Flower:

The flower cluster of this goldenrod has broadly spreading panicles often arching down but sometimes somewhat erect, often as wide as it is tall and generally pyramidal in shape, and with up to 450 flower heads, sometimes more. Sometimes the whole cluster nods to one side.  Flowers are about ¼ inch across with usually 7 to 12 petals (ray flowers) surrounding a center disc with usually 8 to 15 disc flowers.

Surrounding the base of the flower are 3 or 4 layers of narrow, lance-linear, hairless yellowish-green bracts (phyllaries), the entire set of bracts (involucre) 3 to 4 mm (to 1/6 inch) long. The outer phyllaries are mostly pointed at the tip and the inner pointed to rounded. Flower stalks are longer or shorter than the involucre, all arranged on one side of the branch (secund) and curving upward, usually hairless, occasionally with scattered hairs.

Leaves and stems:

Leaves are both basal and alternate, hairless except for a fringe of short, fine hairs around the edges, the upper surface with a shiny luster though sometimes a slightly rough texture. Basal and lower stem leaves are up to 12 inches long and 2 inches wide, with broader lance-elliptic to spatula-shaped blades, pointed at the tip, tapering to a long, winged stalk, usually toothed around the edges. Lower leaves usually persist through flowering, have more than 3 major veins with the midvein prominent and the lateral veins either prominent or not.

Stem leaves become smaller as they ascend the stem, more lance-linear, stalkless, often toothless, and usually with clusters of small leaves (fascicles) in the upper axils. Lateral veins on the uppermost leaves are usually obscure with only the midvein prominent. Stems are erect to ascending, unbranched except in the flower cluster, typically smooth throughout though very fine, short hairs may be present in the cluster branches and/or a few hairs scattered lower on the stem. Stems are single to several in a group from underground elongating rhizomes, often forming small, loose colonies of flowering plants mixed with basal leaf clumps of non-flowering plants, sometimes forming larger colonies.

Fruit:

Fruit is a brown, sparsely hairy, oblong to narrowly cone-shaped seed (achene) 1 to 1.5 mm long, with a tuft of light brown hairs (pappus) 2.5 to 3.5 mm long attached at the tip to carry it off in the wind.

Notes:

Early Goldenrod reaches the western edge of its range in Minnesota and is primarily found north of the seven county Metro area. As its common name suggests, it begins flowering earlier than just about all others, as early as mid to late June where most others do not start until mid to late July or even August. While this can be an aid in identification early in the season, other characteristics must be focused on when other Goldenrods enter into the fray.

For Early Goldenrod, look for a shorter plant (typically not more than 3 feet tall), clumps of stalked basal leaves, lower stem leaves with winged stalks, significantly smaller, stalkless upper stem leaves usually with clusters of small leaves in the upper axils. The flower cluster is typically pyramidal in shape but may nod to one side. Leaves are usually toothed, sometimes not; likewise leaf veins may be prominent or not, but usually more prominent on lower and basal leaves. Veins on lower leaves tend to number more than 3 but on upper leaves usually only the midvein is prominent. The entire plant should be hairless except for a fine fringe of hairs on leaf edges, and sometimes sparse fine hairs on flower stalks and branches, and/or occasionally the stem. With a nodding flower cluster, the overall form may resemble Gray Goldenrod (Solidago nemoralis), but it is hairy all over and doesn't bloom until August.

The only other Minnesota Goldenrod that shares the same traits is Missouri Goldenrod (Solidago missouriensis) and it can be very difficult to tell them apart. I'm about ready to give up, myself. Like S. juncea, S. missouriensis tends to bloom earlier than other Goldenrods but about 2 weeks or so later than S. juncea, though there is significant overlap. S. juncea flower clusters often to nod to one side; S. missouriensis sometimes has flowers that are not secund on a branch. S. missouriensis is noted to have only 3 prominent veins (midvein and a pair of lateral veins) on most leaves (often looks like 5 to me) where S. juncea supposedly has more, but at least one reference notes S. juncea lateral veins are obscure, not prominent, and doesn't specifically distinguish upper vs. lower leaves. Lower leaves on S. juncea tend to persist through flowering and may drop off from S. missouriensis, but that's not always the case. After comparing lower leaves on dozens of herbarium specimens, I concluded that the veins on both are all over the map, virtually the same in a number of cases and not consistent enough to be a reliable diagnostic trait, at least for Minnesota populations. Your own observations may be different, but that's my take on it.

Habitat may be more helpful, with S. missouriensis mostly found in open sandy prairie, savanna or dunes, and less often on bluffs, gravelly roadsides or open woods, where S. juncea is more often found on gravelly roadsides, bluffs, rocky shores, outcrops, Jack pine forests and trail edges (often in disturbed soils), and less often in open prairies or meadows. S. missouriensis also has been recorded across most of the state and tends to form larger colonies with 40+ stems, where S. juncea is absent from our western and southern counties, and more typically forms looser colonies with fewer than 10 stems.