welsh onion (larger type of scallion)

It could also be Shallots, potato onion.

Where did it come from ?

Believe it or not, I got it from Home Depot. It was stuck in with some local provider with no name and looking quite scraggly. Haven't seen it since at the store. I wish it were a potato onion (do they grow in a ring like that?) but there are no onions under the surface. The "base" has a slight swelling like a regular long green onion. Where the roots are supposed to be looks a very little like the tuberose beginning of a chive root. It then goes on to have just a bunch of regular roots like a long green onion. By the way, when it "separates", it does it by letting a "shoot" out from the base of the stalk. It grows under the dry, silverish skin, bursts through, and eventually separates far enough from the parent to contribute to the circle shape.

I have the same thing in my garden. I took Publix (Grocery Store) green onions, chopped off the green part and planted the roots in my garden. They are now 31 inches in height (from soil) and 4 inches in circumfrance.