The plants of this family almost exclusively tropical or sub-tropical in distribution. The family is represented by about 40 genera. Most members exhibit xeromorphic characteristics. The most common genera are; Acacia nilotica (kikar), mimosa pudica (lajvanti), Prosopis, Albizia lebbeck (shirin), etc.
Shrubs or tree, pinnate compound leaves, stipules are modified into thorns, inflorescence a spikate, head, flower hermaphrodite, actinomorphic, hypogynous, calyx 5 united, corolla 5 united, stamen numerous, ovary is with single carpal, fruit is a legume.
The representative species is Acacia nilotica (kikar or babul).
Acacia nilotica (kikar or babul):
A medium-sized evergreen spiny tree with dark-brown bark. The bark yields gum.
Erect, cylindrical, branched, woody.
Cauline and ramal, stipulate, stipules modified into spines, bipinnately compound, pulvinus present at the base of leaf, rachis possesses glands.
Opposite, sub-sessile, oval, reticulate unicostate, glabrous.
A compound cymose head.
Minute, ebracteate, sessile, complete, actinomorphic, bisexual, hypogynous, yellow in color.
5 sepals, membranous, gamosepalous, campanulate, slightly petaloid, inferior.
5 petals, gamopetalous, tubular, petals yellow in color, inferior.
Stamens indefinite, polyandrous, filament long, anthers minute, basfixed and yellow in color.
Monocaepellary, ovary superior and unilocular, placentation marginal, style long, stigma minute and capitate.
Floral Formula: K(5) C(5) A∞ G_1
Economic Importance of the Family:
The family is of great economic importance and ranks second, the first being Gramineae.
Source of Pulses:
The seeds of several plants yield all the various pulses like mong, mash, arhar, beans, grams and peas etc, which are commonly used as food stuffs, being rich in proteins and starches.
Source of Timber:
Many trees yield excellent timber e.g., Acacia, Dalbergia, Bauhinia, Gassia, tamarind and Prosopis.
Source of oil:
Some plants like Arrachis (ground-nut) yield oil and seeds which are edible. Ground-nut oil, when hydrogenated yields vegetable ghee.
Source of vegetables:
Several plants afford vegetables, e.g., Pisum (mattar), Vigna (Lobia), Glycine (soyabean), Trigonella (methe), Vicia (bakla), Dolichos (sem), Medicago (methi).
Most of them are used as chief fodder crops, e.g., Melilotus (senji), medicage (mena), Vicia (bakla) etc.
Source of Dyes:
Some yield valuable dyes, Indigofera (neel), Haematoxylon (haematoxylin) and Acacia: the bark of the latter yields tannin used in leather tanning.
Source of Gum Arabica:
Gum Arabica is obtained from the bark of Acacia Arabica and A. Senegal.
Katha is obtained from Acacia catechu.
Source of Fibers:
Grotolaria juncea-sunn-hemp and other species-yield fibers for rope making.
Many are cultivated as ornamental plants, in the gardens and planted along the road side, e.g., Lathyrus odoratus (Sweet Pea), Parkinsonia, Gaesalpinia, Poinciana, Bauhinias and Cassias. Some species of Glitoria and lupines are also grown in the gardens for their flowers.
Source of Lac:
The lac insect is often bred on Butea and Cajanus spp.
Source of Manure:
Many of the leguminous herbs and shrubs are used as green manure (clover).
Source of Fertility:
The presence of nitrifying in their root-nodules contributes to the fertility of the soil and this accounts for their frequent use in the rotation of the crops.
Source of Medicine:
Some plants yield medicine, e.g., Cassia fistula (amaltas), the pulp of which acts as a purgative.