Find odd one out w.r.t. green manures Melilotus Crotalaria Jatropha Trifolium

The correct option is 3.
Jatropha is a genus of flowering plants in the spurge family, Euphorbiaceae. The name is derived from the Greek words iatros, meaning "physician," and trophe, meaning "nutrition," hence the common name physic nut. It contains approximately 170 species of succulent plants, shrubs and trees (some are deciduous, like Jatropha curcas). Most of these are native to the Americas, with 66 species found in the Old World. Plants produce separate male and female flowers. As with many members of the family Euphorbiaceae, Jatropha contains compounds that are highly toxic.