17. Oonopsis.

2. Heads with both ray-flowers and disk-flowers (in our species). a. None of the leaves cordate; pappus mostly as long as the achene, or longer. Leaves bristly-serrate or pinnatifid.

Achenes glabrous; pappus-bristles deciduous.

18. Prionopsis.

Achenes white-tomentose: pappus-bristles persistent.

19. Sideranthus.

Leaves entire, or toothed, not bristly-serrate.

Leaves narrow, coriaceous, evergreen, entire; low western undershrubs.

20. Stenotus.

Annual or perennial herbs; leaves not evergreen.

Pappus-bristles unequal; heads loosely panicled; annual.

21. Isopappus.

Pappus-bristles equal; heads variously clustered; perennial herbs.

Receptacle alveolate; rays mostly not more numerous than the disk-flowers.

22. Solidago.

Receptacle fimbrillate; rays more numerous than the disk-flowers; heads corymbose-paniculate.

23. Euthamia.

b. Lower and basal leaves cordate: pappus-bristles shorter than the achene.

24. Brachychaeta.

B. Ray-flowers present, not yellow in any of our species. * Pappus a mere crown, or of a few awns or bristles, or wanting, never of numerous capillary bristles.

1. Receptacle conic. Outer bracts of the involucre shorter than the inner; achenes prismatic.

25. Aphanostephus.

Bracts of the involucre all about equal; achenes flattened.

26. Bellis.

2. Receptacle flat, or somewhat convex.

Achenes of the disk-flowers compressed, of the ray-flowers 3-angled; perennial herbs with large heads.

27. Townsendia.

Achenes fusiform, terete: annual herbs with small heads.

28. Chaetopappa.

Achenes obovate, flattened, with thickened or winged margins; perennials.

29. Boltoma.

** Pappus of numerous capillary bristles.

1. Pappus a single series of capillary bristles; sometimes with an outer series of shorter ones.

a. Bracts of the involucre in 2 to many series.

Bracts mostly in 2-5 series; teeth or lobes of the leaves not bristle-tipped. Involucre narrow, its bracts firm: rays few, white.

30. Sericocarpus.

Involucre turbinate to hemispheric, bracts mostly thin; rays usually numerous, white to purple. Disk-flowers turning red, purple, or brown.

31. Aster.

Disk-flowers permanently white; leaves subulate to spatulate, crowded, rigid.

32. Leucelene.

Involucre turbinate; rays not exceeding the mature pappus, or none.

33. Brachyactis.

Bracts in many series; teeth or lobes of the leaves bristle-tipped in our species.

34. Machaeranthera.

b. Bracts of the involucre mostly in 1 or 2 series, very narrow; heads mostly long-peduncled. Rays longer than the diameter of the disk.

35. Erigeron.

Rays not longer than the diameter of the disk; heads very small, panicled.

36. Leptilon.

2. Pappus distinctly double, the inner bristles long, the outer shorter. Leaves lanceolate, ovate, or obovate: rays white.

37. Doellingeria.

Leaves narrowly linear; rays violet.

38. Ionactis.

C. Ray-flowers none; dioecious shrubs; pappus capillary.

39. Baccharis.

Tribe 4. Inuleae.

* Heads small, rays none; flowers white, or whitish.

1. Receptacle chaffy. Receptacle convex; pappus none.

40. Filago.

Receptacle subulate; pappus of the inner flowers of rough capillary bristles.

41. Gifola.

2. Receptacle naked. a. Pappus, at least that of pistillate flowers, of capillary bristles. Bracts of the involucre not scarious; plants pubescent or glabrous, not woolly.

42. Pluchea.

Bracts of the involucre scarious, mostly white or pink; plants woolly. Plants dioecious, or polygamo-dioecious.

Pappus-bristles of staminate flowers thickened above.

43. Antennaria.

Pappus-bristles not thickened; stem leafy.

44. Anaphahs.

Plants not dioecious; flowers all fertile.

45. Gnaphalium.

b. Pappus none: leaves broad, alternate, woolly beneath.

46. Adenocaulon.

** Heads large; ray-flowers yellow.

47. Inula.

Key to Genera.

Tribe 5. Heliantheae. A. Disk-flowers perfect, but sterile.

Achenes thick, short, not flattened; pappus none.

Achenes merely subtended by the inner involucral bracts.

48. Polymnia.

Achenes embraced and enclosed by the inner involucral bracts. Involucral bracts unarmed.

49. Melampodium.

Involucral bracts armed with hooked prickles.

50. Acanthospermum.

Achenes flattened.

Ray-flowers in 2 or 3 series; achenes falling away free.

51. Silphium.

Ray-flowers in 1 series; achenes adnate to 2 or 3 scales of the receptacle, falling away with them. Rays large, yellow.

Leaves opposite and basal.

52. Chrysogonum.

Leaves alternate.

Pappus none, or of 2 caducous awns.

53. Berlandiera.

Pappus a persistent irregularly cleft crown.

54. Engelmannia.

Rays small, the head appearing discoid.

55. Parthenium.

B. Disk-flowers fertile. * Ray-flowers persistent upon the achenes.

Achenes compressed, or 3-angled; leaves entire.

56. Crassina.

Achenes short, thick; leaves toothed.

57. Hehopsis.

** Ray-flowers deciduous, or none.

† Pappus a cup, or crown, or of a few teeth, awns, or bristles.

1. Achenes, at least those of disk-flowers, not compressed (except in Ratibida and Phaethusa); scales of the receptacle mostly concave, or clasping.

Scales of the receptacle small, awn-like or bristle-like; rays white, short.

58. Verbesina.

Scales of the receptacle broad, larger.

Involucre of 4 large somewhat united bracts.

59. Tetragonotheca.

Involucre of several or numerous separate bracts. Receptacle conic, or columnar.

Ray-flowers fertile, or wanting; leaves opposite.

• 60. Spilanthes.

Ray-flowers sterile, or neutral; leaves mostly alternate. Rays yellow.

Achenes 4-angled or terete. Achenes 4-angled.

61. Rudbeckia.

Achenes terete: leaves cordate-clasping.

62. Dracopis.

Achenes compressed, winged.

63. Ratibida.

Rays rose-purple or yellow.

64. Echinacea.

Receptacle flat, or convex (low-conic in species of Nos. 66 and 68). Low fleshy sea-coast shrubs.

65. Borrichia.

Tall herbs, not fleshy.

Achenes not much flattened, not winged, nor margined.

66. Helianthus.

Achenes of disk-flowers flattened and margined, or winged. Involucre of a few deflexed bracts.

67. Ridan.

Involucre of 2 series or more of appressed or spreading bracts. Perennials: bracts erect or appressed.

68. Phaethusa.

Annuals; bracts spreading.

69. Xitnenesia.

2. Achenes very flat; scales of the receptacle flat, or but slightly concave. a. Bracts of the involucre all separate. Pappus of 2 short teeth or awns, or a mere border, or none.

70. Coreopsis.

Pappus of 2-6 awns or teeth, upwardly or downwardly barbed or hispid. Achenes flat, or angled.

71. Bidens.

Achenes terete: aquatic, the submerged leaves filiform-dissected.

72. Megalodonta.

b. Inner bracts of the involucre united to about the middle.

73. Thelesperma.

†† Pappus of numerous scales. Leaves opposite, toothed; ray-flowers fertile; rays small.

74. Galinsoga.

Leaves alternate, entire.

Rays large, neutral; receptacle deeply honey-combed.

75. Endorima.

Rays none; scales of the receptacle narrow, rigid.

76. Marshallia.

Tribe 6. Helenieae.

A. Ray-flowers persistent on the achenes, falling away with them, papery.

77. Psilostrophe.

B. Ray-flowers deciduous, or wanting. * Plants not dotted with oil-glands.

a. Pappus none.

78. Flaveria.

b. Pappus present (in all our species), of separate scales or bristles. 1. Bracts of the involucre petal-like, colored, their margins and apices scarious. Leaves, at least the lower, pinnately parted, or pinnatifid; rays none; corolla-lobes of disk-flowers ovate.

79. Hymenopappus.

Leaves entire; rays present, or none: corolla-lobes of disk-flowers linear.

80. Othake.

2. Bracts of the involucre herbaceous, not scarious-tipped, nor petal-like, appressed, or spreading. Receptacle naked.

Bracts of the involucre appressed. Achenes 4-angled, linear or oblong.

81. Picradeniopsis.

Achenes 5-10-ribbed or 5-10-angled, top-shaped. Involucral bracts separate to the base.

82. Tetraneuris.

Outer involucral bracts connate.

83. Hymenoxys.

Bracts of the involucre spreading, or reflexed at maturity.

84. Helenium.

Receptacle with bristle-like chaff.

85. Galliardia.

** Plants dotted with oil-glands, especially the leaves and involucre.

Involucral bracts more or less united; style-branches of the disk-flowers elongated. Involucral bracts united at the base.

86. Boebera.

Involucral bracts united high up into a cup.

87. Thymophylla.

Involucral bracts separate; style-branches of the disk-flowers very short.

88. Pectis.

Tribe 7. Anthemideae.

* Receptacle chaffy.

Achenes flattened; involucre obovoid to campanulate; heads small.

80. Achillea.

Achenes terete; involucre hemispheric; heads large.

90. Anthemis.

** Receptacle not chaffy, naked, or sometimes hairy. 1. Ray-flowers usually present, sometimes wanting. Receptacle flat to hemispheric; bracts of the involucre in several series.

91. Chrysanthemum.

Receptacle conic to ovoid; bracts in few series.

92. Matricaria.

2. Ray-flowers none; heads small. Heads corymbed; pappus a short crown; flowers yellow.

93. Tanacetum.

Heads racemose, spicate or panicled; pappus none.

94. Artemisia.

Tribe 8. Senecioneae.

Leaves all basal; heads on scapes. Heads solitary; flowers yellow.

95. Tussilago.

Heads corymbed; flowers white or purple.

96. Petasites.

Leaves opposite; rays yellow.

Involucre of several thin herbaceous bracts.

97. Arnica.

Involucre of 4 or 5 broad fleshy bracts.

98. Haploesthes.

Leaves alternate.

Flowers white, whitish or pinkish; rays none.

Marginal flowers pistillate: disk-flowers perfect.

99. Erechtites.

Flowers all perfect.

Involucre of about 5 bracts; sap milky.

100. Mesadenia.

Involucre of about 12 bracts and several smaller outer ones.

101. Synosma.

Flowers yellow; ray-flowers mostly present.

102. Senecio.

Tribe 9. Cynareae.

* Achenes inserted on the receptacle by their bases, not oblique.

Receptacle densely bristly. Filaments separate.

Involucral bracts hooked at the tip; leaves not bristly.

103. Arctium.

Involucral bracts not hooked; leaves bristly. Pappus-bristles plumose.

104. Cirsium.

Pappus-bristles not plumose.

105. Carduus.

Filaments united below.

106. Mariana.

Receptacle fleshy, not bristly.

107. Onopordon.

** Achenes obliquely inserted on the receptacle. Heads not subtended by bristly leaves; involucral bracts often bristly.

108. Centaurea.

Heads sessile, subtended by bristly leaves.

109. Cnicus.