Allium fistulosum, commonly called bunching onion, long green onion, Japanese bunching onion, scallion, spring onion, Welsh onion, is a species of perennial plant. The common name “Welsh onion” does not refer to Wales but derives from a near obsolete use of “Welsh” in the sense “foreign, non-native”, as the species is native to China, though cultivated in many places and naturalized in scattered locations in Eurasia and North America.

The species is very similar in taste and odor to the related common onion, Allium cepa, and hybrids between the two (tree onions) exist. The Welsh onion, however, does not develop bulbs, and possesses hollow leaves (fistulosum means “hollow”) and scapes. Large varieties of the Welsh onion resemble the leek, such as the Japanese negi, whilst smaller varieties resemble chives. Many Welsh onions can multiply by forming perennial evergreen clumps. Next to culinary use, it is also grown in a bunch as an ornamental plant.

Historically, the Welsh onion was known as the cibol. In Cornwall, they are known as chibbles.

fistulosumis not indigenous to Walesor particularly common in Welsh cuisine (the green Allium common to Wales is the leek, A. ampeloprasum, the national vegetable of Wales)