Concept:Pasture grasses are true grasses, while legumes are not pasture grasses.
Explanation:Pennisetum purpureum, Axonopus compressus, and Panicum maximum are all pasture grasses commonly used for livestock grazing.
They belong to the grass family and serve as forage grasses.
Stylosanthes gracilis is a tropical forage legume, not a grass.
Although it is also used as animal feed, it does not belong to the grass family.
Therefore, it is the plant that is not a pasture grass.
Answer:C. Stylosanthes gracilis