onion used both as a general term, applying to many members of the extensive genus Allium, and as a specific one referring to regular round (globe) onions of the species Allium cepa. The box shows what other entries there are, and how the botanical species relate to common names. Of the names shown in the box, the ones which constantly cause confusion are spring onions and scallions. Usage varies to such an extent that no generally valid definitions can be given.
The present entry is concerned with mature onions of the species A. cepa. The original wild ancestor of this, the common onion, has long since disappeared; but related wild species still grow in C. Asia. The whole diverse onion family evidently arose in this area, although it is now disseminated throughout the world.
