[5] Giant sumpweed is believed to be native to the Great Plains but is now found across much of southern Canada and the contiguous United States, though rarely in the Southeast.

[8] It has been introduced and semi-naturalized in central and southern Britain, partly via seeds bought for bird food.

The leaves are long-stalked and double-toothed with rough hairs on the top, and light green and fuzzy on the bottom.

The staminate florets have stamens with the filaments fused into a tube and the anthers free but closely arranged in a ring.

The pistillate florets have stamens with the filaments into a tube and the anthers free but closely arranged in a ring.

[4][7] The fruit is an egg-shaped achene, dark brown to nearly black, 2 to 3 mm (1⁄16 to 1⁄8 in) long, with a tuft of hairs attached to one end.