Early Goldenrod (Solidago juncea)

I am going to first say that identifying goldenrods are very difficult. With that being said, you might want to bring an experienced botanist (por ejemplo yo)  along with you to identify goldenrods.

From my own observations, early goldenrod is identified by being the first goldenrod to bloom. It blooms from mid-late August to late September, while the other goldenrods bloom from mid-late September all the way until early November. If you notice the flower, some of the flower stems branch out in almost a 90 angle. This is characteristic of this plant. All of the other goldenrods branch at different angles, usually around 45 degrees. Again, this is from my own observations, some other people may have different ways of classifying this plant.