FABACEAE - the bean family

FABACEAE - the bean family

Systematic position

Class: Dicotyledonae

Sub-class: Polypetalae

Series: Calyciflorae

Order: Rosales

Family: Fabaceae

General characters

Distribution

Fabaceae includes about 482 genera and more than 7,200 species. The members are cosmopolitan in distribution but abundant in tropical and subtropical regions. In India, this family is represented by about 100 genera and 754 species.

Habit

The members of this family exhibit different habits. Prostrate herb eg. Indigofera enneaphylla (Seppu nerunji), erect herb (eg. Crotalaria verrucosa), twiner eg. Clitoria ternatea (Sangupoo), tendril climber eg. Pisum sativum (Pea plant), shrub eg. Cajanus cajan and trees eg. Pongamia glabra. Aeschynomene aspera (Pith plant) is a hydrophyte and commonly called pith plant.

Root

Branched tap root system having nodules. Nitrogen fixing bacterium Rhizobium leguminosarum occurs in the nodules.

Stem

Aerial, weak stem (eg. Clitoria ternatea) or woody (eg. Dalbergia latifolia).

Leaf

Simple (eg. Crotalaria juncea) or bifoliate (eg. Zornia diphylla) or trifoliate (eg. Lablab purpureus) or imparipinnately compound (eg. Clitoria ternatea), terminal leaflets modified into tendrils in Pisum sativum. Leaves are alternate, stipulate, leaflets stipellate, pulvinate showing reticulate venation.

Inflorescence

Usually a raceme eg. Crotalaria verrucosa (Kilukiluppai) or a panicle (eg. Dalbergia latifolia) or axillary solitary (eg. Clitoria ternatea).

Flower

Bracteate, pedicellate, bracteolate, complete, bisexual, pentamerous, dichlamydeous, zygomorphic and hypogynous.

Calyx

Sepals 5, green, gamosepalous showing valvate aestivation. Odd sepal is anterior in position.

Corolla

Petals 5, coloured, polypetalous showing descendingly imbricate or vexillary aestivation. The outer most petal is large called standard petal or vexillum. Two lateral petals are lanceolate and curved. They are called wing petals or alae. Two anterior and partly fused innermost petals are called keel petals or carina. The stamens and pistil are enclosed by these keel petals. All the petals have a claw at their bases. This type of irregular corolla is described as papilionaceous corolla.

Androecium

Stamens 10, usually diadelphous. Nine stamens are fused to form a bundle and the tenth stamen is free (9) + 1 (eg. Clitoria ternatea). The odd stamen is posterior in position. In Aeschynomene aspera, the stamens are fused to form two bundles each containing five stamens (5) + (5). In Crotalaria verrucosa the stamens are monadelphous and dimorphic i.e. 5 stamens have longer filaments and other 5 stamens have shorter filaments. Thus the stamens are found at two different levels and the shape of anthers also varies. 5 anthers are long and lanceolate. The other 5 anthers are short and blunt. Anthers are dithecous, basifixed and dehiscing longitudinally.

Gynoecium

Ovary superior, monocarpellary, stipitate i.e. ovary has a short stalk at the base. Ovary unilocular with one to many ovules showing marginal placentation. Style simple and bent. Stigma flattened or feathery.

Fruit

Typically a legume. In Arachis hypogea, the fruits develop underground. After fertilization, the stipe of the ovary becomes meristematic and grows down into the soil. Thus the ovary gets buried into the soil and develops into fruit.

Seed

Non-endospermous and kidney shaped.