Though it’s not clear why the coffee plant produces caffeine, it is believed to serve some essential role for the plant. We know this because caffeine is not part of the plant’s central metabolism and not use it to produce energy or new plant material. Therefore, it is called a secondary metabolite. Again, because it is found in all parts of the plant, from roots to leaves, and it takes energy to make, it must perform something essential. Here are the current theories: Allelopathic agent: produced by one plant to inhibit the growth of other plants. Although in labs the toxicity of caffeine to other plants has been demonstrated, it has not been observed or proven in nature. Defense against pets: it has been shown to be toxic to some insects and fungi. However, since there is yet to be a “caffeine deficient mutant coffee plant”, this has not been demonstrated in nature. Pollinator stimulant: research has shown that caffeine improves the memory of honey bees. Although, this has not been demonstrated in nature, and would not explain why caffeine is found in the root system.