550 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



AMBROSIACEAE. Ragweed Family. 



Heads with both staininate and pistillate flow-ers; involucre open Iva. 



Heads unisexual: pistillate heads usually spiny. 



Bracts of staniinate heads separate; pistillate heads forming an oblong 



bur Xanthium. 



Bracts of staminate heads united. 



Pistillate flowers solitary in each head; spines in a single series Ambrosia. 



Pistillate flowers 1 to 4 in each head; spines in several series Gaertneria. 



IVA. 



Heads in dense panicles; leaves ovate or orbicular, coarsely serrate I. /. .ranthiifolia. 



Heads in axillary racemes; leaves oblong or obovate, mostly entire 2. /. axillaris. 



1. Iva xanthiifolia Nutt. Gen. 2: 185. 1814. 



Iva paniculata Nutt. Trans. Am. Phil. Soc. 7: 347. l«4u. 

 Type locality: "Near Fort Mandan," North Dakota. 

 Range: Washington to Saskatchewan, south to Utah and New Mexico. 

 Specimens examined: West Klickitat County, Suhsdorf 355; Leavenworth, Whited 

 1447; Pullman, Piper 1381; Spokane, Kreager 532. 

 Zonal distribution: Arid Transition. 



2. Iva axillaris Pursh, Fl. 2: 743. 1814. 



Type locality: "In upper Louisiana." Collected by Bradbury. 



Range: British Columbia to Saskatchewan, south to California and New Mexico. 



Specimens examined: Wenache, Whited 1133; Morgans Ferry, Suksdorf 450; Wash- 

 tucna, Elmer 1038; Coulee City, Henderson, July 11, 1892; Lake <& Hull, August 7, 1897; 

 Wilson Creek, Lake & Hull 739; Junction, Crab, and Wilson creeks, Sandberrj & Leiberg 

 318. 



Zonal distribution: Uj^per Sonoran. 



XANTHIUM. Cocklebur. 



Leaves lanceolate, not cordate, bright green above, white-tomentose 



beneath, the axils bearing spines 1. A'. spi7iosum. 



Leaves ovate to orbicular, cordate; axils without spines. 



Body of the burs 2.5 to 3 cm. long; spines about 1(X), hispid, 



.strongly hooked 2. A^. speciosum. 



Body of the burs 1.5 to 2 cm. long. 



Spines about 20, approximately as long as the body of the 



narrowly oblong bur 3. A'. oUgacanthum. 



Spines 50 to 70. 



Burs oblong or slightly ovate; spines about 50, each two- 

 thirds as long as the diameter 4. A. affine. 



Burs ovate; spines about 70, each one-half as long as 



the diameter 5. A. varians. 



1. Xanthium spinosum L. Sp. PI. 2: 987. 1753. 

 Type locality: " Habitat in Lusitania." 



Specimens examined: Columbia River, 5raft<7ff/ec 889, Colfax, Pi/w 1591. 

 Becoming common as a weed in various parts of eastern Washington; locally knov^n as 

 "Chinese Thistle." 



2. Xanthium speciosum Kearney, Bull. Toir. Ciiil) 24: 574. 1897. 

 Xanthium silphiifolium Greene, Pittonia 4; GO. 1899. 



Type locality: " Near Wolf Creek Station," Tennes.see. 



