Tree onions are a strong-growing onion with a bunch of bulblets where a normal onion would have flowers. They are members of the "proliferum" cultivar of the onion (Allium cepa), and are also commonly called Top Onions, Topset Onions, Walking Onions, or Egyptian onions. In some varieties these bulblets will sprout and grow while still on the original stalk, which may bend down under the weight of the new growth, giving rise to the name, walking onion. While these onions are often listed as Allium cepa var. proliferum, recent research has shown that the tree onion is a cross between Allium cepa, the cultivated onion, and Allium fistulosum, the Welsh onion. The Royal Horticultural Society currently treats it as Allium cepa Proliferum Group. This phenomenon of forming bulblets instead of flowers is also seen in garlic and other various wild species of Allium. A similar relative to the tree onion is the pearl onion.