Green manure refers to plants grown and then plowed under to improve soil fertility. Some plants are better suited as green manure than others.
To answer the question, the plant not normally used as green manure is Sida acuta. Sida acuta is not commonly used as a green manure crop because it has a low biomass production, and it's difficult to manage due to its bushy growth habit. On the other hand, the other three options (Mucuna utilis, Centrosema pubescens, and Pueraria phaseoloides) are commonly used as green manure crops due to their high biomass production, nitrogen fixation capacity, and easy management.