A. giganteum is a perennial with spreading, glossy, strap-shaped basal leaves which die down before the flowers. Dense globose umbels of bright purple flowers are borne on tall stems in summer
The name Allium is from the ancient name for garlic, which is part of the genus. There are estimated to be around 700 species within the genus, and many cultivars. There are perennials and biennials, ranging in height from 10cm - 1.5m (4in - 5ft) or more.
They are mainly from dry and mountainous areas, all from the Northern Hemisphere, and they have adapted to live in almost every plant habitat on the planet, from ice cold tundra to burning, arid deserts.
Many members of the genus give themselves away with the distinctive smell of onions when the bulb or foliage is bruised.
They have upright to spreading linear-shaped leaves. The tubular based flowers are bell, star or cup shaped which are borne in spherical umbels 1 - 10cm (3/8 - 4in) across.
In most species, a single bulb produces clusters of offset bulbs around it, which gradually form clumps.
Taller species look good in groups in a border. The flower heads dry well. Several species have culinary uses, including A. sativum (garlic), culinary onions, shallots and chives.
The whole group was prized by the ancients as possessing medical and aphrodisiac qualities as well as flavour. The Romans are sometimes held responsible for their wide distribution by taking them wherever they went.