Green plants are called producers simply because they synthesize their food through a process referred to as photosynthesis. The photosynthesis process works in such a way that an organism manufactures its own food from carbon dioxide and water, which are simple inorganic substances, and this is done in the presence of chlorophyll, making use of sunlight.
Organisms that have the ability to undergo this process, or better still, organisms that undergo this process of photosynthesis are called producers. Thus, generally, green plants are described as producers. This concept is also very similar to the concept of a producer in commerce or the commercial world.
The green plants serve as a source of food for other organisms, which can make us describe them as the organisms that produce for other organisms. Other organisms that feed on them directly or indirectly are referred to as consumers and decomposers.