550 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM, 
AMBROSIACEAE. Racweep Famity. 
Heads with both staminate and pistillate flowers; involucre open ......... Iva. 
Heads unisexual; pistillate heads usually spiny. 
Bracts of staminate heads separate; pistillate heads forming an oblong 
bur. ....2. 22222-22222 -222 22-2222 eee eee ee ee ee ----- 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... .. . 1. I. xanthiifolia. 
Heads in axillary racemes; leaves oblong or obovate, mostly entire.... 2. J. axillaris. 
1. Iva xanthiifolia Nutt. Gen. 2: 185. 1814. 
Iva paniculata Nutt. Trans. Am. Phil. Soc. 7: 347. 1840. 
Type Locauity: ‘‘ Near Fort Mandan,”’ North Dakota. 
Rance: Washington to Saskatchewan, south to Utah and New Mexico. 
SPECIMENS EXAMINED: West Klickitat County, Suksdorf 355; Leavenworth, Whited 
1447; Pullman, Piper 1381; Spokane, Areager 532. 
ZONAL DISTRIBUTION: Arid Transition. 
2. Iva axillaris Pursh, F]. 2: 743. 1814. 
Type Locatiry: ‘‘In upper Louisiana.’ Collected by Bradbury. 
RanGeE: 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, Sandberg & Leiberg 
318. 
ZONAL DISTRIBUTION: Upper Sonoran. 
XANTHIUM. Cock_Lesur. 
Leaves lanceolate, not cordate, bright green above, white-tomentose 
beneath, the axils bearing spines..........-.-.....22-2-2--..--- 1. X. spinosum. 
Leaves ovate to orbicular, cordate; axils without spines. 
Body of the burs 2.5 to 3 cm. long; spines about 100, hispid, 
strongly hooked.............-----------------002 2-02 ee ee 2. X. 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. X. oligacanthum. 
Spines 50 to 70. 
Burs oblong or slightly ovate; spines about 50, each two- 
thirds as long as the diameter._.....-.......---.--- 4. X. affine. 
Burs ovate; spines about 70, each one-half as long as 
the diameter....-...........-.-2-2--.------------- 5. X. varians. 
1. Xanthium spinosum L. Sp. Pl. 2: 987. 1753. 
Type Locauity: ‘‘ Habitat in Lusitania.” 
SPECIMENS EXAMINED: Columbia River, Brandegee 889, Colfax, Piper 1591. 
Becoming common as a weed in various parts of eastern Washington; locally known as 
‘Chinese Thistle.’’ 
2. Xanthium speciosum Kearney, Bull. Torr. Club 24: 574. 1897. 
Xanthium silphifolium Greene, Pittonia 4: 60. 1899. 
Type Loca.ity: ‘‘ Near Wolf Creek Station,’ Tennessee. 
