- A Stem tendril
- B Stem spine (thorn)
- C Phylloclade
- D Cladode
Correct answer: B. Stem spine (thorn)
Explanation: Bougainvillea has stem modifications into hard, sharp thorns (spines) that are modified axillary buds or stems. They provide defense. Contrast with leaf-spine (cactus) and prickle (rose - epidermal outgrowth).
Concept context
External structure of roots, stems, and leaves plus internal tissue organization. High marks in Class 11 and NEET.