Genus 3. 



RAGWEED FAMILY 



2. Gaertneria discolor (Nutt.) Kuntze. 

 White-leaved Gaertneria. Fig. 4130. 



Ambrosia tomentosa Nutt. Gen. 2: 186. 181S. Not 

 Gaertneria tomentosa (A. Gray) Kuntze. 



Franseria discolor Nutt. Trans. Am. Phil. Soc. (II.) 

 7: 345- 1841. 



Gaertneria discolor Kuntze, Rev. Gen. PI. 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'-$' long ; 

 sterile racemes narrow, commonly solitary, l'-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. 



On rich prairies 



3. Gaertneria tomentosa (A. Gray) 



Kuntze. Woolly Gaertneria. 



Fig. 4131- 



Franseria tomentosa A. Gray, Mem. Am. Acad. 4 : 80. 

 1849. 



G. tomentosa Kuntze, Rev. Gen. PI. 339. 1891. 



Gaertneria Grayi A. Nelson, Bot. Gaz. 34: 35. 1902. 



Erect from a deep perennial root, usually 

 branched at the base, i -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. 



and along rivers, western Nebraska, Kansas and Colorado. Aug.-Sept. 



4. XANTHIUM [Tourn.] L. Sp. PI. 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 1 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"-s" long. 2. X. speciosum. 



