246 American Midland Naturalist Monograph No. 2 



59. Heads numerous, in spikes, racemes, or panicles. 



60. Heads in long terminal bracted spikes; receptacle bristly or chaffy; 



leaves opposite, or the upper alternate, entire or serrate 1. /va 



60. Heads in panicles or racemes; receptacle smooth; leaves alternate, 



mostly lobed or incised; plants bitter aromatic 44. Artemisia 



58. Staminate and pistillate flowers in separate dissimilar heads; involucre of 

 the pistillate heads woody or spiny. 

 61. Pistillate heads 1 -flowered; fruit an achene with 4-8 tubercles or straight 



teeth 2. Ambrosia 



61. Pistillate heads forming an ovoid bur covered with more or less hooked 

 prickles 3. Xanthnim 



57. Flowers yellow (or yellowish) or white. 



62. Flowers and bracts bright white; bracts petal-like, scarious-margined ; leaves 



alternate; stem woolly-pubescent; heads corymbose 35. H'^menopappus 



62. Flowers yellow or yellowish; bracts green. 



63. Heads numerous, in flat-topped corymbs; leaves alternate, pinnately 



dissected; plants bitter-aromatic 43. Tanaceiiim 



63. Heads few; leaves opposite. 



64. Pappus none; achenes thick, not flattened; disk-flowers perfect but 



sterile; plants glandular-pubescent 20. Polvmuia 



64. Pappus of 2-4 awns or teeth; achenes flattened; disk-flowers fertile; 

 plants not glandular 33. Bidens 



Series II. Liguliflorae DC. 



65. Pappus none; low glaucescent branching annual herbs with alternate clasping entire 



or lobed leaves, and few small long-peduncled heads of yellow flowers 



53. Serinia 



65. Pappus present. 



66. Pappus composed of scales, or of scales and bristles. 



67. Flowers yellow; pappus double, the outer of short thin scales, the inner of 

 bristles 55. Krigia 



67. Flowers blue (sometimes white or pink) ; pappus a short crown of numerous 



small chaffy scales 56. Cichorium 



66. Pappus consisting wholly of capillary bristles. 



68. Pappus plumose; leaves entire, grass-like; flowers yellow or purple 



54. Tragopogon 



68. Pappus not plumose. 



69. Heads usually several on each stem; leaves not all basal. 



70. Achenes more or less flattened; leaves usually lobed and often some- 

 what soft-prickly. 



71. Achenes narrowed at the apex, or beaked; flowers blue or yellow 

 57. Lactuca 



71. Achenes truncate, not teaked ; flowers yellow 58. Sonchus 



70. Achenes cylindric or prismatic. 



72. Flowers whitish or purjilish; heads jjendenl 59. Prcnanthcs 



72. Flowers yellow; heads erect. 



73. Achenes beakless 60. Hicracium 



73. Achenes t'lliform-beaked 62. Pyrrhopappiis 



69. Heads solitary; leaves all basal; flowers yellow. 



74. Achenes not muricate, 10-nerved; leaves (in our species) entire 



61. Agoseris 



74. Achenes muricate near the apex, 4-5-nerved; leaves lobed 



63. Taraxacum 



