Leaves: basal withering by flowering, proximalmost cauline sessile, withering by flowering, not as large as proximal and sometimes distal, 3-nerved (two lateral nerves prominent, sometimes obscurely so and only on proximal leaves). Heads in thyrsiform-paniculiform, usually congested cone-shaped (pyramidal), secund, sometimes leafy arrays (club-shaped in S. elongata), proximal branches often arching, secund, branches sometimes shorter than subtending leaves. Phyllaries not striate, sometimes stipitate-glandular. Pappus bristles usually in 2 series (sometimes similar, inner usually weakly, if at all clavate, rarely moderately so).

Distribution

North America, South America, introduced in Eurasia.

Discussion

Species ca. 16 (11 in the flora).

Subsection Triplinerviae includes the Solidago canadensis complex, which fully deserves its reputation for being one of the more taxonomically challenging species assemblages in North America. All members have ± 3-nerved mid cauline leaves, although the trait is obscure in the narrow-leaved S. altiplanities, S. juliae, and S. tortifolia, and can be obscure in the broader-leaved S. lepida and S. shortii. As evidenced by the many combinations under most names, opinions on how to treat the complex have been numerous, some of them due to misapplication of the basionyms. A. Cronquist (1994 and earlier) placed many of the species in S. canadensis itself, separating out only the more glabrous taxa, but inconsistently not all of them. The admittedly radical classification followed below developed from work done to prepare this treatment. Stem pubescence (kind and distribution of hairs), glandularity, leaf features (width, serrations), and array features are emphasized in distinguishing species. The geographic distribution of diploid members of the complex were also critical in assessing which races belonged in which species. It is possible that at one point during glacial times, each of the diploid races was geographically isolated. Subsequent formation of tetraploid and hexaploid races from most of those resulted in range expansions into the territories of other races, allowing hybridization to occur, especially between polyploids. The result is what occurs today: a series of mostly geographically distinct diploids with overlapping polyploid ranges forming an apparent classic pillar complex. Either convergence or hybridization may be responsible for the current overlap in the ranges of morphologic traits that are relatively distinct at the diploid level.

Selected References

None.

Lower Taxa

Solidago altiplanities, Solidago altissima, Solidago canadensis, Solidago elongata, Solidago gigantea, Solidago juliae, Solidago leavenworthii, Solidago lepida, Solidago rupestris, Solidago shortii, Solidago tortifolia

Key

1	Rays mostly 2–8; mid cauline leaves lanceolate or linear and sometimes twisted	> 2
1	Rays mostly 8–15; mid cauline leaves lanceolate to oblanceolate, or if linear then not twisted	> 5
2	Mid cauline leaves linear (largest 2–7(–10) mm wide), sometimes twisted	> 3
2	Mid cauline leaves lanceolate, never twisted; Appalachian plateau	> 4
3	Array branches ascending or ascending and distally recurved; mid cauline leaves to 90 mm, not twisted; canyons, escarpments, gypsum outcrops, Red River Valley, Oklahoma and Texas	Solidago altiplanities
3	Array branches spreading, recurved; leaves 50 mm or less, often twisted; outer coastal plain, North Carolina to Texas	Solidago tortifolia
4	Involucres 2–3 mm; rays 1–2 mm	Solidago rupestris
4	Involucres 4–5 mm; rays 2–3 mm; Kentucky	Solidago shortii
5	Stems glabrous, usually glaucous; array leaves, peduncle bracts, and phyllaries not mi-nutely stipitate-glandular (moister soils, e forests onto prairies)	Solidago gigantea
5	Stems strigillose or short-villous, at least in arrays to partway down stems, or array leaves, peduncle bracts, or phyllaries minutely stipitate-glandular	> 6
6	Leaves moderately to densely villous or strigillose, sometimes more so on abaxial nerves	> 7
6	Leaves glabrous or sparsely villoso-strigillose, more so abaxially than adaxially, especially along main nerves	> 9
7	Mid to distal cauline leaves evidently serrate; arrays broadly pyramidal; seCanada, New York to n Virginia, w to Minnesota and Iowa	Solidago canadensis
7	Mid to distal cauline leaves minutely serrate to entire; arrays elongate-pyramidal to broadly so	> 8
8	Stems villoso-strigillose, sometimes sparsely so proximally; leaf faces short scabroso-strigillose adaxially, more densely strigilloso-villous abaxially, more so along abaxial nerves; arrays narrowly to broadly pyramidal; e Canada and United States, w across Great Plains to mountains	Solidago altissima
8	Stems densely and closely villoso-tomentose; leaf faces densely and evenly villoso-strigillose; arrays 2–3 times as long as wide; Edwards Plateau andtrans-Pecos Texas	Solidago juliae
9	Distalmost leaves, peduncle bracts, and/or phyllaries sparsely to moderately minutely stipitate-glandular; arrays usually leafy, club-shaped (sometimes pyramidal, secund, not leafy, in Rocky Mountains from British Columbia south, var. salebrosa); distal leaves more than 10 mm wide, sometimes largely, coarsely serrate; Alaska to Arizona and New Mexico in mountains, across Canada to New Brunswick and Newfoundland	Solidago lepida
9	Distalmost leaves, peduncle bracts, and phyllaries not minutely glandular; arrays not leafy, narrowly to broadly secund pyramidal or club-shaped, much longer than broad (rarely leafy proximally); distal leaves usually less than 10 mm wide, finely serrate	> 10
10	Arrays club-shaped (2–3(–5) times as long as wide); California, Oregon, Washington	Solidago elongata
10	Arrays secund, pyramidal; e North America	> 11
11	Mid to distal cauline leaves evidently serrate or serrulate, teeth 3–10, largest (1.5–)2–4 mm, adaxial faces sparsely scabrous, abaxial faces puberulent along and between nerves; Newfoundland to Minnesota, s to Iowa and Virginia	Solidago canadensis
11	Mid to distal cauline leaves serrulate, teeth 1–10, fine, largest 0.25–0.5 mm, faces glabrous or with short hairs in lines along 3 nerves; Alabama, Florida, Georgia, North Carolina, South Carolina	Solidago leavenworthii