WordNet sense 1 (common weedy European plant introduced into North America; often used as a potherb):

lamb's-quarters, wild spinach, Chenopodium album

WordNet sense 2 (leaves sometimes used as potherbs; seeds used as cereal; southern United States to Central America; India and China):

Amaranthus hypochondriacus

WordNet sense 3 (leaves collected from the wild):

lamb's-quarter