This section is from the book "Wild Flowers Of New York", by Homer D. House. Also available from Amazon: Wild Flowers Of New York.
Aster The Wild Asters comprise a genus of over two hundred and fifty species, of which nearly fifty species occur in New York State. They are mostly perennial, branching herbs with alternate, simple leaves and corymbose or paniculate heads of both tubular and radiate flowers. Involucre varying from hemispheric to campanulate or turbinate, with its bracts overlapping in several series, the outer ones usually shorter and smaller. Ray flowers white, pink, purple, blue or violet, pistillate. Disk flowers perfect, tubular, their corollas five-lobed, usually yellow and changing to red, brown or purple; pappus bristles slender, numerous, rough or minutely toothed, usually in one, sometimes in two series; achenes mostly flattened and nerved.
Key to the New York Species of Aster .4 Basal and lower leaves, or some of them, cordate and slender petioled Stem leaves, or some of them, cordate-clasping; plant rough when dry..........
1 A. undulatus None of the stem leaves cordate-clasping; rays white, violet or rose
Rays white or rarely rose, usually two-toothed; plants not glandular
Involucre ovoid, campanulate or turbinate: its bracts mostly obtuse or rounded; basal leaves few and small, or commonly none (except A. glomeratus) Leaves membranous or thin, smooth or nearly so
Heads short-peduncled, three-fourths of an inch broad or less, the disk turning crimson; leaves acute or short-acuminate
2 A. carmesinus
Heads long-peduncled, three-fourths of an inch broad or more, the disk turning brown or reddish; leaves long-acuminate
Heads 1 inch broad or more; leaves of the branches large, long, lanceolate, acuminate.......3 A. tenebrosus
Heads three-fourths to 1 inch broad; leaves of the branches small, obtuse or acute..........4 A. divaricatus
Leaves thick, firm, rough; heads one-third to one-half of an inch 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. sehreberi Rays violet, usually three-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
Inflorescence very irregular, paniculate-corymbose; plants often 4 to 5 feet high; broader leaves large, cordate, acute .11 A.nobilis Inflorescence rather regular, flat, or convex-topped; plants usually less than 2' feet tall
Sinus broad and shallow
Broader leaves orbicular-cordate, their teeth and the inflorescence-leaves inconspicuous. .12 A. ianthinus Broader leaves reniform, sharply incised; some inflorescence-leaves conspicuous.................13A. violaris
Sinus rather deep and narrow; broader leaves ovate-cordate, sharply serrate...................14 A. multiformis
Rays blue or purple; plants not glandular; bracts of the involucre appressed or nearly so; rays eight to twenty Leaves all entire, or nearly so, thick and firm, rough-puberulent on both sides, the upper bractlike...................15 A. azureus
Leaves nearly all sharply serrate and thin
Heads 2 to 3 lines high, numerous; bracts obtuse or bluntish
Leaves rough; petioles not wing-margined; bracts appressed. .
16 A. cordifolius Leaves smooth, or nearly so; petioles, or some of them wing-margined.....................17 A. 1 owrieanus
Heads 4 to 5 lines high, usually few; bracts acute or acuminate. . . .
18 A. lindleyanus Heads 3 to 5 lines high, numerous; bracts acute or acuminate; stems glabrous or nearly so; bract-tips spreading...............
19 A. sagittifolius 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. tardi-florusand sometimes in A. laevis) Stem rough, or hirsute-pubescent
Leaves, at least the lower, sen-ate; stem hispid-pubescent; bracts glabrous or ciliate.........................................20 A. puniceus
Leaves entire, oblong, linear or lanceolate
Heads one-half to 1 inch broad, the linear to linear-lanceolate leaves but slightly clasping; bracts hispid or ciliate
21 A. amethystinus Heads 1 to 2 inches broad; leaves sessile and strongly clasping
Stems hirsute; leaves lanceolate; involucre hemispheric; bracts viscid............................22 A. novae-angliae
Stems rough; leaves oblong to lanceolate; involucre turbinate
Leaves thick, firm, very rough, oblong to oval..............
23 A. patens
Leaves thin, roughish, oblong-lanceolate....................
24 A. phlogifolius Stem glabrous, or only sparingly pubescent above Leaves sharply serrate
Leaves tapering to the base
Leaves narrowed to the base, the lower into winged petioles......
25 A. tardiflorus
Leaves scarcely or gradually narrowed at the base.................
20 A. puniceus Leaves abruptly contracted into margined petioles, often enlarged near the base..............................26 A. prenanthoides
Leaves usually strongly cordate-clasping; bracts green-tipped........
27 A. laevis Leaves entire or nearly so
Involucre campanulate, its bracts appressed, green-tipped
Stem leaves oblong, lanceolate or oval-lanceolate. .27 A. laevis
Stem leaves elongated-lanceolate............28 A. concinnus
Involucre hemispheric
Bracts in one or two series; leaves linear to lanceolate............
29 A. longifolius Bracts in several series, unequal
Bracts linear-subulate; leaves narrowly linear...............
30 A. junceus
Bracts lanceolate, leaves lanceolate, 2 to 6 inches long........
31 A. novi-belgii C Leaves sessile or petioled, scarcely or not at all clasping
Leaves silky or silvery-canescent, entire; heads in a narrow raceme; bracts linear
32 A. concolor Leaves neither silvery, silky nor canescent; leaves entire or toothed Bracts of the involucre with herbaceous tips
Tips of the involucral bracts spreading (little spreading in A. radula , erect or spreading in A. herveyi); heads large, showy; rays violet to purple
Leaves oblong-lanceolate, sharply serrate, rugose, the basal leaves usually wanting.............................33 A. radula
Leaves lanceolate to oblong, the lower sparingly dentate
Basal leaves with unmargined petioles......34 A. hervevi
Basal leaves with margined petioles, bracts glandular........
35A. spectabi 1 i s Involucral bracts all appressed (except in A. multiflorus, a small-headed species); rays mostly white, sometimes purple Heads unilaterally racemose
Stem leaves oval, oblong, or lanceolate, serrate, or chiefly so
Stem pubescent or glabrate......36 A. lateriflorus
Stem villous; leaves narrowly lanceolate, thin..........
37 A. hirsuticaulis Stem leaves linear-lanceolate to linear, nearly entire; stem glabrate.............................38 A. vimineus
Heads not unilaterally racemose, mostly paniculate
Involucral bracts spatulate, mostly ciliate, somewhat spreading, at least the outer ones obtuse; plants roughish-puberulent
39 A. multiflorus Involucral bracts appressed, acute
Heads solitary at the ends of very small-leaved branchlets
40 A. dumosus Heads paniculate
Stem leaves lanceolate, serrate or entire Heads 8 to 10 lines broad
Plants glabrous, or sparingly pubescent above
Leaves firm, roughish or rough; rays often purplish; involucral bracts acute
41 A. salicifolius
Leaves thin, smoothish; rays chiefly white; involucral bracts acuminate. . .
42 A. paniculatus Plant puberulent all over.................
43 A. tradescanti
Heads 6 to 8 lines broad; stem leaves narrowly lanceolate............43 A. tradescanti
Stem leaves linear-lanceolate to subulate, mostly entire Heads scattered, 6 to 9 lines broad; upper leaves linear.......................44 A. faxoni
Heads numerous, 4 to 7 lines broad; upper leaves subulate; involucre subhemispheric, 21/2 to 3 lines high; rays usually white
Paniculately branched, bushy..............
45 A. ericoides Simple, or with slender ascending branches
46 A. pring1ei Bracts of the involucre without herbaceous tips Bracts linear-subulate, acuminate
Leaves firm, 3 inches long or less, entire or sparingly serrate......
47 A. nemoralis
Leaves thin, 6 inches long or less, sharply serrate................
48 A. acuminatus Bracts oblong or oblong-lanceolate, obtuse or acutish; leaves narrow, entire..................................49 A. ptarmicoides
D Leaves fleshy, narrow, entire; plants of salt marshes or saline soil
Perennial; heads 6 to 12 lines broad; involucral bracts lanceolate, acuminate.....
50 A. tenuifolius
Annual; heads 3 to 5 lines broad; involucral bracts linear-subulate; disk flowers fewer than the very short rays........................51 A.subulatus
 
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