As nouns the difference between goldenrod and goldenseal

is that goldenrod is any tall-stemmed plant principally from genus Solidago (also genus: Oligoneuron), usually with clusters of small yellow flowers while goldenseal is species: Hydrastis canadensis, a perennial herb of the buttercup family, native to southeastern Canada and the northeastern United States, with a thick, yellow knotted rootstock and diverse medicinal properties.

As an adjective goldenrod

is of a golden-yellow colour, like that of the goldenrod plant.