Groundnut, horse-gram, and soybean look nothing alike on a plate. Botanically, all three belong to exactly the same plant family.
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All Three Belong to the Pea Family
Groundnut, horse-gram, and soybean — all genuine Fabaceae members
GroundnutArachis hypogaea
Horse-gramMacrotyloma uniflorum
SoybeanGlycine max
What unites them: about 90% of Fabaceae species fix atmospheric nitrogen, through root nodules housing symbiotic rhizobia bacteria — a key reason legumes are used in crop rotation.
🏛️ Must Know
The Pea Family, Fabaceae
- Two Names Fabaceae is the currently preferred botanical name for the pea family. Leguminosae is an older name for the same family, still widely accepted.
- Three Genuine Members Groundnut (Arachis hypogaea), horse-gram (Macrotyloma uniflorum), and soybean (Glycine max) all genuinely belong to Fabaceae, despite looking very different as food crops.
- Seed Pods Fabaceae members produce their seeds in pods, one of the family’s defining structural traits.
🏘️ Good to Know
Nitrogen Fixation and Root Nodules
- Root Nodules Legume roots carry root nodules, special structures that house symbiotic nitrogen-fixing bacteria called rhizobia.
- 90% Fix Nitrogen About 90% of Fabaceae species can fix atmospheric nitrogen this way, converting it into a form the plant can use.
- Why It Matters This nitrogen-fixing ability is why legumes are widely used in crop rotation, replenishing soil fertility for the next crop planted in the same field.
- Other Members Beyond groundnut, horse-gram, and soybean, common Fabaceae members include beans, peas, lentils, chickpeas, and clovers.
Test Yourself
Previous Year Questions
- On identifying pea-family plants, asked as: “Consider the following plants: How many of the above belong to the pea family?” (UPSC CSP 2024, GS Paper I).
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