Jones: hLORA of Illinois, 152. Compositae 247 



Tribe 1. Ambrosieae 

 1. IvA L. — Marsh-elder 



1. Heads in bracted spikes; stem hispid; fields and roadsides. Aug.-Oct 



/. altata Willd. 



1. Heads spicate-paniculate; stem puberulent; roadsides and fields. July-Seot. 



Horseweed. [Cyclachaena xanthifolia (Nutt.) Fresen.} 



I. xanthifolia Nutt. 



2. Ambrosia L. — Ragweed 

 1. Leaves pinnatifid or bipinnatifid. 



2. Leaves petioled, bipinnatifid; fruit with 5-7 sharp tubercles; plants annual; 

 fields and waste places, common. Aug.-Oct. Common Ragweed [A. 

 artemisiifolia L.} A. elatior L. 



2. Leaves sessile, pinnatifid; fruit with unarmed or with blunt tubercles; 



plants perennial with a slender rhizome; roadsides and waste places, 

 adv. from w. U.S. Western Ragweed. July-Oct. [A. psilostachya sensu 



Gray, non DC.} A. coronopifolia T. dC G. 



L Leaves 3-5-lobed or undivided; plants annual. 



3. Leaves opposite, 3-5-Iobed, 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 base; 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 s. half of 111., extending northw. to Menard Co. 

 A. bidentata Michx. 



3. Xanthium L. — Cocklebur 



1 . Leaves lanceolate, acute at each end, white-canescent beneath, each with a 

 3-parted spine at the base; waste ground, introd. from trop. Am. Aug.- 

 Oct. Spiny Cocklebur X. spinosum L. 



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



2. Body of the fruit and its prickles glandular and more or less hispidulous; 

 waste places, cult, ground, and river banks. Aug.-Oct. [X. italicum of 



auth., not Mor.; X. saccharatum sensu Widder, ex p.} 



X. commune Britt. 



2. Body of fruit and its prickles merely glandular to glandular-puberulent, 

 or nearly glabrous; waste places, fields, and along rivers. Aug.-Oct. [X. 

 canadense of auth., not Mill.; X. pungens Wallr.; X. glabratum Britt.; 

 X. americanum of auth., (?) not Walt.} X. pennsylvaniaim Wallr. 



Tribe 2. Vernonieae 



4. Vernonia Schreb. — Ironweed 



1 . Leaves glabrous beneath or merely puberulent. 



2. Leaves glabrous, linear-lanceolate, punctate beneath; inflorescence dense, 



fastigiate; moist ground, locally throughout 111. July-Aug 



V. fasciculata Michx. 



