Flax seeds and flowers. Flax (Linus usitatissimum) seeds are the source of linseed, which is rich in omega 3 oils. As such, the seeds or their oils are often taken as a dietary supplement. The plant has long been used in herbal medicine as a laxative, and infusions have been used to treat coughs. Cover credit: BILDAGENTUR-ONLINE/TH FOTO/SCIENCE PHOTO LIBRARY.