125. CoMPOsiTAE 239 



plants annual; fields and waste places, common. Aug. -Oct. 

 Common Ragweed [A. clatior L.] A. artcmisiijolia X irifidn 

 Rouleau is occasionally found A. artemisiifolia L. 



2. Leaves sessile, pinnatifid; fruit imarmed or with blunt tuber- 



cles; plants perennial with a slender rhizome; roadsides and 

 waste places. July-Oct. Western Ragweed [A. psilostachya 



sensu A.Gray, non DC] A. coronopifolia V. & G. 



1. Leaves 3-to 5-lobed or undi\idecl; plants annual. 



3. Leaves opposite, 3- to 5-lobed, or entire; stem stout, 1-4 m tall; 



staminate heads peduncled; fruit with 5-7 sharp tubercles; 

 fields and waste places, common. July-Oct. Giant Ragweed 



A. trifida L. 



3. Leaves chiefly alternate, lanceolate, hastately toothed at ba.se; 

 stem 30-90 cm tall, rough-hirsute; staminate heads sessile, 

 the upper lobe of the involucre elongate, hispid; fruit with 

 4 teeth at the top; fields and waste places; chiefly in the 

 southern half of 111., extending northward to Menard Co. 

 A. bidcntata Michx. 



3. Franseria Cav. 



F. discolor Nutt. Adv. from the West ; La Salle and McHenry 

 counties. 



4. Xanthium L. — Cocklebur 



1. Leaves lanceolate, acute at each end, canescent beneath, each 

 with a 3-parted spine at the base; waste ground, rare; adv. 

 from trop. Am. ; Alexander, Cook, and Pulaski counties. Aug.- 



Oct. Spiny Cocklebur X. spinosum L. 



1 . Leaves cordate or ovate, the axils without spines. 



2. Bur ovoid to subglobose, less than twice as long as thick, merely 

 glandular; bottomlands, rare; Illinois R., Tazewell Co., (type 

 locality), F. H. Chase; Wayne Co., M. Walker in 1949 



- X. chasei Fern. 



2. Bur ellipsoid, more than twice as long as thick. 



3. Prickles numerous; body of the fruit and its prickles glandu- 

 lar-hispidulous; beaks hooked; waste places, cultixated 

 ground, and river banks. Aug.-Oct. {X . italicum sensu 

 auth., non Mor. ; X. saccharatum sensu Widder, ex ]:>.] 



X. commune Britt. 



3. Prickles relatively few; body of fruit glabrous or merely 

 glandular; beaks nearly straight; waste places, fields, and 

 along rivers. Aug.-Oct. [X. canadense sensu auth., non 

 Mill.; X. pungens Wallr. ; X. glahratum Britt.; X. pennsyl- 

 vanicum sensu auth., non Wallr.] X. chinense Mill. 



Tribe 2. J'ernonieae 



5. Vernonia Schreb. — Ironweed 

 1. Leaves glabrous beneath or merely puberulent. 



