The shapes and sizes of amaranth species vary, but they all have medium to large sized alternating simple oval-shaped leaves and stems with some red coloration. A number of upright varieties like Palmer pigweed (A. palmeri) and smooth pigweed (A. hybridus) can grow 3 to 10 feet (1 to 3 meters) tall with stout stems. However, the prostrate pigweed (A. graecizans) grows close to the ground and has smaller leaves. The greenish flowers of amaranth plants form a dense cluster at the tops of the plants of the upright varieties or among the leaves of the prostrate pigweed. The lens-shaped amaranth seeds are dark brown or black colored in weedy species and light-colored in domestic species.