ParT 1, 1922] AMBROSIACEAE 43 
5-7 mm. long; prickles commonly numerous and slender (rarely either subremote or rather 
thick), hispid from the base up to the middle, glabrous above, hooked at the apex, 3-7 mm. 
long. 
TYPE LOCALITY: Italy. 
DISTRIBUTION: Quebec to West Virginia, Saskatchewan, Washington, and California; Oaxaca; 
also in Europe. 
ILLUSTRATIONS: Reichenb. Ic. Crit. pl. 323; Rob. & Fern. Man. f. 987; Britt. & Brown, IIl. 
Fl. ed. 2. f. 4135, 4138; Field Mus. Publ. Bot. 4: pl. 7, f. 17; pl. 9, f. 25-30. 
18. Xanthium acerosum Greene, Pittonia 4: 63. 1899. 
Stem flexuous, often lengthwise-punctate with linear purple dots, scabrous above, almost 
glabrous below, probably about 4—9 dm. high; leaves 0.7—2 dm. long including the petioles; 
petioles and blades about equal; blades broadly subcordate-ovate, obtuse, crenate-dentate, sca- 
brous; body of the fruit cylindric, moderately glandular-pubescent, 1.5-1.9 cm. long and 6-7 
mm. thick; beaks slender, attenuate, softly pubescent, nearly straight or irregularly incurved, 
very slightly hooked at the apex, 7-8 mm. long; prickles subremote, hardly numerous, delicate, 
closely covered almost up to the apex with soft and rather long hairs, straight or nearly so, at 
times half of them bearing apical hooks, again scarcely a single prickle hooked at the apex, 
commonly 6-9 mm. long. 
TYPE LOCALITY: Near Fargo, North Dakota. 
DISTRIBUTION: New York (where apparently adventive), Wiscon in, North Dakota, and 
Nebraska. 
ILLUSTRATIONS: Field Mus. Publ. Bot. 4: pl. 7, f. 18; pl. 9, f. 22-24. 
19. Xanthium oviforme Wallr. Beitr. Bot. 1: 240. 1844. 
Xanthium canadense Hook. Fl. Bor. Am. 1: 308. 1833. Not X. canadense Mill. 1768. 
Xanthium silphiifolium Greene, Pittonia 4: 60. 1899. 
Stem little branched, smooth below, somewhat scabrous above, 3-7 dm. high; leaves 
0.7-2 dm. long including the petioles; peticles and blades about equal; sida thin, not clearly 
lobed, deltoid-ovate, sometimes scarcely 3-nerved, unequally sinuate-dentate, uniform in 
color and scabrous on both sides, either rounded or truncate or cordate at base; fruits rather 
few, commonly arranged singly, finally becoming very large; bodies oblong-ovate, glandular- 
hispid or rarely somewhat glabrate, when mature about 2 cm. long and 1.2 cm. thick; beaks 
strong, thick, hispid, incurved above, strongly hooked at the apex, about 8 mm. long; prickles 
remote or subremote (or sometimes almost crowded together), strong, arcuate and horn- 
shaped, ferrugineous-hispid (at least upon the back and sides) almost up to the strongly hooked 
apex, the lower ones commonly grooved upon the ventral surface, (5—) 7-10 mm. long. 
TYPE LOCALITY: Sandy island and banks of the Columbia River (vide Millsp. & Sherff, Field 
Mus. Publ. Bot. 4: 47, footnote 1. 1919). 
DISTRIBUTION: Washington and probably Oregon; adventive, formerly at least, in southwestern 
Tllinois. 
ILLUSTRATIONS: Field Mus. Publ. Bot. 4: pl. 7, f. 19; pl. 10, f. 1-3. 
20. Xanthium speciosum Kearney, Bull. Torrey Club 24: 574 
1897. 
Xanthium bubalocarpon Bush, Rep. Missouri Bot. Gard. 17: 123. 1906. 
Stem erect, robust, branched, at the base finally 2.5 cm. thick, more or less (below obtusely 
and above acutely) quadrangulate, papillose-scabrous especially above, the upper part purple- 
punctate with small linear spots, 1-1.5 m. high; leaves 1—3.5 dm. long including the petioles; 
petioles almost equaling the blades; blades broadly triangular-ovate, obtusely and shallowly 
3-5-lobed, dentate, thickish, cordate at the base, scabrous (often with small papillae) on both 
sides; fruits very large, ovoid er conic; bodies ovate-cylindric, scarcely visible among the 
numerous prickles, glandular-pubescent, finally about 2-2.3 mm. long and 7-8 mm. thick; 
beaks attentuate, hispid, incurved or almost straight, hooked at the apex, 6-11 mm. long; 
prickles crowded, rather slender, the lower half or two thirds hispid, smooth toward the hooked 
apex, commonly 7-9 mm. long; entire fruit (prickles and beaks included) finally 3-4 cm. long 
and 2-2.5 (-3) cm. wide. 
