168 
4+ 4+ Involucre broad: achenes mostly much flattened. 
42. Silphium. Achenes wing-margined, in several rows: pappus none or 2 teeth: 
involucral scales thick, in several rows. 
43. Berlandiera. Achenes wingless, 5 to 12 in one row, without pappus: inner 
involucral scales obovate, outer smaller and more leaf-like. 
44. Lindheimera. Achenes wing-margined, 4 or 5 in one row, the wings confluent 
at apex with 2 triangular teeth, and a smaller tooth projecting from the promi- 
nent rib: outer involucral bracts (4 or 5) lenf-like, imer larger and herbaceous be- 
coming chartaceous: upper leaves opposite. 
45, Engelmannia. Achenes wingless, 8 to 10 in one row: pappus a scarious his- 
pid crown: outer involucral bracts (about 10) leaf-like, inner coriaceous with green 
tips: leaves alternate. 
46. Parthenium. Rays 5, very short, persistent: pappus of 2 small scales: invo- 
lucral bracts short, roundish, in 2 rows. 
* * Fertile flowers 1 to 5, the corolla none or reduced to atube: staminate corolla 
funnelform: pappus none. 
+ Heads with 1 to 5 pistillate flowers: receptacle chafty. 
47, Iva. Achenes short and thick: involucre of few roundish bracts. 
~ + Heads of two sorts on the same plant, the staminate with an open cup- 
shaped involucre, the pistillate of1 to 4 flowers in a closed bur-like involucre. 
++ Bracts of staminate involucre united: receptacle low. 
48, Hymenoclea. Anther-tips blunt: involucre of the solitary fertile flower 
beaked at apex, the lower part with 9 to 12 dilated and silvery-scarious persistent 
transverse wings. 
49. Ambrosia. Anther-tips setiferous-acuminate: involucre of the solitary fer- 
tile flower nut-like, beaked at apex, usually armed with 4 to & tubercles or short 
spines in a single series below the beak. 
50. Franseria. Anther-tips setiferous-acuminate: fertile involucre 1 to 4-flow- 
ered, 1 to 4-beaked, more or less bur-like, being armed over the surface with several 
or numerous prickles or spines in more than one series. 
w+ ++ Bracts of staminate involucre distinct: receptacle cylindraceous. 
51. Xanthium. Hertile heads a closed bur-like 2-flowered involucre 1 or 2- 
beaked at apex, the surface clothed with hooked prickles, the 2 thick ovoid achenes 
permanently inclosed in the indurated prickly involucre, 
** * Ray-flowers ligulate and fertile ; the ligule persistent on the achene and becom- 
ing papery: the numerous disk-flowers perfect and fertile, subtended or em- 
braced by chaffy bracts: corolla cylindraceous: leaves opposite, and heads 
singly terminating stems or branches. 
52. Zinnia. Involucre campanulate or cylindraceous: rays showy: lobes of disk- 
corolla mostly velvety-villous:. achenes wingless or nearly so; of the ray 3-sided, 
of the disk much compressed: pappus (when present) of erect awns or chaffy teeth: 
leaves mostly sessile. 
53. Sanvitalia. Involucre short and broad: ligules often short and small: disk- 
corollas with glabrous lobes: achenes of ray commonly 3-sided, the angles produced 
into as many rigid divergent awns; of the disk often heterogeneous, from com- 
pressed-quadrangular to flat, some usually wing-margined, the pappus of 1 or2 slender 
awns or teeth or none: leaves commonly petioled. 
~*** Heads radiate or rarely discoid, the disk-flowers all perfect and fertile: anthers 
blackish: pappus none, or a crown or cup, or of 1 or 2 chaffy awns, never 
capillary nor of several uniform chafty scales, 
+ Involuere double, the outer forming a cup. 
54. Tetragonotheca. Outer involucre 4-leaved: achenes obovoid: pappus none, 
