Question

why leaves in cactus are modified into spines​

Answer 1

Most species of cacti have lost true leaves, retaining only spines, which are highly modified leaves. As well as defending against herbivores, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of leaves, enlarged stems carry out photosynthesis.

Answer 2

Leaves in cactus are modified into spines to reduce transpiration