MACLOSKIE : COMPOSITE. 769 



c. Involucral scales of hermaphrodite (male) heads connate, forming I series of spines or 



tubercles. 34. Ambrosia, p. 820. 



c2. Involucral scales of hermaphrodite (male) heads free. 35. Xanthium, p. 821. 

 l>2. Corolla of female flowers none or normal. Heads hermaphrodite, homogamous or het- 



erogamous. Rays none, or withering, or deciduous before ripening of the fruit. 

 c. Disk-flowers sterile. Achenes dorsally compressed, surrounded by an inner involucral 

 scale, and by 2(~3) neighboring pales, which enclose the hermaphrodite flowers. 

 Corolla very short. Head erect. Fruits naked or nearly so, their ribs united with 

 the pales. 33. Parthenium, p. 820. 



cz. Disk-flowers fertile. Pappus of retrorsely rough bristles. 



d. Achenes not, or laterally, compressed. Inner involucral scales plane. 



e. Pales very small. Pappus none or 2 short awns. Marginal flowers small, 

 more or less 2 -seriate. Ligules entire or 2-toothed. 



36. Eclipta, p. 822. 

 e2. Pales broad, arched or complicate, more or less enclosing the hermaphrodite 



flowers, but not the ripe achenes. 



/. Fruit of hermaphrodite flowers, thick, 4~5-angled, or somewhat dorsally 

 compressed (of the marginal female flowers, often 3 -angled or dorsally 

 compressed). Involucral scales exceeding 4, free, mostly subsimilar. 

 Pappus-scales basally united or free, with or without 15 small awns. 

 Achenes obscurely or obtusely 4-angled. Herbs or shrubs with opposite 

 leaves. 37. Wedclia, p. 822. 



/2. Fruit of disk-flowers flat-compressed, with acute or winged angles, un- 

 stalked. Heads many- (20 -f ) flowered. Pappus of 2 awns, with no 

 intermediate scales. 



g. Ripe achenes not winged. Ray-flowers female or none. Receptacle 

 conical. Herbs with opposite leaves and solitary erect heads. 



38. Spilanthes, p. 823. 



g2. Ripe achenes winged from the base, not diverging from each other. 

 Mostly herbs, with leaves often decurrent. 



39. Verbesina, p. 823. 



d2. Achenes more or less laterally compressed. Inner involucral scales connate, at 

 least halfway. Heads stalked or rarely numerous and sessile. Style-append- 

 ages of the hermaphrodite flowers none or short. Achenes similar, or the 

 marginal reduced. Smooth undershrubs ; lower leaves opposite. 



40. Thelespenna, p. 824. 

 A2. Receptacle centrally without chaff, with i-seriate pales subtending the outer hermaphrodite 



flowers. Achenes of female flowers laterally compressed (rarely no ray flowers). Herbs 

 mostly with alternate, entire leaves. 41. Madia, p. 824. 



Tribe VI. Helenioidea. (Genera 42-47), p. 825. 



A. Plant without oil-glands. Hermaphrodite flowers fertile. Achenes not flat-compressed, or 



at least with lateral nerves. 



b. Receptacle flat or convex, rarely hemispherical. 

 c. Pappus none. 



