I agree with everything enigma has said. English "scallion" is a collective term, ein Sammelbegriff. Not only the Wikipedia article he cites, but the various dictionaries cited above so indicate.
In addition to the current LEO-entry enigma cites, but all current LEO-entries for "scallion":
Siehe Wörterbuch: scallion• scallion sg., usually in plural: scallions [bot.] = die Frühlingszwiebel meist im Pl.: Frühlingszwiebeln
• scallion [bot.] = Grüne Zwiebel
• scallion sg., usually in plural: scallions [bot.] = die Jungzwiebel meist im Pl.: Jungzwiebeln (Österr.)
as well as the current LEO-entries for "green onion":
Siehe Wörterbuch: green onion• green onion sg., usually in plural: green onions = die Frühlingszwiebel meist im Pl.: Frühlingszwiebeln
• green onion sg., usually in plural: green onions = die Jungzwiebel meist im Pl.: Jungzwiebeln (Österr.)
I suggest new or replacement entries as indicated above.
@enigma, I try to avoid proposing grocery store vegetables because of confusion & regional names just like this. Other confusing names I have avoided proposing include different types of lettuce, tomatoes, capsicum peppers, & a long list of relatives of mustard & cabbage, even though I consume great quantities of them at the dinner table (preferrably fresh, from my own garden). :-)
As for Frühlingszwiebel & Jungzwiebel, see:
Siehe auch: Welsh onion - die Winterheckenzwiebel, wiss.:...Siehe Wörterbuch: Allium fistulosum
