Hibiscus and Spirogyra are plants that are capable of producing their own food through photosynthesis. Cactus is also a plant that is capable of producing food, although it uses a specialized form of photosynthesis called CAM photosynthesis. On the other hand, Mushroom is not a plant and is not capable of producing its own food. It is a fungus that obtains its nutrients by decomposing organic matter. Therefore, Mushroom is the organism in the given options that is not a producer.