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Published In: Genera et Species Asterearum 9–10, 135–136. 1832. (Jul-Dec 1832) (Gen. Sp. Aster.) Name publication detail
 

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26. Symphyotrichum Nees (aster)

Plants perennial or rarely annual herbs, usually with short and stout rhizomes (elongate in a few species), less commonly with a short, woody rootstock, rarely taprooted. Stems 1 to few, erect or ascending, unbranched or branched, with fine or less commonly coarse, longitudinal lines or ribs, glabrous or variously hairy. Basal leaves present or absent at flowering. Stem leaves usually gradually reduced toward the tip, variously shaped, glabrous or hairy. Inflorescences usually relatively elongate (occasionally short and broad in poorly developed or young plants), not appearing flat-topped or hemispherical, the branches sometimes appearing racemose, the heads short- to long-stalked, the bracts often (but not always) relatively numerous and conspicuously more slender than the leaves. Heads radiate (appearing discoid in S. ciliatum), not sticky or resinous. Involucre 3–10 mm long, cup-shaped to obconical or slightly bell-shaped. Involucral bracts in 3–9 subequal or unequal, overlapping series, 0.2–0.8 mm wide (to 1.2 mm in S. turbinellum) and mostly 4–10 times as long as wide, linear to narrowly lanceolate or narrowly oblanceolate, the tip ascending or less commonly spreading to reflexed, with a usually white to pale straw-colored, relatively thin base having a very slender, green midvein, this broadened to an ovate to broadly diamond-shaped green portion toward the tip, sometimes also with narrow purple margins. Receptacle flat or shallowly convex, often with minute, irregular ridges around the concave attachment points of the florets. Ray florets 6–75(–100) (or appearing absent in S. ciliatum, in which the marginal pistillate florets have inconspicuous, tubular corollas shorter than the pappus and disc corollas), pistillate, the corolla white, pink, lavender to purple, or purplish blue. Disc florets 6–100, perfect, the corolla shallowly to relatively deeply lobed, yellow, usually turning reddish purple to brownish purple after the pollen has been shed, not persistent at fruiting. Pappus of the ray and disc florets similar (the outermost bristles sometimes appearing slightly shorter), of 1(2) series of numerous (mostly 60–90) finely barbed bristles, these all tapered toward the tip, white to grayish white, straw-colored, light tan, or pale orangish brown. Style branches with the sterile tip (beyond the stigmatic lines) (0.2–)0.3–0.5 mm long, linear to lanceolate. Fruits narrowly obovoid, often somewhat flattened, with 2–6 ribs, glabrous or sparsely hairy, variously tan or brown. About 90 species, North America to South America.

Symphyotrichum is the largest segregate of Aster in the New World and includes most of the Missouri species formerly placed in that genus. It is less closely related to the Old World species of true asters (see the treatment of Aster for further discussion) than it is to the American Eurybia and the group of genera related to Machaeranthera Nees (Semple et al., 2002). Generic limits and relationships are still somewhat unsettled within this group. Symphyotrichum is morphologically variable, and the classification and taxonomic relationships within some groups of closely related taxa also remain controversial.

The change in disc corolla color from yellow to reddish purple in most species of Symphyotrichum and in a few related genera of tribe Astereae has been remarked upon by many botanists. Niesenbaum et al. (1999) investigated this color change in S. racemosum (as Aster vimineus) and determined that the development of reddish pigmentation in disc corollas was correlated with a reduction in the quantity of pollen available in a given floret, but it apparently resulted in increased overall visitation of heads by insects that are potential pollinators.

Steyermark (1963) noted that several asters provide browse for deer (especially the basal rosettes during the winter months) and that the fertile portions are eaten by turkeys and other wildlife. A number of species of Symphyotrichum are cultivated as garden ornamentals in the United States and Canada. Some of the species with larger heads and purple rays are choice ornamentals for the garden. However, care should be taken in planting the species with smaller heads and white ray corollas, as most of these can spread aggressively both by fruits and rhizomes. For situations where large displays of white-rayed heads are desired, species and cultivars of Boltonia appear to be a more easily managed choice.

 

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1 1. Basal and lower stem leaves long-petiolate (the petiole sometimes winged) and the blade with a cordate to abruptly rounded or less commonly truncate base

2 2. Involucral bracts with the tips spreading to reflexed; ray florets (18–)20–45 ... 1. S. ANOMALUM

Symphyotrichum anomalum
3 2. Involucral bracts with the tips appressed or strongly ascending; ray florets 10–25

4 3. Leaf blades with the margins entire or rarely with a few minute, widely spaced teeth, at least the upper surface strongly roughened (sandpapery); involucral bracts all or mostly with the midvein fairly abruptly expanded into a broadly diamond-shaped (up to 2.5 times as long as wide) green area toward the tip ... 14. S. OOLENTANGIENSE

Symphyotrichum oolentangiense
5 3. Leaf blades (at least those of the lower leaves) with the margins more densely or deeply toothed, the upper surface glabrous or hairy but at most only somewhat roughened, the undersurface with relatively soft hairs; involucral bracts with the midvein gradually expanded into a narrowly diamond-shaped or narrowly elliptic (2.5–5.0 times as long as wide) green area toward the tip (species difficult to distinguish)

6 4. Involucral bracts relatively short-tapered or narrowed at the tip, bluntly to sharply pointed or with an abrupt, short, sharp point, the midvein expanded into a well-defined, diamond-shaped or elliptic (mostly 3–5 times as long as wide), green area toward the tip; basal and lower stem leaves with the petiole unwinged or less commonly very narrowly winged ... 3. S. CORDIFOLIUM

Symphyotrichum cordifolium
7 4. Involucral bracts relatively long-tapered at the tip, sharply pointed, the midvein slightly expanded into a sometimes indistinct, narrowly elliptic to nearly linear (mostly 6–10 times as long as wide) green area toward the tip; some or all of the basal and lower stem leaves with the petiole noticeably winged

8 5. Stems moderately to densely and evenly hairy, at least above the midpoint; ray florets with the corollas usually purplish blue (sometimes pale), less commonly lavender ... 4. S. DRUMMONDII

Symphyotrichum drummondii
9 5. Stems glabrous or sparsely to moderately hairy in longitudinal lines or bands toward the tip; ray florets with the corollas usually white, less commonly pale lavender ... 24. S. UROPHYLLUM

Symphyotrichum urophyllum
10 1. Basal and lower stem leaves not with both character states as above, either sessile to short-petiolate or with the blade gradually rounded to tapered at the base

11 6. Heads appearing discoid, the pistillate marginal florets with the inconspicuous, tubular corolla shorter than the pappus and disc corollas ... 2. S. CILIATUM

Symphyotrichum ciliatum
12 6. Heads radiate, the pistillate marginal florets with the well-developed ligulate corolla noticeably longer than the pappus and the disc corollas

13 7. Leaves with both surfaces densely pubescent with appressed, silky hairs, appearing grayish or silvery ... 21. S. SERICEUM

Symphyotrichum sericeum
14 7. Leaves glabrous or more commonly with 1 or both surfaces sparsely to moderately pubescent, the hairs not appressed and silky, the leaves not appearing grayish or silvery

15 8. Heads with the stalk and involucre with short, gland-tipped hairs, the upper portions of the stem and the leaves sometimes also glandular

16 9. Involucral bracts mostly linear, long-tapered to the slender, sharply pointed tip; ray florets 40–100; stem leaves with the base cordate, clasping the stem ... 11. S. NOVAE-ANGLIAE

Symphyotrichum novae-angliae
17 9. Involucral bracts mostly narrowly oblong to narrowly oblong-oblanceolate, all but the inner series angled or short-tapered to the sharply pointed tip; ray florets 12–35; stem leaves with the base variously shaped

18 10. Stem leaves narrowed or rounded at the sometimes slightly expanded base, occasionally appearing truncate, but not or only slightly clasping the stem; involucral bracts subequal to somewhat unequal, the tips all spreading to recurved ... 12. S. OBLONGIFOLIUM

Symphyotrichum oblongifolium
19 10. Stem leaves deeply cordate at the base, strongly clasping the stem; involucral bracts strongly unequal, the tips erect to somewhat loosely ascending, some of them occasionally somewhat spreading ... 16. S. PATENS

Symphyotrichum patens
20 8. Heads with the stalk and involucre glabrous to variously hairy, but not glandular; stems and leaves not glandular

21 11. Leaves (except the basal and sometimes the lowermost stem leaves) with the relatively broad base strongly clasping the stem, often deeply cordate

22 12. Stems moderately to densely and evenly hairy ... 16. S. PATENS

Symphyotrichum patens
23 12. Stems glabrous below the inflorescence or inconspicuously and sparsely hairy in longitudinal lines toward the tip and occasionally immediately below the upper leaf bases

24 13. Involucral bracts subequal or somewhat unequal but not in several well-defined series, often relatively long-tapered at the tip, the midvein expanded below the midpoint into a narrowly elliptic, green apical area; leaves not glaucous ... 19. S. PUNICEUM

Symphyotrichum puniceum
25 13. Involucral bracts unequal in several well-defined series, angled or relatively short-tapered at the tip, the midvein expanded near the tip into a diamond-shaped or broadly elliptic, green apical area; leaves glabrous and usually glaucous ... 8. S. LAEVE

Symphyotrichum laeve
26 11. Leaves with the base slender or slightly expanded, sometimes somewhat sheathing but not or only slightly clasping the stem, tapered, angled, rounded, or occasionally appearing truncate

27 14. All or at least the outermost few series of involucral bracts somewhat inrolled toward the tip, tapered to a somewhat thickened, awl-shaped (outward curved then upward curved), sharply pointed, green tip, with a short, white to yellowish- or purplish-tinged, relatively stout and spinelike or less commonly slender and hairlike point at the very tip

28 15. Plants annual, taprooted; involucral bracts entire and glabrous along the margins ... 22. S. SUBULATUM

Symphyotrichum subulatum
29 15. Plants perennial, the rootstock relatively short and stout, fibrous-rooted, sometimes also with rhizomes; involucral bracts minutely toothed or irregular and often sparsely short-hairy along the margins

30 16. Involucre 3.0–4.5 mm long, narrowly ellipsoidal to narrowly cup-shaped or nearly cylindrical when fresh (becoming obconical when pressed); disc florets 6–12; ray florets 10–16(–18), the corollas 3.5–6.0 mm long ... 15. S. PARVICEPS

Symphyotrichum parviceps
31 16. Involucre 4–8 mm long, urn-shaped to more or less cup-shaped when fresh (becoming bell-shaped to broadly obconical when pressed); disc florets 20–40; ray florets 15–35, the corollas 5–10 mm long ... 17. S. PILOSUM

Symphyotrichum pilosum
32 14. Involucral bracts not inrolled toward the tip, angled or tapered to a relatively flat, sharply pointed tip, this sometimes with a minute, white to tan or purplish-tinged, slender (occasionally hairlike) point at the very tip

33 17. Involucre (6–)7–12 mm long, the bracts in 6–9 unequal series, rounded or angled to a bluntly pointed or sometimes sharply pointed tip; ray florets with the corolla 10–18 mm long, purple to purplish blue ... 23. S. TURBINELLUM

Symphyotrichum turbinellum
34 17. Involucre 2.5–7.0(–8.0) mm long, the bracts in 3–6 subequal to unequal series, angled or tapered to a sharply pointed tip; ray florets with the corolla 2.5–10.0(–12.0) mm long, usually white when fresh, rarely pinkish-tinged or lavender (often drying purplish or blue)

35 18. Plants taprooted annuals; stems and leaves glabrous ... 22. S. SUBULATUM

Symphyotrichum subulatum
36 18. Plants fibrous-rooted perennials, the rootstock usually stout and somewhat woody, often also with rhizomes; stems and/or leaves sparsely to moderately hairy (check closely with magnification, as the hairs may be inconspicuous and in lines or only along leaf midveins)

37 19. At least the outer involucral bracts loosely ascending to spreading, sparsely to moderately hairy on the outer surface (sometimes only along the midvein), relatively densely hairy along the margins, the tip with a minute, bristlelike extension of the midvein or a short, hard, white to yellowish or purple, spinelike point

38 20. Involucre 3–5 mm long; ray florets 8–20; heads relatively numerous along the inflorescence branches, all or mostly oriented toward 1 side of each branch ... 6. S. ERICOIDES

Symphyotrichum ericoides
39 20. Involucre 5–8 mm long; ray florets (15–)20–35; heads appearing fewer, solitary or in small clusters at the tips of the inflorescence branches, oriented in various directions ... 7. S. FALCATUM

Symphyotrichum falcatum
40 19. Involucral bracts erect or strongly ascending, the outermost occasionally somewhat loosely ascending, glabrous or sparsely hairy on the outer surface, glabrous (but often somewhat uneven) or sparsely hairy along the margins, the tip bluntly to sharply pointed, lacking a bristlelike extension of the midvein or a short, hard, spinelike point (or, if sometimes with a short, bristlelike tip, in S. ontarione, then the body of the bract flat and not inrolled toward the tip)

41 21. Disc corollas with the lobes relatively long (0.9–1.7 mm), 45–75 percent of the total length of the expanded upper portion (above the slender basal portion of the tube) of the corolla

42 22. Stem leaves with the undersurface moderately to densely short-hairy along the midvein and rarely with a few hairs along the lateral veins, otherwise glabrous (except for the minutely hairy margins) ... 10. S. LATERIFLORUM

Symphyotrichum lateriflorum
43 22. Stem leaves (at least the median and upper ones) with the undersurface sparsely to moderately and evenly short-hairy on the undersurface (including the tissue between the veins), sometimes with slightly longer or denser hairs along the midvein ... 13. S. ONTARIONE

Symphyotrichum ontarionis
44 21. Disc corollas with the lobes relatively short (0.4–1.2 mm), 15–45 percent of the total length of the expanded upper portion (above the slender basal portion of the tube) of the corolla

45 23. Leaf undersurface with the veinlets relatively prominent, forming a network with areoles that are about as long as wide or slightly longer than wide (these often containing free veinlets); ray corollas purple or bluish purple ... 18. S. PRAEALTUM

Symphyotrichum praealtum
46 23. Leaf undersurface with the secondary veins and/or veinlets either faint or, if relatively prominent, then forming a network with areoles that are much longer than wide (these sometimes containing free veinlets); ray corollas mostly white when fresh (often turning somewhat bluish-tinged when dried), less commonly bluish-tinged or lavender (species difficult to distinguish)

47 24. Involucre 3.5–8.0 mm long; rays 5–12 mm long; heads solitary or clustered at the branch tips or oriented in various directions and more or less racemose along the inflorescence branches; largest stem leaves (3–)6–40 mm wide ... 9. S. LANCEOLATUM

Symphyotrichum lanceolatum
48 24. Involucre 2.5–4.0 mm long; rays 3–8 mm long; heads solitary at the branch tips or arranged in mostly 1-sided racemes along the inflorescence branches; largest stem leaves 1–7(–11) mm wide

49 25. Median and inner series of involucral bracts with a relatively short, elliptic to diamond-shaped green tip, this up to 1/2 the length of the bract; heads mostly appearing solitary at the ends of inflorescence branches or, if appearing racemose, then the heads mostly relatively long-stalked ... 5. S. DUMOSUM

Symphyotrichum dumosum
50 25. Median and inner series of involucral bracts with a relatively elongate, elliptic green tip, this mostly more than 1/2 the length of the bract; heads appearing solitary or in clusters at the ends of inflorescence branches or, if appearing racemose, then the heads mostly relatively short-stalked

51 26. Heads mostly in small clusters toward the branch tips or appearing racemose, the stalks relatively short and few-bracted ... 9. S. LANCEOLATUM

Symphyotrichum lanceolatum
52 26. Heads mostly solitary at the branch tips or sometimes in small, loose clusters, the stalks mostly relatively long and many-bracted ... 20. S. RACEMOSUM Symphyotrichum racemosum
 
 
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