342 AMBROSIACEAE. Vor. III. 
4. Ambrosia psilostachya DC. Western Rag- 
weed. Fig. 4128. 
Ambrosia psilostachya DC. Prodr. 5: 526. 1836. 
Similar to the preceding species, but perennial by 
long rootstocks, the leaves thick, the pubescence stri- 
gose or hispid. Stems usually much branched, 2°-6° 
high, rather stout; leaves 1-2-pinnatifid, 2’-5’ long, 
the lobes acutish; racemes of sterile heads several or 
numerous, 2’-6’ long, the involucres campanulate, the 
receptacles chaffy; fertile heads mostly solitary, ovoid 
or obovoid, reticulated, short-pointed, unarmed, or 
with about 4 short tubercles, pubescent, 14’”-2” long. 
In moist open soil, Illinois to Saskatchewan, Texas, 
Mexico and California. July—Oct. 
3. GAERTNERIA Med. Act. Pal. 3: 244. 
1785. Phil. Bot. 45. 1789. 
[FRANSERIA Cav. Icon. 2: 78. pl. 200. 1793.] 
Hispid or tomentose branching herbs, with the aspect of Ambrosias, sometimes woody at 
the base, with mostly alternate lobed or divided leaves, and small monoecious greenish heads 
of discoidal flowers, the staminate in terminal spikes or racemes, the pistillate solitary or 
clustered in the upper axils. Involucre of the pistillate heads ovoid or globose, closed, 
1-4-celled, 1-4-beaked, armed with several rows of spines and forming a bur in fruit; corolla 
none or rudimentary; style deeply bifid, its branches exserted; stamens none; achenes obo- 
void, thick, solitary in the cells; pappus none. Staminate heads sessile, or short-peduncled, 
their involucres broadly hemispheric, open, 5-12-lobed; receptacle chaffy; corolla regular, the 
tube short, the limb 5-lobed; style undivided; anthers scarcely coherent; mucronate-tipped. 
[In honor of Joseph Gaertner, 1732-1791, German botanist. ] 
About 25 species, natives of America. In addition to the following, some 12 others occur in the 
western and southwestern United States. Type species: Xanthium fruticosum L. f. 
Plant hirsute; annual; spines of the fruiting involucre long, flat. ; 1. G. acanthicarpa. 
Leaves densely white-tomentose beneath; spines short, conic; perennials. 
Leaves bipinnatifid. 2. G. discolor. 
Leaves pinnately divided, the terminal segment large. 3. G. tomentosa. 
1. Gaertneria acanthicarpa ( Hook.) 
Britton. Hooker’s Gaertneria. 
Fig. 4129. 
Ambrosia acanthicarpa Hook. Fl. Bor. Am. 1: 309. 
1833. 
Franseria Hookeriana Nutt. Trans. Am. Phil. Soc. ~\3a 
CII.) 7: 345. 1841. ep 2} G) 
Gaertneria acanthicarpa Britton, Mem. Torr. Club w(t @ 
5: 332. 1894. w e) GC 
Franseria acanthicarpa Coville, Contr. Nat. Herb. \ by) ¢ ry ial 
4: 129. 1893. : Oho 
Annual, erect or diffuse, paniculately branched, 
1°-2° high; stem hirsute or hispid. Lower and 
basal leaves slender-petioled, bipinnatifid, 2’-4’ 
long, the upper short-petioled or sessile, once- 
pinnatifid, or merely lobed; racemes of sterile 
heads usually numerous, 1-3’ long; fruiting 
involucres clustered in the axils, 3-4” long, 
commonly 1-flowered, armed with numerous 
long flat straight spines. 
In moist soil, Saskatchewan to western Ne- 
braska and Texas, west to British Columbia and 
California. Sand-bur. Recorded from Minnesota. July—Sept. 
_ Gaertneria tenuifélia (A. Gray) Kuntze, a southwestern perennial species with pinnately 
esected leaves, the fruiting involucre only about 1” long, is recorded as extending eastward into 
ansas, 
