AMBBOSIACEAE. 313 



(Br.), Cape May (Li.)- Atlantic— Egg Harbor, May's Laiidiug (C.)- 

 Ocean— Manchester (C.)« 



Family 4. AMBROSIACEAE Reichenb. Rag-weed Family. 



Staminate and pistillate flowers in the same heads; involucre of a few- 

 rounded bracts. 1. Iva. 

 Staminate and pistillate flowers in separate heads, the staminate mostly 

 uppermost; involucre of the pistillate heads bur-like or nut-like. 

 Involucral bracts of the staminate heads united. 2. Ambrosia. 

 Involucral bracts of the staminate heads separate; involucre of pistil- 

 late an oblong bur. 3. Xanthium. 



1. IVA L. 

 1. Iva frutescens L. Marsh Elder, Highwater-shrub . M. p. 909. Salt 

 marshes. Summer. 



2. AMBROSIA L. Ragweed. 



Leaves opposite, palmately 3-5-lobed or undivided; receptacle naked. 



1. A. trifida. 

 Leaves opposite and alternate, 1-2-pinnatifid; receptacle chaffy. 



2. A. art emisae folia. 



1. Ambrosia trifida L. Great Ragweed. M. p. 910. Moist soil. Summer 



and fall, 

 la. Ambrosia trifida integripolia (Muhl.) T. & G. M. p. 910. Moist soiL 

 Summer and fall. 



2, Ambrosia artemisaefolia L. Rag-weed, Hog-weed. M. p. 910. Culti- 



vated fields and waste places. Summer and fall. 



3. XANTHIUM L. Clotbur. BtiRWEEu. (Jocklebur. 

 Leaves lanceolate, not cordate; axils bearing 3-divided spines. 



1. X. spinosum. 

 Leaves orbicular or broadly ovate, cordate, or truncate; axils not spiny. 



Bur 12-20 mm. long, usually nearly glabrous; beaks straight or nearly so. 



2. X. glabratum. 

 Bur 5-30 mm. long; beaks hooked or incurved. 



Body of the bur oblong, twice as long as thick or more. 



Bur and its spines merely puberulent and glandular or with a 

 few hispid hairs. 

 Prickles very dense, slender; leaves thin, sharp-toothed. 



3. X. Permsylvanicum. 

 Prickles scattered, stout; leaves firm, bluntly-toothed. 



4. X. Canadense. 

 Bur or its prickles very hispid. 5. X. commune. 



Body of the bur oval to ovoid, not twice as long as thick. 



6. X. echinatum. 



1, Xanthium spinosum L. M. p. 912. Waste places. Autumn. 



Philadelphia— FhWaxMiihia, Mart. (B. C), Schuylkill above Manayunk 

 (He.), Angora (Ws.). BmcA's— Opposite Trenton, Moyer; near Bristol, 

 Mart. (Fr.). Delaware— lUmcwm Twp. (Fr.), Valley of Darby Creek 

 (B. Sm.), Concord (W. Tr.). Chester— {V.). Lancaster— York Fumaco, 

 Northampton — (P.). 



Camden— Frequent in towns and villages. 



New Castle— City streets and gutters, Wilmington, New Castle, etc. 



