Part 81 (1/2)

42. Iva. Achenes short, thick. Involucre of few roundish scales.

[+][+] Heads of two sorts on the same plant, the upper staminate with an open cup-shaped involucre, the lower pistillate, of 1--4 flowers in a closed bur-like involucre.

43. Ambrosia. Scales of staminate involucre united. Fruit 1-seeded.

44. Xanthium. Scales of staminate involucre distinct. Fruit 1--4-celled, 1--4-beaked.

[*] 3. Heads radiate, or rarely discoid; disk-flowers all perfect and fertile. Anthers blackish. Pappus none, or a crown or cup, or of one or two chaffy awns, never capillary, nor of several uniform chaffy scales.--Leaves more commonly opposite.

[+] Involucre double; the outer forming a cup.

45. Tetragonotheca. Outer involucre 4-leaved. Achenes obovoid; pappus none.

[+][+] Involucre of one or more rows of separate scales.

[++] Chaff of the flat receptacle bristle-shaped.

46. Eclipta. Ray short. Involucral scales 10--12, in two rows, herbaceous.

[++][++] Chaff scale-like, embracing or subtending the achenes.

[=] Receptacle high, conical or columnar in fruit. Pappus none or a short crown.

47. Heliopsis. Rays fertile. Achenes 4-sided. Leaves opposite.

48. Echinacea. Rays rose-colored, pistillate, sterile. Achenes short, 4-sided. Chaff spinescent.

49. Rudbeckia. Rays neutral. Achenes 4-sided, flat at the top, marginless.

50. Lepachys. Rays few, neutral. Achenes flattened laterally and margined.

[=][=] Receptacle flat to convex. Achenes not winged nor very flat.

51. Borrichia. Achenes 3--4-angled; pappus a short 4-toothed crown.

Shrubby.

52. Helianthus. Achenes flattened, bearing 2 very deciduous chaffy pointed scales.

[=][=][=] Receptacle convex (rarely conical). Achenes flat-compressed laterally, winged or wingless, 2-awned. Leaves decurrent.

53. Verbesina. Involucral scales closely imbricated in 2 or more rows.

54. Actinomeris. Scales few, soon deflexed. Achenes obovate, squarrosely spreading.

[*] 4. Rays few, neutral, or wanting. Achenes obcompressed, i.e., flattened parallel with the scales of the involucre (rarely terete).

Involucre double; the outer spreading and often foliaceous. Receptacle flat. Leaves opposite.

55. Coreopsis. Pappus of 2 (or rarely more) scales, teeth, or awns, which are naked or barbed upward, sometimes obsolete or a mere crown.

56. Bidens. Pappus of 2 or more rigid and persistent downwardly barbed awns or teeth.

57. Thelesperma. Inner involucre connate to the middle. Achenes terete.