Q.Describe the salient characteristics of family Fabaceae.
[!ANSWER] Family Fabaceae, placed under the subclass Polypetalae of Bentham and Hooker's classification, is characterised by its zygomorphic papilionaceous flower, a diadelphous (9+1) androecium, a monocarpellary superior ovary with marginal placentation, and a legume fruit, and it is one of the most economically valuable of all plant families.
Habit
Members of Fabaceae occur across a wide range of habits - herbs, shrubs, trees, and climbers - so habit alone cannot be used to recognise the family; the flower carries most of the diagnostic weight.
Root
The root system is typically a tap root, and a distinctive vegetative feature of the family is the frequent presence of root nodules, small swellings that house nitrogen-fixing bacteria in symbiosis with the plant - the basis of the family's value as green manure.
Stem
The stem may be erect, as in most cultivated pulses, or climbing/twining, as in many wild and ornamental members.
Leaf
Leaves are usually compound, most commonly pinnately compound or trifoliate, and typically bear a pair of stipules at the base of the leaf stalk.
Inflorescence
The inflorescence is usually a raceme, with flowers arranged along an elongated central axis.
Flower
The flower is bisexual and markedly zygomorphic (bilaterally symmetrical), distinguishing it immediately from the actinomorphic flowers of Solanaceae and Liliaceae.
Calyx
The calyx has five sepals fused together (gamosepalous) into a short tube with five lobes.
Corolla
The corolla is papilionaceous: five free petals of unequal size arranged as one large posterior standard (vexillum), two lateral wing petals (alae), and two anterior petals fused along their margins into a boat-shaped keel (carina) that encloses the reproductive whorls.
Androecium
There are typically ten stamens in the diadelphous condition - nine stamens fused by their filaments into a single sheath and the tenth free, described as the nine-plus-one arrangement - enclosing the ovary and style within the keel.
Gynoecium
The gynoecium is monocarpellary, formed from a single carpel, with a superior ovary and marginal placentation, the ovules attached along the fused margin of that one carpel.
Pollination
Pollination is mostly entomophilous: a visiting insect presses on the keel while probing for nectar, causing it to trip open and expose the previously hidden anthers and stigma, transferring pollen efficiently between flowers.
Fruit
The fruit is a legume (pod), a dry dehiscent fruit that splits along two sutures to release its seeds.
Economic Importance
Fabaceae is economically outstanding: as pulses (Pisum, Cicer) it is a major protein source; it yields edible oil, vegetables, and fodder for livestock; it supplies useful fibres and medicinal plants; it yields commercial gums and dyes; because of its nitrogen-fixing root nodules it is grown as green manure to enrich soil; and it supplies timber/wood as well as ornamentals grown for their attractive flowers. Pisum sativum, the garden pea, is the family's standard representative example, showing the typical zygomorphic papilionaceous flower and legume fruit described above.
[!ANSWER] Family Fabaceae is diagnosed by its zygomorphic, papilionaceous flower (standard, wings, keel), diadelphous 9+1 androecium, monocarpellary superior ovary with marginal placentation, and legume fruit, and it is economically vital as pulses, fodder, oil, fibre, medicine, green manure, timber, and ornamentals.
Unlock everything free for 14 days
- Full step-by-step solutions
- Concept-first explanations
- Methods, shortcuts & mistakes
- PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.