Solidago L.
Family: Asteraceae
Solidago image
Emmet J. Judziewicz  

Key to Wisconsin Solidago

    • 1a.Heads in small clusters at the tip of inflorescence branches in a terminal corymbiform (flat-topped or low dome-like) inflorescence 2

    • 1b.Heads spread along inflorescence branches in a terminal pyramidal (rarely thyrsiform) panicle, or in clusters or short racemes in the axils of upper leaves 5

    • 2a.Rays 10--20, white, more than 7 mm long; leaves linear to narrowly obovate; pappus hairs slightly wider near tip S. ptarmicoides

    • 2b.Rays 6--13, yellow, less than 6 mm long; leaves ovate to elliptic or linear-lanceolate; pappus hairs slender to the tip 3

    • 3a.Blades of cauline leaves broadly ovate to elliptic, densely hispid to strigose on both surfaces; stems densely pubescent S. rigida

    • 3b.Blades of cauline leaves narrowly elliptic to linear-lanceolate, glabrous, the margin scabrous, upper cauline leaves widest at or below the middle; stems glabrous or nearly so 4

    • 4a.Inflorescence branches and pedicels densely short-hispid; cauline leaves often folded lengthwise, curved downward, acute, entire, slightly triple-nerved S. riddellii

    • 4b.Inflorescence branches and pedicels glabrous; cauline leaves flat, obtuse, often obscurely serrate, not triple-nerved S. ohioensis

    • 5a.Basal and lower cauline leaves usually present at flowering time, their petioles clasping (encircling) more than half the circumference of the stem 6

    • 5b.Basal and lower cauline leaves lacking at flowering time, or, if present, their petioles not widened and clasping the stem 7

    • 6a.Leaves thick and fleshy, margins entire; heads secund, borne on long pedicels on the upper side of horizontal inflorescence branches S. sempervirens

    • 6b.Leaves not notably thick, margins shallowly serrate or entire; heads rarely secund, the inflorescence usually narrow or thyrsifom with lower branches short or ascending S. uliginosa

    • 7a.Inflorescence a terminal pyramidal panicle, usually nodding at the tip, the longer branches spreading or curved downward, with heads secund (most borne on the upper side of the branches and oriented upward), rarely a thyrsiform panicle with ascending lower branches 8

    • 7b.Inflorescence of axillary clusters or a terminal panicle not nodding at the tip, with lower branches not curved downward, the branches not one-sided, heads oriented in several directions on all sides of the branches, not secund 19

    • 8a.Cauline leaves triple-nerved, with a pair of prominent lower lateral veins prolonged parallel to the midrib and more conspicuous than the other veins 9

    • 8b.Cauline leaves pinnately-veined, the lower lateral veins not prolonged parallel to the midrib, or with one or two pairs of lateral veins somewhat prolonged, but not prominent 14

    • 9a.Stems glabrous below the inflorescence 10

    • 9b.Stems pubescent below the inflorescence, at least on the upper half 12

    • 10a.Inflorescence branches and pedicels densely pubescent; basal leaves absent, lower cauline leaves withered or absent by flowering time; mid and upper cauline leaves numerous, overlapping on pressed specimens; abaxial leaf surface glabrous or with hairs on the veins; stems usually glaucous S. gigantea

    • 10b.Inflorescence branches and pedicels glabrous; basal and lower cauline leaves linear to oblanceolate with long petioles; mid and upper cauline leaves few, narrow, glabrous, often with fascicles of small linear leaves in the axils; stems not glaucous. 11

    • 11a.Basal and lower cauline leaves usually 2--8 cm wide; plants with a stout caudex; achenes hairy S. juncea

    • 11b.Basal and lower cauline leaves usually less than 2 cm wide; plants with a slender rhizome; achenes glabrous to sparsely strigose S. missouriensis

    • 12a.Leaves densely canescent on both sides, ovate to broadly elliptic, 2—5 times as long as wide; ray florets 3--8 per head S. mollis

    • 12b.Leaves scabrous, puberulent, or nearly glabrous on the adaxial side, mostly lanceolate, or narrowly elliptic, more than 5 times as long as wide; ray florets usually more than 8 13

    • 13a.Involucre less than 3 mm high; heads with 6--12 ray florets; disk florets usually 3, less than 3 mm high; most cauline leaves relatively thin and sharply serrate; main branches of well-developed inflorescences typically slender and wide spreading; shorter plants forming smaller clones S. canadensis

    • 13b.Involucre 3--5 mm high; heads with 10--22 ray florets; disk florets usually more than 3, more than 3 mm high; upper cauline leaves leaves moderately firm and thick, usually subentire; main branches of well-developed inflorescences relatively stout and ascending; usually tall plants with long rhizomes, forming large clones S. altissima

    • 14a.Stems pubescent most of their length 15

    • 14b.Stems glabrous or slightly pubescent at the base of the inflorescence 16

    • 15a.Stem and leaves grayish, densely puberulent with minute hairs; basal and lower cauline leaves oblanceolate, much larger than the mid-cauline leaves; leaf margins entire to crenate S. nemoralis

    • 15b.Stem and leaves hirsute with hairs about 0.5 mm long; cauline leaves similar, elliptic-lanceolate; margins sharply serrate S. rugosa

    • 16a.Mid-cauline leaves adaxially scabrous or hirsute, broadly elliptic, much larger than the small rhombic leaves and bracts in the inflorescence 17

    • 16b.Mid-cauline leaves glabrous, linear-lanceolate, grading into small linear leaves in the inflorescence 18

    • 17a.Adaxial surface of leaves strongly scabrous; stem angular with raised ridges S. patula

    • 17b.Both leaf surfaces sparsely hirsute; stem smooth and terete S. ulmifolia

    • 18a.Basal and lower cauline leaves usually 2--8 cm wide; plants with a stout caudex; achenes pubescent S. juncea

    • 19a.Basal and lower cauline leaves smaller than upper leaves, or withered by flowering time; inflorescence of clusters or short racemes in the axils of cauline leaves, all but the uppermost clusters shorter than the subtending leaves 20

    • 19b.Basal and lower cauline leaves persisting and larger than the upper leaves; mid-stem leaves usually entire or crenate, and not subtending inflorescences 21

    • 20a.Mid-stem leaf blades broadly ovate, abruptly contracted to a winged petiole; stem sparsely pubescent, angled and zig-zagging node to node S. flexicaulis

    • 20b.Leaf blades lanceolate, sessile; stem straight, glabrous, glaucous, and terete S. caesia

    • 21a.Stems sparsely to densely pubescent from base through inflorescence; leaves pubescent on both sides 22

    • 21b.Stems glabrous below the middle; leaves glabrous or nearly so 23

    • 22a.Ray flowers yellow when fresh; involucres 4--7 mm long, the narrow phyllaries greenish to base and margin S. hispida

    • 22b.Ray flowers white when fresh; involucres 3--4.5 mm long; the wide phyllaries pale green at the tip, whitish at base and margin S. bicolor

    • 23a.Basal and lower cauline leaves 6--18 times as long as wide, tapering to long clasping petioles S. uliginosa

    • 23b.Basal and lower cauline leaves usually less than 6 times as long as wide; petioles not clasping stem; plants usually growing in dry habitats 24

    • 24a.Achenes glabrous; mid cauline leaves firm, most narrowly elliptic, margins entire to sparsely serrulate S. speciosa

    • 24b.Achenes hairy; mid-cauline leaves lanceolate to broadly elliptic or oblanceolate, serrate 25

    • 25a.Heads and leaves viscid-resinous when fresh; mid-cauline leaves tapering to winged petioles; many pedicels 5--15 mm long S. simplex

    • 25b.Heads not viscid; mid-cauline leaves tapered to a sessile base; most pedicels less than 5 mm long S. sciaphila

Goldenrods are familiar late summer and autumn wildflowers easily recognized by the large inflorescences of many small golden-yellow heads. The identification of species, however, is often difficult. Most of the common wide-ranging species are highly variable. Many of the features used in keys can be altered by habitat, herbivore damage to the stem apex, hybridization, and other factors. Identification is often easier in the field where traits such as the presence of basal leaves and rhizomes, height of undamaged stems, size of clone, etc. can be observed for the whole population and "typical" characters determined. This genus of more than 100 species, all but one native to North America, has been trimmed in some treatments by the removal of the species with flat-topped (corymbiform) inflorescences. Recent studies support the transfer of the "grass-leaved goldenrods" to Euthamia, but the species sometimes placed in Oligoneuron (included in this key in the first part of couplet one) fit well in Solidago.