Question

the stem in cactus is green with several spines but no leaves why​

Answer 1

the spikes of cactus prevent the cactus from loosing water or to survive in extreme climates

Answer 2

Answer:

the stem of cactus has spine but not leaves because the leaves are reduced into spines as the cactus grows in desert ecosystem it won't have enough water to perform photosynthesis .So it is reduced into spines as lesser amount of photosynthesis takes place using the green pigment chlrophyll present in stems

Hope this answer helps you