Why do cactuses have green stems?
gives cactus stems their green color. A cactus has chlorophyll because of the stem’s photosynthetic interaction with sunlight to make cactus foods. In many other plants, photosynthesis takes place in the leaves. But cactus needles don’t offer a large enough surface for photosynthesis to take place or for photosynthetic byproducts to be stored. Instead, needles have reduced surface areas to stop surface evaporation of moisture. So photosynthesis instead must take place within the larger surface area of the stem.
