Flower:

Branching clusters of numerous small, stalked, yellow flower heads at the top of the plant. Cluster shape is variable, from pyramidal (as long as or longer than wide) to broadly spreading and cascading (wider than long), sometimes more compact and club-shaped on smaller plants, and with 100 to 1300+ flowers in the cluster. Flowers are about 1/8 inch across with usually 8 to 15 petals (ray flowers) surrounding a center disc with usually 3 to 6 disc flowers.

Surrounding the base of the flower are 3 or 4 layers of narrow, lance-linear, hairless green bracts (phyllaries), the entire set of bracts (involucre) usually 2 to 3 mm (to 1/8 inch) long. Flower stalks are hairy, as long as or slightly longer than the involucre, all arranged on one side of the branch (secund) and curving upward.

Leaves and stem:

Leaves are all alternate without a basal rosette, relatively thin and lax, strongly 3-nerved, 2 to 7½ inches long, ¼ to 1¼ inches wide, mostly lance-elliptic and broadest near the middle, tapering to a sharp point at the tip and tapering to a stalkless base. Edges are mostly sharply toothed except near the leaf base, though leaves may be toothless or nearly so just below the flower cluster. Leaves are largest around mid-stem, somewhat smaller above, and lower stem leaves often withered away by flowering time.

The upper surface is smooth to slightly rough, the lower hairless or more commonly short-hairy along major veins, sometimes minutely hairy on the lower surface as well as the veins.

Stems are erect and rigid, short hairy from the flower cluster to about mid-stem, then sparsely hairy to hairless toward the base. Insect galls are not present on stems. Stems are single or up to 20+ stems in a group from underground creeping rhizomes.

Fruit:

Fruit is a brown, sparsely hairy, oblong to narrowly cone-shaped seed (achene) 1 to 1.5 mm long, with a tuft of whitish hairs (pappus) 1.8 to 2.2 mm long attached at the tip to carry it off in the wind.

Notes:

The “Canada Goldenrod complex” in Minnesota consists of Solidago canadensis, S. altissima, and S. gigantea (related S. missouriensis and S. juncea are not technically included but are also similar except have basal leaves). They can be a tough group to crack.

Canada Goldenrod and the closely related Tall Goldenrod (S. altissima) are very similar and both have two recognized varieties or subspecies; the two of Canada Goldenrod are var. canadensis and var. hargeri, and S. altissima has subsp. altissima and subsp. gilvocanescens. Some authors treat them all as four varieties of the single species S. canadensis. They will always be a challenge to readily separate. While multiple other references all have their two cents worth, our descriptions are based closely on those found in Flora of North America and based on our own field observations over time.

Plants with involucres (the set of bracts surrounding the base of flowerhead) 2 to 3 mm long are either S. canadensis or S. altissima susp. gilvocanescens, where S. altissima subsp. altissima has involucres 3 to 4.5+ mm long. Numbers of involucres on mature plants should be measured to obtain a reasonable average. Plants with hairs on the lower leaf surface as well as the veins are either S. altissima or S. canadensis var. hargeri. Beyond that, S. altissima has longer pappus hairs and thicker, firmer leaves that are minutely toothed or mostly toothed in the tip half where S. canadensis leaves are thinner, more lax, mostly toothed nearly to the leaf base, and is generally less hairy throughout. S. canadensis also never has stem galls where S. altissima frequently does.

• S. canadensis subsp. canadensis stems are hairless to sparsely hairy below mid-stem, and leaf undersides are hairless or hairy only along major veins. Involucre 2 to 3 mm (max 1/8 inch) long, pappus hairs less than 2.3 mm long.
• S. canadensis subsp. hargeri stems are sparsely to moderately hairy below mid-stem and leaf undersides are hairy along veins as well as minutely hairy on the surface. It also has a distinctive graceful, cascading panicle that is wider than long. Involucre 2 to 3 mm long, pappus hairs less than 2.3 mm long.
• S. altissima var. altissima stems are moderately hairy to the base, though hairs may wear off later in the season, leaf undersides are moderately hairy on the surface and more densely so on the veins. Involucre 3 to 4.5+ mm long, pappus hairs more than 2.4 mm long.
• S. altissima var. gilvocanescens stems are moderately hairy to the base, though hairs may wear off later in the season, leaf undersides are moderately hairy on the surface and more densely so on the veins. Involucre 2 to 3 mm long, pappus hairs more than 2.4 mm long.

The third species in this complex, Giant Goldenrod (S. gigantea), has stems hairless below the flower clusters that often have a waxy coating, its leaves are toothy and hairless except sometimes on the veins, and it also frequently has galls on the lower stem. Contrary to popular belief, Canada Goldenrod tends to be far less frequent and is less aggressive than Tall Goldenrod and typically occurs in moister sites, often in or near wetlands. We have only encountered var. canadensis from Kanabec County north and seems to be most common up into the Arrowhead.

Do take the county distribution map with a very large grain of salt—many of the herbarium records for S. canadensis are from a time when it and S. altissima were considered a single species and someone (a glutton for punishment, no doubt) still needs to review all the actual specimens and separate them out, if they can, then update the DNR's MNTaxa county distributions.

Canada Goldenrod is one of several North American Goldenrod species that have been introduced in Europe and become invasive there. We need to stop moving everything around the planet, really we do.