Flower:

Flower clusters are variable in shape, from broadly pyramidal with arching branches to more upright with ascending branches, small to medium size, with up to 210 flower heads, sometimes more. Flowers are about 1/8 inch across with 5 to 14 petals (ray flowers) surrounding a center disc with 8 to 20 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) 2.5 to 4.5 mm (to 1/6 inch) long. The outer phyllaries are pointed to rounded at the tip and the inner mostly rounded. Flower stalks are about as long as or slightly longer than the involucre, hairless or with a few sparse hairs, usually all arranged on one side of the branch (secund) and curving upward, sometimes arranged on all sides of a branch.

Leaves and stems:

Leaves are both basal and alternate, hairless except for a fringe of short, fine hairs around the edges, usually with 3 prominent veins, though larger leaves may have an extra pair of somewhat fainter lateral veins. Basal and lower stem leaves are toothless to finely toothed around the edge, lance-elliptic to spatula-shaped, pointed at the tip, the blade up to about 4½ inches long and ¾ inch wide, with a long taper to winged stalk nearly as long as the blade. Leaves near the base may wither away by flowering time.

Stem leaves become smaller as they ascend the stem, more elliptic to lance-linear, stalkless, often toothless, the upper leaves often becoming abruptly much smaller with clusters of small leaves (fascicles) in the axils. Mid to upper leaves usually have 3 prominent veins though the uppermost leaves may have just a prominent midvein. Stems are erect to ascending, often red especially towards the base, 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 a few to many (40+) in a group from slender underground rhizomes, often forming large colonies of flowering plants mixed with basal leaf clumps of non-flowering plants, though the flowering plants are usually more numerous.

Fruit:

Fruit is a brown, sparsely hairy, oblong to narrowly cone-shaped seed (achene) 1 to 2 mm long, with a tuft of light brown hairs (pappus) 2.5 to 3 mm long attached at the tip to carry it off in the wind.

Notes:

Missouri goldenrod is a highly variable species found throughout much of Minnesota and westward. It prefers dry sandy, open prairie where it often produces large spreading colonies. It is one of the earlier blooming Goldenrods in Minnesota, usually starting by mid-July.

For Missouri Goldenrod, look for a shorter plant (typically under 3 feet tall), at least some clumps of stalked basal leaves, usually red stems, lower stem leaves with winged stalks, significantly smaller, stalkless upper stem leaves usually with clusters of small leaves (fascicles) in the upper axils. The flower cluster is typically pyramidal in shape with flowers all on one side of a branch (secund) but sometimes branches are more ascending with flowers on all sides of a branch. Leaves are toothed or not, and sometimes very narrow. There are usually 3 prominent leaf veins, though larger leaves may look like 5 (a pair of lateral veins from the base and another pair about mid-blade). 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. The overall form and hairlessness may resemble Giant Goldenrod (Solidago gigantea), which is a larger plant (over 3 feet), has no basal leaves, upper stem leaves are not much smaller than mid-stem leaves, lower leaves always wither by flowering, and doesn't bloom until August.

The only other Minnesota Goldenrod that shares the same traits is Early Goldenrod (Solidago juncea) 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 (larger ones may have 5) 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.