| Tree onion | |
|---|---|
| Onion stalks with bulblets, or miniature onions grown at the top of the stalk. | |
| Scientific classification | |
| Kingdom: | Plantae |
| clade: | Angiosperms |
| clade: | Monocots |
| Order: | Asparagales |
| Family: | Amaryllidaceae |
| Subfamily: | Allioideae |
| Genus: | Allium |
| Species: | A. ×proliferum |
| Binomial name | |
| Allium ×proliferum (Moench) Schrad. ex Willd. |
|
Tree onions, Allium ×proliferum, are similar to common onions, but with a cluster of bulblets where a normal onion would have flowers. Genomic evidence has conclusively shown that they are a hybrid of the common onion (A. cepa) and the Welsh onion (A. fistulosum).[1] However, some sources may still treat the tree onion as A. cepa var. proliferum or A. cepa Proliferum Group. They are also commonly called top onions, topsetting onions, walking onions, or Egyptian onions. Tree onion bulblets will sprout and grow while still on the original stalk, which may bend down under the weight of the new growth and take root some distance from the parent plant, giving rise to the name walking onion. It has been postulated that the name Egyptian onion is derived from tree onions being brought to Europe from the Indian subcontinent by the "Gypsies".[2]
The phenomenon of forming bulblets instead of flowers is also seen in garlic and other various species of Allium, which sometimes may also be referred to as top onions or tree onions. The bulblets are generally marble-sized, usually within .5 cm to 3 cm in diameter, although sizes may differ out of this range from time to time.
Many Egyptian onions are very strong flavoured, although some cultivars are relatively mild and sweet.[2] The underground bulbs are particularly tough-skinned and pungent,[3] and can be quite elongate, like giant scallions or leeks,[3] or in some types may form bulbs up to two inches across.[2] Young plants may be used as scallions in the spring, and the bulblets may be used in cooking similarly to regular onions, or preserved by pickling.[3]