| Tree onion | |
|---|---|
 | |
| Onion stalks withbulblets, or miniature onions grown at the top of the stalk | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Monocots |
| Order: | Asparagales |
| Family: | Amaryllidaceae |
| Subfamily: | Allioideae |
| Genus: | Allium |
| Species: | A. × proliferum |
| Binomial name | |
| Allium× proliferum | |
| Synonyms[1] | |
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Thetree onion (Allium ×proliferum) is aperennial plant similar to thecommon onion (A. cepa), but with a cluster of bulblets where a normal onion would have flowers. Tree onions are also known asSpring onions,Green onions,topsetting onions,walking onions, orEgyptian onions. Genomic evidence has suggested that they may be adiploid hybrid of theshallot and theWelsh onion (A. fistulosum).[2][3][4] Other sources treat the tree onion asA. cepa var.proliferum orA. cepa Proliferum Group.
Tree onion bulblets will sprout and grow while still on the original stalk. The bulblets are usually marble-sized, between 0.5 cm to 3 cm in diameter. They 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" derived fromRomani people[5] bringing tree onions to Europe from the Indian subcontinent. The phenomenon of forming bulblets (bulbils) instead of flowers is also seen in top-settinggarlic and other alliums, which sometimes may also be referred to as top onions or tree onions.[6]
Also known as turfed stone leek, it may be cultivated commercially and for foliage.[7][8] It is described as a shallot which can be grown in tropical conditions.[9]
Many tree onions are very strong flavoured, although some cultivars are relatively mild and sweet.[5] The underground bulbs are particularly tough-skinned and pungent,[10] and can be quite elongate, likeleeks,[10] or in some types may form bulbs up to 5 cm across.[5] Young plants may be used asscallions in the spring, and the bulblets may be used in cooking similarly to regular onions, or preserved bypickling.[10]
The plant is known aswakegi (ワケギ) "split scallion" in Japan. Considered a specialty of theHiroshima Prefecture, it is used in local cooking similar to other scallions.[11]
In Korea,Allium ×proliferum along withA. fistulosum is calledpa (파, "scallion"), while commononions are calledyangpa (양파, "Western scallion"). WhileA. ×proliferum is calledjjokpa (쪽파, "separated scallion"),A. fistulosum is called eitherdaepa (대파, "big scallion") orsilpa (실파, "thread scallion") depending on the size. Unlikedaepa andsilpa, which are usually used as a spice, herb, or garnish,jjokpa is often used as the main ingredient of various scallion dishes inKorean cuisine. Common dishes made withjjokpa includepajeon (scallion pancakes) andpa-kimchi (scallion kimchi).[citation needed]
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A few alliums, such as A. roseum and A. sphaerocephalon produce aerial bulbils in the flower head.
