Onion: Allium Species

A. cepa includes all the common western round (globe) onions with single bulbs, which in their immature state are used as spring onions in Britain; the ‘aggregate’ onions with multiple (underground) bulbs such as the shallot, the ‘ever ready’, and ‘potato’ onions; and also the tree onions (also known as Egyptian or ‘top-set’ onions), which reproduce by forming miniature self-planting bulbs on top of the stem, e.g. the variety Catawissa. Both the last two groups can be referred to as ‘multiplier’ onions.