Concept: This question tests your understanding of plant modifications, specifically the concept of a phyllode, which is a modification of the petiole.

Why (D) is correct: In Australian Acacia (e.g., Acacia auriculiformis), the true leaves are small and fall off early. The petiole expands, becomes flattened, green, and performs photosynthesis, functioning like a leaf. This modified petiole is called a phyllode.

Why other options are wrong:

• (A) Opuntia: Has flattened, fleshy stems called phylloclades, and leaves are modified into spines.
• (B) Asparagus: Has modified stems called cladodes (small, needle-like photosynthetic structures).
• (C) Euphorbia: Many species have succulent stems and reduced leaves; some have phylloclades, but not phyllodes.

Common Mistake: Students often confuse phyllodes (modified petioles) with phylloclades or cladodes (modified stems).

NEET Tip / Mnemonic: Remember 'Acacia' for 'Acacia' and 'phyllode' for 'petiole modification'.

Correct Answer: (D)