blue-stem goldenrod, aka wreath goldenrod
As I wrote previously (and last year), goldenrod identification can get really tricky. Both zigzag goldenrod and blue-stem goldenrod have unusual characteristics, though. For one thing, they’re woodland plants (most goldenrods like full sun, or at least more sun). And they bloom relatively late. And few other goldenrod species have flower clusters in the leaf axils; most goldenrods have terminal, or at least upper-stem, inflorescences.
Whereas zigzag has big, oval, serrated mid-stem leaves, bluestem has linear, smooth-edged or serrated, one-nerved leaves that are sessile, all the way along the stem, which may or may not carry a slight blue tint. Better to rely on leaf shape and the presence of axillary flowers for identification. As you can see from the photos, it will sometimes have an upright habit, but more often flops over under the weight of the blossoms.
The specific epithet is from the Latin caesius, meaning cutting or piercing.
Blue-stem goldenrod can be found from Texas in the south and northeastward into Quebec. It’s endangered in Wisconsin.