Osmorhiza longistylis, Scented Sweet-cicely
The plant smells like licorice; the styles are longer than the petals at flowering time, or soon after.
Also see ontariowildflowers and missouriplants.

Osmorhiza claytonii, Bland Sweet-cicely
The plant is unscented; the styles are shorter than the petals, and remain short in fruit.
Also see ontariowildflowers.

Some sources say these can be separated by the hairiness of the stem, but this is unreliable.

Sources: The Flora of Delaware, William A. McAvoy, Janet Ebert, Manual of Vascular Plants.