What structures are found in pairs at the base of each spikelet?

The structures found in pairs at the base of each spikelet are glumes. Glumes are specialized bracts that serve protective roles for the developing spikelet and are an essential component of the inflorescence in grasses. They typically come in pairs, one on each side, and are located at the base of the spikelet itself. Their main function is to shield the florets within the spikelet from environmental factors and predation, contributing to the overall reproductive success of the plant.

While petals, bracts, and leaflets all have roles in the structure and function of flowering plants, they do not specifically form paired structures at the base of spikelets. Petals are part of flowers and not relevant to spikelets. Bracts can be associated with flowers or inflorescences but do not always appear in pairs at the spikelet base. Leaflets, being part of compound leaves, are also not related to spikelets in grasses. Therefore, glumes are uniquely suited to the specific context of spikelets, making them the correct answer.