COMPOSITE 335 



5, the anthers united around the 2 styles: fruit dry and 1-seeded, 

 indehiscent, usually crowned with a pappus which represents a 

 calyx. The largest of all phenogamous families, comprising about 

 one-tenth of all flowering plants, about 800 genera and 11,000 to 

 12,000 species. Common composites are sunflower, aster, goldenrod, 

 boneset, dahlia, chrysanthemum, marigold, compass plant, thistles, 

 dandelion, lettuce. 



A. Head with all the flowers strap-shaped (with rays) and 

 perfect: juice milky: leaves alternate. 



B. Flowers yellow 1. Taraxacum 



BB. Flowers blue or pink 2. Cichorium 



AA. Head with tubular and mostly perfect disk flowers, the 

 rays, if any, formed of the outer strap-shaped and 

 imperfect flowers. In cultivated species, all the 

 flowers may become strap-shaped (head double ") : 

 juice not milky. 



B. Fruit a completely closed and bur-like involucre, 

 containing one or two small akenes : flowers 

 imperfect. 



C. Involucre-bur large and sharp-spiny 3. Xanihium 



cc. Involucre-bxir small, not sharp-spiny 4. Ambrosia 



BB. Fruit not formed of a closed and hardened involucre 

 (although the involucre may be spiny, as in 

 Arctium and Cnicus). 

 c. Pappus none. 



D. Leaves opposite, simple 5. Ageratum 



DD. Leaves alternate. 



E. Foliage finely divided 6. Achillea 



EE. Foliage entire, toothed or broad-lobed. 



p. Akenes curved or horseshoe-shaped .... 7. Calendula 

 PP. Akenes straight. 



G. Torus flat or slightly convex 8. Chrysanthemtim 



GG. Torus conical 9. ftudbeckia 



cc. Pappus of 2 thin early deciduous scales 10. ffelianthus 



ccc. Pappus a short crown 11. Tanacetum 



cccc. Pappus of many bristles. 



D. Plant very prickly 12. Cnicus 



DD. Plant not prickly. 



E. Involucre prickly and bur-like 13. Arctium 



EE. Involucre not a bur nor prickly. 



p. Torus bristly (chaff or bracts amongst 



the florets) 14. Centaurea 



PP. Torus naked. 

 G. Rays present. 



H. Color yellow, the heads very small.. 15. Solidago 

 HH. Color not yellow. 



i. Scales of involucre unequal 16. Aster 



n. Scales equal in length 17. Erlgeron 



in. Scales in several rows, more or 



less leafy 18. Callistephus 



GG. Rays none 19. Eupatorium 



