Acalypha rhomboidea, Rhomboid Copperleaf
Most leaf stalks are more than half as long as the leaf; the leaves are about half as wide as long. The stem is covered with short, curved hairs.

Acalypha virginica, Virginia Copperleaf
Similar to the common species, but the leaf stalks are less than half the length of the leaf, and the stem has some long hairs in addition to the short ones.

Acalypha gracilens, Slender Copperleaf
Leaves are narrow, on very short stalks. The stem is covered with very short hairs only.

Sources: The Flora of Delaware, Herbaceous Plants of Maryland.