Why are banana leaves so big?
Similarly, it is asked, why do banana trees have big leaves?
Large-leaved plants like bananas and palms tend to live in the tropics, while small-leaved plants like heather and clover are found closer to the poles. But large leaves absorb more of the sun's heat and get hotter than small ones, suggesting they should be found in cold regions, not the tropics.
Keeping this in view, why are rainforest leaves so big?
Large leaves are also poorly adapted to hot desserts, because they tend to overheat during the day. Large leaves also allow tropical plants to capture more sunlight energy and together with a ready supply of water are able to convert this energy readily into rapid growth.
It comes down to the risk of overheating or freezing. Plants have a delicate balance to strike when it comes to their leaves. They need to be large enough to absorb lots of sunlight for photosynthesis, but not so big they use up a lot of water to cool those leaves through evaporation.