AMBROSIACEAE 587 



9. L. Canbyi A. Gray. In swamps: N. J. to S. Car. 



Frequent throughout the pine-barrens of New Jersey; unknown 

 elsewhere. 



AMBROSIACEAE 



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



rounded bracts. I, 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 the 



pistillate heads an oblong bur. 3. Xanthium. 



i. Iva L. 



1. I. frutescens L. Along salt marshes and on muddy seashores: 



N. H. to Fla. and Tex. 



Throughout the tidal marshes and up the Hudson River to 

 Hastings, N. Y. 



Iva xantkiifolia (Fresen.) Nutt. has been reported from the coast of Connecticut as 

 a waif. I have seen only a single specimen from near Bridgeport. 



2. Ambrosia [Tourn.] L. 



Leaves opposite, palmately lobed or undivided. I. A. irifida. 



Leaves opposite and alternate, 1-2 pinnatifid. 2. A. elatior. 



i. A. trifida L. In moist soil: Que. to Fla., the N. W. Terr., 

 Neb., Colo, and Ark. 



Common everywhere except the pine-barrens, always as a 

 weed. The entire-leaved form integrifolia, is not uncommon with 

 the type. 



2. A. elatior L. (A. artemisiaejolia L.). In dry soil: N. S. to Fla., 



west to B. Col. and Mex. Also in the W. I. and S. Am. 



Introduced into Europe as a weed. 



A common and pernicious weed throughout our area. 



Ambrosia bidentata Michx. has been collected in Conn.; scarcely persistent. A. 

 psiloslachya DC. has been recorded as a waif. 



3. Xanthium [Tourn.] L. 



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, amencanum. 



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



