There are hundreds of alliums, including the onions and garlic we eat. The ornamental varieties often have leaves similar to onions, as well as the onion’s round ball shaped flower heads. However there are many varieties with star-like clusters of flowers and others, like A. Cernuum, the ‘Nodding Onion’, with hanging pendants of blossoms.
Alliums grow from bulbs. Allium bulbs may resemple onions, but it's the flowers you are after with these ornamental varieties. Alliums are easy to grow and are undemanding. They have strappy, undistinguished leaves and straight tubular flower stalks. The flower form in clusters and are best known in the round pom-pom form, but they can be start shaped, cup-shaped, semi-circular or pendulous.
My favorite allium is the globemaster. Its' 8" purple pom-pom head sticks almost three feet off the ground making a truly wonderful display in your garden or great for a spectacular cut arrangement.