Coriander is a spice produced from the round, tan-colored seeds of the coriander plant (Coriandrum sativum), which is a member of the parsley family. The word coriander can be used to describe the entire plant: leaves, stems, seeds, and all.Coriander seeds, extract, and oils may all help lower blood sugar. In fact, people who have low blood sugar or take diabetes medication should practice caution with coriander because it’s so effective in lowering blood sugar.