW; Inga edulis Mart., from C and S America, which has pods with an edible sweet pulp; Prosopis species introduced for ornament, erosion control and stabilisation and naturalised in WA, NT, SA, Qld, NSW and Vic; and Samanea saman (Jacq.) Merr. from South America, grown throughout the tropics as a shade tree.
Timber is harvested from species of Caesalpinia, Afzelia and other genera, dyes from Haematoxylum, medicines from Senna, and edible fruits from Schotia. See also under individual genera.
Many plants formerly placed in Cassia are now placed in the genus Senna.
About 148 genera with perhaps 4400 species worldwide, predominantly in tropical and subtropical regions, particularly South America, tropical Africa and SE Asia; 22 genera and about 130 species in Australia.
The revised concept Caesalpinioideae now includes the families Caesalpiniaceae and Mimosaceae, which were previously treated either as separate from Fabaceae, or as two separate subfamilies of Fabaceae.
Subfamily Cercidoideae: Trees or shrubs, sometimes semi-scandent, or lianas, unarmed or armed with intrapetiolar spines. Branches rarely modified into cladodes. Specialised extrafloral nectaries sometimes present (Bauhinia), stipular, never on petiole and leaf rachis. Leaves simple, bilobed or with 2 separate leaflets. Stipules present, deciduous or persistent. Bracteoles minute to large, deciduous or persistent. Flowers bisexual, rarely unisexual (plants polygamous or dioecious), slightly to strongly bilaterally symmetrical, sometimes papilionate (Cercis). Sepals fused above hypanthium; tube shortly to deeply lobed or spathe-like or 5-partite. Petals free, 5, rarely 2, 6 (some Bauhinia) or absent, the adaxial petal innermost and frequently differentiated; stamens usually 10 or fewer) in two whorls of alternate length, the filaments partly united or free, anthers dehiscing by a longitudinal slit or rarely by pores. Seeds lacking pleurograms.
Bauhinia is widely cultivated in warm-climate regions. Cercis (Redbuds) are widely cultivated as ornamental trees in the United States and Europe.
12 genera, c. 335 species, pantropical; 2 genera in Australia, 8 species.
Subfamily Detarioideae: Trees, sometimes shrubs. Specialised extrafloral nectaries often present abaxially, rarely on the margins of leaflets or on leaf rachis, and never on the petiole. Leaves simply pinnate, rarely unifoliate or simple. Stipules intrapetiolar, if vestigial then bud scales usually well-developed. Bracteoles usually present, small or large, commonly petaloid. Inflorescence a raceme or panicle. Flowers bisexual or with both bisexual and male flowers radially or slightly to strongly bilaterally symmetrical (but never papilionate) Sepals 4–6, free to base, or two adaxial sepals often fused. Petals petals free, 0–5(–7), all equal or the adaxial large and either the other 4 or only the abaxial ones smaller to rudimentary. Stamens usually 2-numerous but usually 10, the filaments partly united or free, staminodes occasionally present; anthers dehiscing by longitudinal slits. Carpel 1, ovules 1-many. Fruits mostly woody, dehiscent pods, sometimes indehiscent and woody or thin-valved, samaroid, or rarely filled with a pulpy inner layer. Seeds occasionally with pleurograms.
Tamarindus indica L. (Tamarind) is the most well known member of the subfamily, and is widely cultivated in tropical areas for its edible fruit. Timber is harvested from Cynometra alexandri C.H.Wright (Uganda Ironwood or Muhimbi) in central and east Africa, and Sindora supa Merr. is an important timber tree in the Philippines, oil from the timber is used in marine paint and varnish.
About 84 genera and c. 760 species, tropical and subtropical; 6 genera and 6 species in Australia.
Subfamily Faboideae (Papilionoideae): Trees, shrubs, herbs or vines. Specialised extrafloral nectaries absent on petiole and leaf rachis, occasionally stipular, stipellar or bracteal nectaries, or swollen and nectar-secreting peduncles, rarely on sepals (Erythrina). Stipules almost always in lateral position, free or absent. Leaves mostly pari or imparipinnate to palmately compound, also often uni- or trifoliolate, rarely bi- or tetrafoliolate, never bipinnate. Inflorescence often racemose, paniculate, cymose or spicate, axillary or terminal, or flowers solitary. Bracteoles usually present. Flowers bisexual, rarely unisexual, usually zygomorphic. Sepals (3–)5, united at least at base. Corolla usually papilionate, petals unequal, adaxial petal (the standard) usually largest and borne outside the 2 adjacent lateral petals (wings), the 2 abaxial petals (the keel) are innermost, usually fused and enfolding the stamens and gynoecium. Stamens usually 10, rarely 9 or many, free or variously joined by their filaments, forming a closed or open sheath around the gynoecium, anthers dehiscing by longitudinal slits. Gynoecium 1-carpellate, very rarely 2-carpellate, 1–many-ovuled. Fruit a pod dehiscing along one or both sutures or indehiscent, or a loment, samara or drupe. Seeds lacking pleurograms.
About 500 genera with c. 14 000 species cosmopolitan, the woody and/or climbing species mostly from the tropics, herbaceous species from temperate regions.; about 150 to 160 genera and about 1700 to 2000 species in Australia.
Rarely cultivated plants include the following: Baphia racemosa (Hochst.) Walp., Camwood, from S Africa, a shrub with clusters of purple-veined white flowers; Bolusanthus speciosus (Bolus) Harms, Rhodesian Wisteria, a small tree with Wisteria-like clusters of violet flowers; Calpurnia aurea (Ait.) Benth., East African Laburnum, a shrub or small tree with Laburnum-like clusters of yellow flowers; Caragana arborescens Lam., Siberian Pea Tree, with showy yellow flowers and grown as the cultivar 'Walker'; Clitoria ternatea L., a remarkable twiner of warmer climates with dark blue flowers having lighter markings (sometimes double-flowered or white) and naturalised in WA, NT and Qld; Erinacea anthyllis Link, a Mediterranean blue or violet-flowered compact, thorny shrub to about 30 cm tall; Gompholobium confertum (DC.) Crisp and G. scabrum Sm., heath-like native shrubs from WA with purplish flowers at the branch tips; Lessertia frutescens (L.) Goldblatt and J.C.Manning, Cancer Bush, a S African shrub to about 1 m tall, with red flowers 2.5-4 cm long and an inflated pod that has become naturalised in WA, SA, NSW and Vic; and Tipuana tipu (Benth.) O. Kuntze, Tipu Tree (Rosewood), from S America, which looks like a Sophora but has a remarkable winged fruit like the samara of maples - there are excellent mature specimens at the Melbourne Royal Bot. Gds (Bell Shed group) and Dookie Agricultural College (now part of Melbourne University), Vic.
Many legumes are grown for the edible pods and seeds or as fodder and green manure. Among those more widely available are the following. Alysicarpus bupleurifolius (L.) DC.., Alyce Clover, is a good fodder as nutritious as alfalfa. Cajanus cajan (L.) Millsp., Pigeon Pea (Congo Pea), possibly native to India, has large edible seeds known as dhal (a name often used in India to refer to all legumes): it is also cultivated as a green manure but has become naturalised from near Coffs Harbour northwards. Australia has 10 native species. Canavalia, Jack Bean, is grown in warmer tropical regions as the ornamentals, C. ensiformis (L.) DC. from tropical America (young seed poisonous) and C. gladiata (Jacq.) DC., Sword Bean, from the Old World tropics. Both are used as stock feed or green manure, and the mature beans are edible. Centrosema molle Mart. ex Benth., Butterfly Pea, is a green feed of warmer regions. Cicer arietinum L., Chick Pea, is eaten fresh or dry and is second only to peas and beans in popularity; it is also made into flour and used as a coffee substitute; Cyamopsis tetragonolobus (L.) Taub., Cluster Bean, from warm-climate regions of the world has young pods used for forage and a seed gum used in shampoo. Hedysarum coronarium L., French Honeysuckle, is a biennial or perennial from Europe growing to over 1 m tall; it has pinnate leaves of 7-15 leaflets and fragrant, deep red flowers about 2 cm long. Lablab purpureus (L.) Sweet, Lablab (Hyacinth Bean, Bonavist), is a woody Old World perennial climber with rhombic to triangular leaves and purple or white flowers; it is grown widely in the tropics as an annual. Syn. Dolichos lablab L. Medicago sativa L., Alfalfa (Lucerne) is, with several other species in this genus, widely used as fodder and green manure with 14 PBR applications granted to 1999. Onobrychis viciifolia Scop., Sainfoin or Holy Clover, from Asia is used for fodder and to attract bees. Ornithopus sativus Brot., Serradella, from the Mediterranean is used as fodder. Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen & S.M.Almeida ex Sanjappa & Predeep, Kudzu, native to China and Japan is sometimes used as a green manure or fodder plant and has become naturalised in Qld and NSW; it has 3 leaflets, each of which is irregularly lobed.
An extremely important family commercially, with many food and fodder plants (see above for green manure and fodder plants grown in Australia). In many species nitrogen-fixing bacteria form root nodules; these species are grown as green manure in crop rotation programs to improve soil fertility and as a source of fodder. The most widely used genera are Lupinus (Lupin), Trifolium (Clover) and Medicago (Lucerne). Important human food plants include Arachis hypogaea (Peanut), Cicer arietinum (Chick Pea), Glycine max (Soybean), Lens culinaris (Lentil), Phaseolus aureus (Mung Bean), Phaseolus coccineus (Runner Bean), Phaseolus lunatus (Lima Bean), Phaseolus vulgaris (French, Green or Haricot Bean, etc.), Pisum sativum (Pea) and Vicia faba (Broad Bean).
Polhill & Raven (1981). Economics: Duke (1981); The Legume Phylogeny Working Group (LPWG 2017).
Source: (2002). Fabaceae. In: . Horticultural Flora of South-eastern Australia. Volume 3. Flowering plants. Dicotyledons. Part 2. The identification of garden and cultivated plants. University of New South Wales Press.
Updated by: Val Stajsic, June 2018