This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Perennial or rarely annual, mostly branching herbs, with alternate leaves, and corymbose or paniculate (rarely racemose or solitary) heads of both tubular and radiate flowers. Involucre hemispheric, campanulate or turbinate, its bracts various, imbricated in several series, the exterior ones usually smaller and shorter. Receptacle flat or convex, generally foveolate. Ray-flowers white, pink, purple, blue, or violet (very rarely yellowish), pistillate. Disk-flowers tubular, perfect, their corollas 5-lobed, usually yellow and changing to red, brown, or purple. Anthers obtuse and entire at the base. Style-branches flattened, their appendages subulate, lanceolate or ovate, acute. Pappus-bristles slender, numerous, scabrous or denticulate, usually in 1 series, sometimes in 2 series. Achenes mostly flattened and nerved. [Greek, star.]
A genus of not less than 250 species, most abundant in North America, where, in addition to the following, many others occur beyond our limits. A large number of the species apparently consist of many slightly differing races, and hybridism is also suspected. Known as Asters or Star-worts. Type species: Aster amellus L.
A. Basal and lower leaves, or some of them, cordate and slender-petioled. (See No. 50.)
1. None of the stem leaves cordate-clasping. * Rays white, violet, or rose.
§ Rays white, or rarely rose, usually 2-toothed; plants not glandular, † Involucre ovoid, campanulate or turbinate, its bracts mostly obtuse or rounded; basal leaves few and small, or commonly none (except in No. 5).
(a) Leaves membranous or thin, smooth, or nearly so. Heads short-peduncled, 9" broad or less, the disk turning crimson; leaves acute or short-acuminate.
1. A. carmesinus.
* Text prepared for our first edition with the assistance of Prof. Edward S. Burgess, here somewhat revised.
Heads long-peduncled, 9" broad or more, the disk turning brown or reddish brown; leaves long-acuminate. Heads 1' broad or more; leaves of the branches large, long, lanceolate, acuminate.
2. A. tenebrosus.
Heads 9"-12" broad; leaves of the branches small, obtuse, or acute.
3. A. divaricatus.
4. A. furcatus.
Heads 4"-5" high; inflorescence paniculate or glomerate.
Leaves acute, or short-acuminate, pilose beneath; inflorescence glomerate.
5. A. glomeratus.
Leaves long-acuminate, not pilose beneath; inflorescence open-paniculate.
6. A. Claytoni.
†† Involucre cylindric, its bracts tapering to an obtuse apex; basal leaves large, tufted. Bracts of the involucre pale, scarious, usually without herbaceous tips.
7. A. curvescens.
Bracts of the involucre broader, with herbaceous tips.
8. A. Schreberi.
§§ Rays violet, usually 3-toothed; plants glandular, † Predominant glands large, capitate; leaves thick, coarse, heavy. Sinus broad; glands chiefly confined to the inflorescence; plant usually harsh.
9. A. macrophyllus.
Sinus narrow; glands abundant on the leaves and stem; growing plant clammy.
10. A. roscidus.
†† Predominant glands minute, scarcely capitate; leaves usually thin.
(a) Inflorescence rather regular, flat, or convex-topped; plants usually less than 2 1/2° tall. Sinus broad, shallow.
Broader leaves orbicular-cordate, their teeth and the inflorescence-leaves inconspicuous.
11. A. ianthinus.
Broader leaves reniform, sharply incised; some inflorescence-leaves conspicuous.
12. A. violaris.
Sinus rather deep and narrow; broader leaves ovate-cordate, sharply serrate.
13. A. multiformis.
(.b) Inflorescence very irregular, paniculate-corymbose; plants often 4°-5° high; broader leaves large, cordate, acute.
14. A. nobilis.
** Rays blue or purple; plants not glandular, † Bracts of the involucre spreading or recurved; rays 30-45.
15. A. anomalus.
†† Bracts of the involucre appressed, or erect; rays 8-20. (a) Leaves all entire, or nearly so, thick, or firm.
Leaves nearly or quite glabrous above.
16. A. Shortii.
Leaves rough-puberulent on both sides, the upper bract-like.
17. A. azureus.
(b) Leaves nearly all sharply serrate, thin.
Heads 2"-3" high, numerous; bracts obtuse or obtusish.
Leaves rough; petioles not wing-margined; bracts appressed.
18. A. cordifolius.
Leaves smooth, or nearly so; petioles, or some of them, wing-margined.
19. A. Lowrieanus.
Heads 4 -5 high, usually few; bracts acute or acuminate.
20. A. Lindleyanus.
Heads 3"-5", high, numerous; bracts acute or acuminate. Stem densely and finely pubescent.
21. A. Drummondii.
Stem glabrous or nearly so; bract-tips spreading.
22. A. sagittifolius.
2. Stem leaves, or some of them, cordate-clasping; plant rough when dry.
23. A. undulatus.
B. No cordate and petioled leaves; those of the stem, or some of them, with more or less cordate or auricled clasping bases (only slightly auricled in A. tardiflorus, and sometimes in A. laevis).
1. Stem rough, or hirsute-pubescent.
* Leaves entire, oblong, linear, or lanceolate.
§ Heads 1'-2' broad; leaves sessile, strongly cordate-clasping.
† Stem rough; leaves oblong to lanceolate; involucre turbinate.
Leaves thick, firm, very rough, oblong to oval.
24. A. patens.
Leaves thin, roughish, oblong-lanceolate.
25. A. phlogifolius.
†† Stem hirsute; leaves lanceolate; involucre hemispheric; bracts viscid.
26. A. novae-angliae.
§§ Heads 1/2'-1' broad; leaves but slightly clasping. Involucre hemispheric, its bracts glandular.
27. A. oblongifolius.
Involucral bracts hispid or ciliate.
Leaves lanceolate to oblong-lanceolate, 4"-6" wide.