GENUS 3. RAGWEED FAMILY. 
2. Gaertneria discolor (Nutt.) Kuntze. 
White-leaved Gaertneria. Fig. 4130. 
Ambrosia tomentosa Nutt. Gen. 2: 186. 1818. Not 
Gaertneria tomentosa (A. Gray) Kuntze. 
Franseria discolor Nutt. Trans. Am. Phil. Soc. (II.) 
7: 345. 1841, 
Gaertneria discolor Kuntze, Rev. Gen. Pl. 339. 1891. 
Erect or ascending from perennial rootstocks, 
branched, about 1° high. Leaves nearly all bipin- 
natifid, petioled, densely white-tomentose beneath, 
green and pubescent or glabrate above, 2’-5’ long; 
sterile racemes narrow, commonly solitary, 1’-2’ | 
long; fruiting involucres clustered in the axils, 
finely canescent, about 3” long, mostly 2-flowered, 
armed with short sharp conic spines. 
In dry soil, South Dakota, Nebraska, Wyoming, 
Kansas, Colorado and New Mexico. Aug.—Sept. 
3. Gaertneria tomentésa (A. Gray) 
Kuntze. Woolly Gaertneria. 
Fig. 4131. 
Pree tomentosa A. Gray, Mem. Am. Acad. 4: 80. 
1849. : 
G. tomentosa Kuntze, Rev. Gen. Pl. 339. 1891. 
Gaertneria Grayi A. Nelson, Bot. Gaz. 34: 35. 1902. 
Erect from a deep perennial root, usually 
branched at the base, 1°-3° high. Leaves pin- 
nately lobed or divided, finely and densely to- 
mentose on both sides, or ashy above, the terminal 
segment lanceolate or oblong-lanceolate, acumi- 
nate, serrulate or entire, very much larger than 
the 2-6 rather distinct narrow lateral ones; sterile 
racemes solitary, 2’-4’ long; fruiting involucres 
solitary, or 2-3 together in the upper axils, ovoid, 
finely canescent or glabrate, 2-flowered, about 3” 
long, armed with subulate-conic, very acute, 
sometimes curved or hooked spines. 
On rich prairies and along rivers, western Nebraska, Kansas and Colorado. Aug.—Sept. 
4. XANTHIUM [Tourn.] L. Sp. Pl. 987. 1753. 
Monoecious annual branching coarse rough or spiny herbs, with alternate lobed or dentate 
leaves, and rather small heads of greenish discoid flowers, the staminate ones capitate- 
clustered at the ends of the branches, the pistillate axillary. Staminate heads with a short 
involucre of I to 3 series of distinct bracts; receptacle cylindric, chaffy; corollas tubular, 
5-toothed; anthers not coherent, mucronate at the apex; filaments monadelphous; style slen- 
der, undivided. Pistillate heads of an ovoid or oblong, closed involucre, covered with hooked 
spines, 1-2-beaked, 2-celled, each cavity containing one obovoid or oblong achene; corolla 
none; pappus none; style 2-cleft, its branches exserted. [Greek, yellow, from its yielding 
a yellow hair-dye.] 
About 15 species, of wide geographic distribution. Type species: Xanthium strumarium L. 
Leaves lanceolate, acute at both ends; axils bearing 3-divided yellow spines. 
1. X. spinosum, 
Leaves orbicular or broadly ovate, cordate to truncate at base; no axillary spines. 
Bur, or its prickles, or both, more or less hispid-pubescent ; beaks incurved. 
Body of the bur ovoid to oval, twice as long as thick or shorter. : 
Bur 1’ long or more, the prickles 4”-5” long. 2, X. speciosum. 
