UPSC Prelims 2024 Q19: Pea Family (Fabaceae) Crops — Explained
Consider the following plants:
1. Groundnut
2. Horse-gram
3. Soybean
How many of the above belong to the pea family?
- Only one
- Only two
- All three
- None
Answer: (c) All three
Statement-wise explanation
- 1: correct — Groundnut (Arachis hypogaea) belongs to the family Fabaceae, also called Leguminosae or the pea family. It is grown as an oilseed, but botanically it is a legume. Its flowers have the butterfly-shaped (papilionaceous) form of the family. After fertilisation, a stalk called the peg pushes the developing pod into the soil, so the 'nut' is really an underground legume pod.
- 2: correct — Horse-gram (Macrotyloma uniflorum), also called kulthi, is a pulse in the family Fabaceae. It is a hardy, drought-tolerant kharif legume of the semi-arid south and east of India. Like other legumes, it carries root nodules with nitrogen-fixing bacteria.
- 3: correct — Soybean (Glycine max) is a member of the family Fabaceae. India counts it as an oilseed, and its seed is rich in both protein and oil. It is still a legume: it bears pods and forms Rhizobium root nodules that fix atmospheric nitrogen.
How to eliminate
This question tests a fact you either know or don't. The trap is how the crops are grouped in Indian farm statistics: groundnut and soybean are listed as oilseeds, not pulses, so many candidates leave them out of the 'pea family' and pick 'only one'. That grouping is about how the crop is used. It says nothing about the plant's botany. Here is a shortcut that works: if a crop bears its seeds in a pod that splits along two seams, it is almost certainly a legume. Gram, pea, beans, lentil, groundnut, soybean, horse-gram and guar all do. Fact to remember: groundnut and soybean are legumes grown for oil, and horse-gram is a legume grown as a pulse. All three belong to Fabaceae.
Know more
The pea family: Fabaceae (Leguminosae)
Fabaceae is one of the largest families of flowering plants, with roughly 20,000 species. Members share three traits:
- Fruit: a legume (pod) that splits along two seams.
- Flower: in the main subfamily, the flower is butterfly-shaped (papilionaceous), with a standard petal, two wing petals and a keel.
- Root nodules: most members host Rhizobium-type bacteria. These bacteria turn atmospheric N₂ into ammonia through the enzyme nitrogenase. This is why legumes are used in crop rotation, intercropping and green manuring to restore soil nitrogen.
Economic grouping vs botanical family
| Crop | Botanical name | Family | Indian crop group |
|---|---|---|---|
| Groundnut | Arachis hypogaea | Fabaceae | Oilseed |
| Soybean | Glycine max | Fabaceae | Oilseed |
| Horse-gram | Macrotyloma uniflorum | Fabaceae | Pulse |
| Red gram (arhar/tur) | Cajanus cajan | Fabaceae | Pulse |
| Bengal gram (chana) | Cicer arietinum | Fabaceae | Pulse |
| Guar (cluster bean) | Cyamopsis tetragonoloba | Fabaceae | Vegetable / industrial gum |
| Mustard | Brassica spp. | Brassicaceae | Oilseed |
| Sunflower | Helianthus annuus | Asteraceae | Oilseed |
| Sesame | Sesamum indicum | Pedaliaceae | Oilseed |
Related facts UPSC likes to test
- Some legumes are trees: tamarind, Indian rosewood (Dalbergia), Acacia and Prosopis.
- Geocarpy: the groundnut's pod ripens underground. This is why the crop needs light, loose, well-drained soil.
- Pulses are the dried edible seeds of legumes. Every pulse is a legume, but not every legume is a pulse. Soybean and groundnut are counted as oilseeds.
NCERT Concepts to Revise
- Groundnut: Statement 1 hinges on whether groundnut's 'oilseed' label tells you anything about its botanical family.
- Soybean: Statement 3 tests soybean, which India counts as an oilseed although it is a protein-rich podded crop.
- Oilseeds: The question's trap is mixing up an economic crop group like oilseeds with a botanical family.