WOOTON AND STANDLEY—FLORA OF NEW MEXICO. 635 
2a. Xanthium commune wootoni Cockerell, Proc. Biol. Soc. Washington 16: 9. 
1903. 
Type Locauity: ‘‘At Espafiola, N. M., and Las Vegas, N. M.” 
Rance: New Mexico. 
New Mexico: Las Vegas; Albuquerque. Valleys and cultivated fields, in the 
Lower and Upper Sonoran zones. 
This seems distinct enough from X. commune to be regarded as a species. It 
certainly is more easily separable from that than are most of the eastern species from 
each other. Professor Cockerell states, however, that he has found both forms of 
fruit on the same plant, hence we hesitate to raise the subspecies to specific rank, 
The occurrence of both forms of fruit on a single plant would not necessarily invalidate 
either as a species but would rather seem to be a result of hybridization. Ordinarily 
the two plants are distinct enough. 
5. AMBROSIA TL. Raaweep. 
Coarse annual or perennial herbs with lobed or dissected, opposite or alternate 
leaves and small inconspicuous flowers; sterile heads racemose, bractless; fertile 
flowers mostly glomerate in the lower axils; involucre of staminate flowers hemi- 
spheric to turbinate, 5 to 12-lobed or truncate; receptacle flat, with filiform chaff 
among the outer flowers; involucre of the solitary pistillate flower nutlike, beaked 
at the apex, usually with 4 to 8 tubercles or stout spines in a row below the beak. 
KEY TO THE SPECIES, 
Leaves mostly 3 or 5-cleft; involucre of staminate heads 3 or 
4-ribbed.... 02... cece ee eee ee eee eee eee eens 1. A. aptera. 
Leaves once to thrice pinnatifid; involucre of staminate flowers 
not ribbed. 
Annual; fruit with sharp tubercles; leaves mostly twice 
parted..................22622- wee e cece eee eee eeeeeee 2. A. artemisiaefolia. 
Perennial; fruit with blunt tubercles or unarmed; leaves 
mostly once pinnatifid..................-...-------- 3. A. psilostachya., 
1. Ambrosia aptera DC. Prodr. 5: 527. 1836. GREAT RAGWEED. 
Ambrosia trifida terana Scheele, Linnaea 22: 156. 1849. 
Type LocaLity: Near San Antonio, Texas. 
RanaeE: Texas to southern Arizona, 
New Mexico: Vermejo Peak; Mangas Springs; Brockmans Ranch; Cliff; Crains 
Ranch. Wet ground. 
2. Ambrosia artemisiaefolia L. Sp. Pl. 987. 1753. COMMON RAGWEED. _ 
Tyrer Locatity: ‘Habitat in Virginia, Pennsylvania.”’ , 
RanGeE: British America to Mexico and South America. 
New Mexico: Santa Fe; Ogle; Agricultural College. Waste ground. 
The common ragweed of the Eastern States is, so far, a rare introduction into New 
Mexico. 
3. Ambrosia psilostachya DC. Prodr. 5: 526. 1836. WESTERN RAGWEED. 
Type Locauity: ‘‘In Mexico inter San-Fernando et Matamoros.”’ 
Ranae: Illinois and Saskatchewan to Arizona and California, south into Mexico. 
New Mexico: Chama; Shiprock; Pecos; Santa Fe; Clayton; Nara Visa; Malaga; 
Albuquerque; Brockmans Ranch; Kingston; Dog Spring; Mesilla Valley. Plains, 
in the Sonoran and Transition zones. 
