18. Iva. Marginal pistillate florets 1-5, with very small tubular corolla or none. Staminate florets with funnel-form 5-toothed corolla. Anthers nearly separate. Achenes very short. Coarse plants with small greenish-white nodding heads. N. W.
B. Rays or strap-shaped corollas round the margin of the head.
* Pappus of hair-like bristles. Receptacle naked.
19. Sene'cio. Rays yellow, or in one species none. Scales of the involucre in a single row, or with a few bractlets at the base.
Pappus very fine and soft. Heads corymbose. Leaves alternate.
20. In'ula. Rays yellow, numerous, very narrow, in a single row Outer scales of the involucre leaf-like. Anthers with two tails at the base. Stout plants, with large alternate leaves which are woolly beneath.
21. Chrysop'sis. Rays yellow, many. Disk yellow. Pappus double, the outer of very small chaffy bristles, the inner capillary. Low hairy herbs. - N.W. only.
22. Aplopap'pus. Rays yellow, many. Disk yellow. Pappus simple, of unequal bristles. - N. W. only.
23. Sollda'go. Rays yellow, few, as are also the disk-florets. Involucre oblong, scales of unequal lengths, appressed. Achenes many-ribbed. Heads small in compound racemes, or corymbs. Stems usually wand-like. Leaves alternate.
21. Ar'nica. Rays yellow. Disk yellow. Scales of the bell-shaped involucre in two rows, lanceolate, erect. Receptacle flat, minutely fringed. Achenes slender. Leaves opposite. Heads showy, with long peduncles. Stem simple.
25. Tussila'go. Rays yellowish, in several rows, very narrow.
Involucre nearly simple. Pappus copious, soft. A low perennial, with creeping rootstocks, sending up a scaly scape in early spring bearing one head, and producing later heart-shaped angled or toothed leaves, woolly when young.
26. Petasi'tes. Rays whitish or purplish. Heads in a corymb, fragrant. Scales of the involucre in a single row. Heads somewhat dioecious, the staminate with one row of pistillate ray-flowers, the pistillate with ray-flowers in many rows. Woolry herbs, with large leaves, all radical, and sheathing scaly bracts on the scape.
27. Aster. Rays white, purple, or blue, never, yellow, but the disk generally yellow. Pappus of numerous fine roughish bristles, (in one species double). Achenes flattish. Heads corymbed or racemose. Flowering in late summer.
28. Erig'eron. Rays and disk as in Aster, but the rays very narrow, and usually in more than one row. Scales of the involucre in one or two rows, nearly of equal length. Pappus of long bristles with shorter ones intermixed. Heads corymbed or solitary. Leaves generally sessile.
* * Pappus not of hair-like bristles, but either altogether wanting or consisting of a few chaffy scales or teeth, or only a minute crown.
+ Receptacle naked.
29. Grinde'lia. Rays yellow, many. Disk yellow. Heads large.
Pappus of 2 or 3 rigid awns, falling off early. Scales of the involucre with spreading tips. Coarse herbs with sessile serrate leaves. - N.W. chiefly.
30. Gutierre'zia. Rays yellow, few. Disk-florets 3 or i. Heads numerous, small, crowded. Pappus of a few short chaffy scales. A low partly shrubby plant, with narrowly linear entire alternate leaves. N.W. only.
31. Hele'nium. Rays yellow, wedge-shaped, 3-5-cleft at the summit.
Scales of the involucre reflexed, awl-shaped. Pappus of 5-8 chaffy scales, 1-nerved, the nerve usually extending to a point. Leaves alternate, decurrent on the angled stem. Heads corymbed, showy.
32. Chrysan'themum. Rays white; disk yellow. Disk-corollas with a flattened tube. Pappus none. Heads single, or corymbed. Involucre broad and flat, the scales with scarious margins. Receptacle flattish.
33. Belli*. Rays white or pink, numerous. Scales of the involucre in about 2 rows. Receptacle conical, naked. Low herbs with solitary heads on scapes. Escaped from cultivation.
34. Matricaria. Rays white, disk yellow. Receptacle conical.
Achenes 3-5-ribbed. Pappus a short crown or border.
+ + Receptacle chaffy.
36. An'themis. Rays white. Disk yellow. Ray florets pistillate or neutral. Pappus none or a minute crown. Receptacle conical more or less chaffy. Herbs with strong odour, and pinnately dissected leaves. Heads terminal.
36. Rudbeck'ia. Rays yellow, usually long; disk dark-purple, or in one species greenish-yellow. Scales of the involucre leaf-like. Receptacle conical. Pappus none, or only a minute crown. Ray-florets neutral.
37. Helian'thus. Rays yellow, neutral. Receptacle flattish or convex. Chaff persistent, and embracing the 4-sided achenes. Pappus deciduous, of 2 thin scales. Stout coarse herbs.
38. Actlnom'eris. Rays 2-8, irregular, yellow, neutral. Receptacle small, convex. Scales of the involucre few, soon deflexed. Achenes flat, obovate, spreading when ripe. Pappus of 2 or 3 smooth awns, persistent. Tall branching perennials, with mostly decurrent leaves.
39. Coreop'sis. Rays mostly 8, yellow (sometimes brown-tinted), neutral. Receptacle flat. Involucre doable, each of about 8 scales, the outer leaf-like and spreading, the inner rather membranaceous and appressed. Achenes flat, compressed parallel with the scales of the involucre, 2-toothed or sometimes naked. Heads corymbed.
40. Gaillard'ia. Rays yellow (sometimes purplish), numerous, 3cleft. Receptacle convex, the chaff bristly or awl-shaped. Achenes top-shaped, 5-ribbed. Pappus of several long thin scales, awn-tipped. Heads showy, fragrant, terminal, on scapelike stems. - N.W.
41. Bidens. Rays yellow, few; but 2 species are without rays. Scales of the involucre in 2 rows, the outer large and leaf-like. Ray-florets neutral. Achenes crowned with 2 or more stiff awns which are barbed backward. .
42. Heliop'sis. Rays yellow, 10 or more, pistillate. Scales of the involucre in 2 or 3 rows, the. outer leaf-like. Receptacle conical; chaff linear, Achenes smooth, 4-angled. Pappus none.
43. Achillea. Rays white (occasionally pinkish), few. Receptacle flattish. Pappus none. Achenes margined. Heads small, in flat corymbs. Leaves very finely dissected.
44. Polym'nia. Rays whitish-yellow, wedge-form, shorter than the involucre, few in number. Scales of the involucre in 2 rows, the outer leaf-like, the inner small, and partly clasping the achenes. Pappus none. Coarse clammy herbs with an unpleasant odour.
45. sil'phium. Easily known by its stout square stem, and the upper connate leaves forming a sort of cup. Flowers yellow. Achenes broad and flat.