30 KEY TO THE GENERA OF MANHATTAN PLANTS. 



12. Leaves, at least lower, opposite; akenes 5-angled Eupatorium 258 



12. Leaves alternate 13 



13. Bracts in 1 row, sometimes with a lew short outer ones 14 



13. Bracts in several rows 17 



14. Heads corymbose-clustered at summit, bracts in 1 row 15 



14. Heads soli tary on a scape Troximon 259 



14. Heads sessile along the rush like branches of the 



stem; leaves scale-like Lygodesmio 260 



14. Heads in a naked loose panicle 16 



15. Involucre 5-bracted, 5-flowered Cacalia 261 



15. Involucre several bracted, several flowered Senear* 262 



16. Involucre and peducle glandular Hieracium 263 



16. Involucre pubescent, not glandular Prenanthes 264 



17. Bracts appressed, yellowish, heads 3-8 mm high; 



pappus white Solidago 265 



17. Bracts loosely imbricated or spreading, green or 



greenish, heads larger 18 



18. Heads in wand-like spikes Laciniaria 266 



18. Heads corymbose-clustered or paniculate 19 



19. Pappus white, very plumose; akenes 5 mm Kuhnia 267 



19. Pappus brown or red, not plumose; akenes 2-3 mm Vernonia 268 



20. Involucre beset with hooks foiming a bur 21 



20. Involucre not bur-like 22 



21. Bur of numerous separate bracts; akenes several Arctium 269 



21. Bur indurated enclosing the 2 akenes. Xanthium 270 



22 Akene single, enclosed in a top-shaped, indurated 



involucre > Ambrosia 271 



22. Akenes several or numerous in each involucre 23 



23. Heads in close terminal spikes; pappus none Iva 272 



23. Heads not in spikes 23 



24. Very small, 2 4 mm high, panicled Artemisia 273 



24. Larger, 5 mm or more 25 



25. Receptacle naked (not chaffy) 26 



25. Receptacle chaffy 29 



26. Involucral bracts in several rows 27 



26. Bracts in about I row r , or with some short outer ones 28 



27. Pappus none; akenes terete,ribbed; heads H cm wide 



Chrysanthemum 274 



27. Pappus of 2 long bristles and several shorter ones; 



akenes flat; heads 7-10 mm wide Boltonia 275 



28. Pappus of scales dissected into bristles; plant resin- 



ous dotted Dysodia 276 



28. Pappus of several obovate, obtuse, scarious scales; 



plant woolly Hymenopappus 277 



29. Akenes strongly flattened and wing-margined 30 



