4. Solidago caesia L. (blue-stemmed goldenrod, wreath goldenrod)

Pl. 239 c–e; Map 993

Plants with the rootstock short, stout, and sometimes branched, sometimes also producing long, slender rhizomes. Stems 1 to several, 30–100 cm long, erect to more commonly arched or pendant, sometimes with fine, inconspicuous, longitudinal lines but not noticeably ridged or grooved, glabrous, not shiny, glaucous. Leaves chiefly cauline, the largest leaves in the lower 1/3 of the stem, the basal and lower stem leaves absent at flowering. Basal and lowermost stem leaves with the blade 6–10 cm long, 1–3 cm wide, mostly 3–8 times as long as wide, narrowly elliptic-oblanceolate to elliptic or elliptic-obovate, relatively thin, tapered to a sessile base, tapered to a sharply pointed tip, the margins sharply toothed and usually inconspicuously hairy, the surfaces glabrous, the undersurface with 1 main vein, the fine, pinnate secondary veins usually relatively easily observed (these usually forming an irregular network). Median and upper stem leaves 2–8 cm long, elliptic-oblanceolate to narrowly elliptic, the margins of the uppermost leaves sometimes entire, otherwise similar to the lower stem leaves. Inflorescences of axillary clusters, the heads oriented in several directions. Involucre 2.5–4.5 mm long, the bracts in 3–5 unequal series. Involucral bracts mostly oblong to narrowly oblong and rounded to bluntly pointed (those of the outer series often oblong-lanceolate and sharply pointed) at the appressed-ascending tip, the thin, white to yellowish white margins hairy toward the tip, the outer surface glabrous, with a poorly defined, green central region toward the tip, this tapered abruptly to the midvein above or below the bract midpoint, the midvein often slightly thickened and sometimes with a faint, additional pair of veins present. Receptacle naked. Ray florets (1–)2–5, the corollas 3.0–3.5 mm long, yellow. Disc florets 5–9, the corollas 3.0–3.5 mm long, the lobes 0.9–1.5 mm long, yellow. Pappus 2.5–3.0 mm long, a few of the bristles often slightly thickened toward the tip. Fruits 1.0–1.8 mm long, narrowly ellipsoid-obovoid, finely hairy. 2n=18. August–October.

Scattered in the southern quarter of the state, almost entirely within the Ozark Division (eastern U.S. west to Wisconsin and Texas; Canada). Bases and ledges of shaded bluffs, banks of streams and rivers, bottomland forests, and mesic upland forests; also roadsides.

This species is found most frequently along sheltered bluffs and adjacent lower terraces of streams. It does well in full sun or partial shade in the wildflower garden with its graceful, arching, glaucous stems and attractive clusters of heads.

Cook and Semple (2004) recently divided the species into two varieties, based mainly on differences in leaf morphology. They segregated plants with broadly lanceolate to elliptic or elliptic-ovate median leaves 5–9 cm long and less-arched stems as var. zedia R.E. Cook & Semple, which they stated to occur from southern Arkansas through Mississippi into northern Florida. They characterized the var. caesia as having narrowly lanceolate midstem leaves 5–15 cm long and strongly arched stems. Although Cook and Semple did not include Missouri in the range of var. zedia, Rachel Cook annotated about a third of the specimens from throughout the species range in the state as this variety. The determinations of these specimens seem equivocal, with a number of the Missouri specimens seemingly intermediate in leaf shape. None of the specimens in question include observations by the collectors on stem arching. In light of the difficulties in applying the defining features of these infraspecific taxa to plants in the Missouri flora, it seems wisest for the present time not to attempt a formal recognition of varieties.