9. Symphyotrichum lanceolatum (Willd.) G.L. Nesom (tall white aster, panicled aster)

Aster lanceolatus Willd.

A. simplex Willd.

Pl. 246 e, f; Map 1021

Plants perennial herbs, often somewhat colonial from relatively long, slender, branched rhizomes. Stems usually solitary, 20–150 cm long, unbranched or with few to most commonly many spreading to ascending branches mostly above the midpoint, sparsely to moderately pubescent with short, spreading or curled hairs toward the tip, these usually in longitudinal lines or bands, usually glabrous toward the base or sometimes nearly throughout. Basal and/or lower stem leaves usually absent from the flowering stems, sessile or with a short, poorly differentiated petiole, the blade 1–8 cm long, 0.5–2.0 cm wide, oblanceolate, tapered at the base, rounded or angled to a bluntly or sharply pointed tip, the margins with spreading to forward-pointing hairs and usually toothed or scalloped, the surfaces usually glabrous, the secondary veins on the leaf undersurface often difficult to distinguish from the veinlets, forming an irregular network of elongated areoles. Median and upper stem leaves progressively smaller or not much reduced beyond the median leaves, the larger ones occasionally withered by flowering time, sessile, the base sometimes slightly expanded but not clasping the stem, the blades 1–14 cm long, linear to narrowly elliptic or oblanceolate to broadly oblanceolate, the margins entire or sparsely toothed, angled or tapered at the base, angled or tapered to a sharply pointed tip, otherwise similar to the lower stem leaves. Inflorescences usually appearing as panicles with short to relatively long, loosely ascending to spreading branches (these racemose or more commonly with the heads solitary or in clusters toward the branch tips), the heads appearing mostly short-stalked and usually oriented in various directions, often relatively few per branch (except sometimes in var. interior), the bracts along the ultimate branches 0.2–1.0 cm long, relatively few, more or less leaflike, linear or narrowly oblong-lanceolate, somewhat shorter than the adjacent foliage leaves. Heads mostly 1.0–2.5 cm in diameter (including the extended ray corollas) at flowering. Involucre 3–7 mm long, cup-shaped to slightly bell-shaped when fresh (sometimes becoming obconical when pressed), the bracts in 3–5 more or less unequal, overlapping series. Involucral bracts linear-lanceolate to narrowly oblong-oblanceolate, angled or tapered at the usually sharply pointed tip, lacking a bristlelike or spinelike point at the ascending tip, the slender midvein broadened gradually in the apical 1/2–3/4 into a narrowly elliptic (4–10 times as long as wide), green tip, the outer surface glabrous or sparsely hairy, the margins often slightly irregular and sparsely hairy. Ray florets 20–45 in usually 1 or 2 series, the corollas well developed, 5–12 mm long, white (rarely pink, lavender, or bluish-tinged). Disc florets 15–40, the corollas 3–6 mm long, the slender portion of the tube noticeably shorter than the slightly expanded apical portion, the lobes 0.7–1.2 mm long, 30–45 percent of the total length of the expanded portion. Pappus bristles 3–6 mm long, white or off-white. Fruits 1.2–2.0 mm long, with 4 or 5 longitudinal ribs, gray to tan, moderately hairy, the hairs lacking swollen bases. 2n=32, 40, 48, 56, 64. August–October.

Scattered nearly throughout the state (U.S., Canada, Mexico). Bottomland forests, mesic upland forests, swamps, bases and ledges of bluffs, banks of streams, rivers, and spring branches, margins of ponds, lakes, and sinkhole ponds, fens, sloughs, and moist depressions in upland prairies; also pastures, fencerows, ditches, railroads, roadsides, and open, disturbed areas.

This is a widespread, variable species. It might be confused with S. lateriflorum and S. ontarione at one extreme and with S. racemosum at the other. These similarities led Semple and Brammall (1982) to hypothesize that S. ontarione might have evolved from past hybridization involving S. lanceolatum and S. lateriflorum. Putative hybrids have been recorded from Missouri with S. lateriflorum and S. praealtum.

Semple and Chmielewski (1987) were the latest to study the taxonomy of the S. lanceolatum polyploid complex (as Aster lanceolatus), arriving at a complex classification that included two subspecies, one of which was subdivided further into four varieties. Of these, the western ssp. hesperium (A. Gray) G.L. Nesom (A. hesperius A. Gray, A. lanceolatus ssp. hesperius (A. Gray) Semple & Chmiel.) was excluded from the Missouri flora by Steyermark (1963), who redetermined the sole historical Jackson County collection upon which earlier reports of this taxon in the state had been based. Barkley (1986), Yatskievych and Turner (1990), and Gleason and Cronquist (1991) have continued to include Missouri in the range of ssp. hesperium, but to date no specimens to confirm its presence in Missouri have come to light. It differs from ssp. lanceolatum in its subequal involucral bracts and somewhat larger, broader bracts subtending the heads. Of the four named variants within ssp. lanceolatum, all but the northern var. hirsuticaule (Semple & Chmiel.) G.L. Nesom (with densely and evenly hairy stems) have been reported from Missouri. The three varieties are not strongly marked in Missouri, except in their extremes, and some specimens are difficult to determine below the species level.