Mature seeds of Melilotus indicus (L.)All. are considered as one of the hardest leguminous seeds that develop inside single- seeded small pods. The young ovary is covered with small, multi-celled uni-seriate glandular trichomes that persist long up to the dicotyledonous embryo stage, at a time when seed coat is hard enough. During ontogeny the outer integument modifies gradually into a thick and hard seed coat composed of outermost, palisade like, macro-sclereid layer, a hypodermal osteo-sclereid layer followed by two to three parenchymatous layers. Like other legumes, the macro-sclereid layer represents the  modified epidermis of the outer integument while the cells of its hypodermal layer change to osteo-sclereids imparting additional hardness to the seed coat. The tight packaging and cuticularization of macro-sclereids make the seeds of Melilotus indicus hard and impermeable to water. The inner integument does not participate in seed coat formation instead helps provide nutrition to the developing embryo before its lyses. The mature dry seed is dorsal-ventrally flat with a complex hilar region.