tree onion

{{Short description|Species of flowering plant}}

{{Use dmy dates|date=August 2022}}

{{Speciesbox

| genus = Allium

| species = {{hybrid}} proliferum

| name = Tree onion

| image = Allium fistulosum bulbifera0.jpg

| image_caption = Onion stalks with bulblets, or miniature onions grown at the top of the stalk.

| authority = (Moench) Schrad. ex Willd.

| synonyms_ref = {{The Plant List}}

| synonyms = {{Species list

|Allium cepa var. proliferum|(Moench) Regel

|Allium fistulosum var. viviparum|Makino

|Allium fistulosum f. viviparum|(Makino) M.Hiroe

|Allium multitabulatum|S. Cicina

|Allium multitabulatum|S. Cicina

|Allium × wakegi|Araki

|Cepa × prolifera|Moench

}}

}}

The tree onion (Allium × proliferum) is a perennial plant similar to the common onion (A. cepa), but with a cluster of bulblets where a normal onion would have flowers. Tree onions are also known as topsetting onions, walking onions, or Egyptian onions. Genomic evidence has suggested that they may be a diploid hybrid of the shallot and the Welsh onion (A. fistulosum).{{cite journal |author=Friesen, N. & M. Klaas |year=1998 |title=Origin of some vegetatively propagated Allium crops studied with RAPD and GISH. |journal=Genetic Resources and Crop Evolution |volume=45 |issue=6 | pages=511–523 |doi=10.1023/A:1008647700251 |s2cid=26205471 }}{{cite journal|last1=Yamashita|first1=Kenichiro|last2=Tashiro|first2=Yosuke|title=RFLP Analysis of Mitochondrial DNA in Wakegi Onion.|journal=Engei Gakkai Zasshi|date=2001|volume=70|issue=2|pages=232–234|doi=10.2503/jjshs.70.232|doi-access=free}} {{cite book|author=James L. Brewster|title=Onions and Other Vegetable Alliums|url=https://archive.org/details/Onions_and_Other_Vegetable_Alliums_Crop_Production_Science_in_Horticulture_by_Ja|date=1 January 2008|publisher=CABI|isbn=978-1-84593-622-8|pages=[https://archive.org/details/Onions_and_Other_Vegetable_Alliums_Crop_Production_Science_in_Horticulture_by_Ja/page/n163 152]–3}} Other sources treat the tree onion as A. cepa var. proliferum or A. 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 from Romani people{{cite web |url=http://www.garden.org/articles/articles.php?q=show&id=1727&page=4 |title=Confessions of an Onion Addict |last=Ruttle |first=Jack |publisher=National Gardening Association |access-date=17 February 2011}} bringing tree onions to Europe from the Indian subcontinent. The phenomenon of forming bulblets (bulbils) instead of flowers is also seen in top-setting garlic and other alliums, which sometimes may also be referred to as top onions or tree onions.{{cite web|url=https://piedmontmastergardeners.org/article/allium-a-whimsical-accent-for-the-ornamental-garden/|quote=A few alliums, such as A. roseum and A. sphaerocephalon produce aerial bulbils in the flower head.|title=Allium | Piedmont Master Gardeners }}

Also known as turfed stone leek, it may be cultivated commercially and for foliage.{{cite book|author1=Haim D. Rabinowitch|author2=Lesley Currah|title=Allium Crop Science: Recent Advances|url=https://books.google.com/books?id=wGmBCwAAQBAJ&pg=PA87|year=2002|publisher=CABI|isbn=978-0-85199-510-6|pages=87–8}}{{cite book|author1=Vincent E. Rubatzky|author2=Mas Yamaguchi|title=World Vegetables: Principles, Production, and Nutritive Values|url=https://books.google.com/books?id=2I_uBwAAQBAJ&pg=PA307|date=6 December 2012|publisher=Springer Science & Business Media|isbn=978-1-4615-6015-9|pages=307–8}} It is described as a shallot which can be grown in tropical conditions.{{cite book|author1=Jaime Prohens-Tomás|author2=Fernando Nuez|title=Vegetables II: Fabaceae, Liliaceae, Solanaceae, and Umbelliferae|url=https://books.google.com/books?id=CD_OLc3lYDMC&pg=PA124|date=6 December 2007|publisher=Springer Science & Business Media|isbn=978-0-387-74110-9|pages=124, 152}}

Many tree onions are very strong flavoured, although some cultivars are relatively mild and sweet. The underground bulbs are particularly tough-skinned and pungent,{{cite web |url=http://counties.cce.cornell.edu/schenectady/Master%20Gardener%20Website/projectdocs/factsheets/vegetables/Egyptian%20Onions.pdf |title=Egyptian Onions are the Easiest |last=Chandoha |first=Walter |publisher=Cornell University Cooperative Extension |access-date=26 April 2011}} and can be quite elongate, like leeks, or in some types may form bulbs up to 5 cm across. 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.