What is the physical difference between Bok Choy stalks and leaves when cooking?

Stalks are firmer and require slightly longer cooking than the tender leaves

The structure of bok choy presents a practical consideration during preparation because its two main components cook at disparate rates. The vegetable is characterized by firm, water-storing stalks at the base and more delicate, dark green leaves attached above. Due to their inherent density and crispness, the stalks possess a crunchier texture and necessitate slightly extended cooking times to reach optimal tenderness. In contrast, the leaves are substantially more delicate and wilt very rapidly when exposed to heat, meaning they require only brief cooking periods. This difference mandates timing adjustments during cooking to ensure neither the stalks remain undercooked nor the leaves become overly soft.