18. A. azùreus, Lindl. Stem rather rough, erect, racemose-compound at the summit, the branches slender and rigid; leaves rough, the lower ovate-lanceolate or oblong, heart-shaped, on long often hairy petioles; the others lanceolate or linear, sessile, on the branches awl-shaped; involucre inversely conical.—Copses and prairies, western N. Y., and Ohio to Minn., and southwestward. Involucre much as in A. lævis, but smaller and slightly pubescent.
19. A. Shórtii, Hook. Stem slender, spreading, nearly smooth, bearing very numerous heads in racemose panicles; leaves smooth above, minutely pubescent underneath, lanceolate or ovate-lanceolate, elongated, tapering gradually to a sharp point, all but the uppermost more or less heart-shaped at base, and on naked petioles, none clasping; involucre bell-shaped.—Cliffs and banks, Ohio to Ill., and southward.—A pretty species, 2–4° high; leaves 3–5´ long.
20. A. undulàtus, L. Pale or somewhat hoary with close pubescence; stem spreading, bearing numerous heads in racemose panicles; leaves ovate or ovate-lanceolate, with wavy or slightly toothed margins, roughish above, downy underneath, the lowest heart-shaped on margined petioles, the others abruptly contracted into short broadly winged petioles which are dilated and clasping at the base, or directly sessile by a heart-shaped base; involucre obovoid, the scales less rigid.—Dry copses; common.
[++][++] Leaves conspicuously serrate; heads small; rays pale blue or nearly white.
21. A. cordifòlius, L. Stem much branched above, the spreading or diverging branches bearing very numerous panicled heads; lower leaves all heart-shaped, on slender and mostly naked ciliate petioles; scales of the inversely conical involucre all appressed and tipped with very short green points, obtuse or acutish.—Woodlands; very common.—Heads profuse, but quite small. Varies with the stem and leaves either smooth, roughish, or sometimes hairy, also with the leaves all narrower. Apparent hybrids with n. 35 also occur.
22. A. sagittifòlius, Willd. Stem rigid, erect, with ascending branches bearing numerous racemose heads; leaves ovate-lanceolate, pointed; the lower heart-shaped at base, on margined petioles; the upper lanceolate or linear, pointed at both ends; scales of the oblong involucre linear, tapering into awl-shaped slender and loose tips.—Dry ground, N. Y. and Penn. to Ky., and northward.—Green, but usually more or less hairy or downy; the heads rather larger than in the last, almost sessile.
23. A. Drummóndii, Lindl. Pale with fine gray pubescence; leaves cordate to cordate-lanceolate, mostly on margined petioles, the uppermost lanceolate and sessile; scales acute or acutish.—Passing into the last. Open ground, etc., Ill. to Minn. and Kan.
24. A. Lindleyànus, Torr. & Gray. Rather stout, 1–2° high, sparsely pubescent or nearly glabrous; radical and lowest leaves ovate, moderately or obscurely cordate, the uppermost sessile and pointed at both ends; heads larger, rather few in a loose thyrse or panicle, the linear-attenuate scales looser and less imbricated; rays pale violet.—Lab. to L. Superior; Lisbon, N. H. (C. E. Faxon), and Mt. Desert (Rand).
[*] 6. Without heart-shaped petioled leaves, the radical and lower all acute or attenuate at base; not glandular nor viscid, nor silky-canescent.
[+] Smooth and glabrous throughout (or nearly so, except forms of n. 29), and usually pale and glaucous; involucral scales closely imbricated, firm and whitish-coriaceous below, green-tipped; leaves firm, usually entire.