38 NORTH AMERICAN FLORA [VOLUME 33 
Leaves subobtusely lobed; fruits thicker; prickles 
thicker and more often 3.5—7 mm. long. 12. X. pennsylvanicum. 
Body of the fruit commonly thick-ovoid or subglobose. 
Beaks not elongate (3-4 mm. long);species of the 
® United States. 5. X. globosum. 
Beaks elongate (6-9 mm. long); species of Mexico and 
South America. 15. X. australe. 
Fruits more or less setose, hispid, or pilose. 
Prickles of mature fruits setose or hispid but not truly pilose. 
Fruits 8-12 mm. long; prickles about 2 mm. long. 2. X. strumarium. 
Fruits and prickles longer. 
Prickles not strongly hispid. 
Prickles unequal, certain ones near the beak 
very long (8-10 mm.). ll. X.inflexum. 
Prickles equal or subequal. 
Body cylindric to ovoid, the beaks not con- 
spicuously elongate. 12. X. pennsylvanicum. 
Body globose-ovoid, the beaks elongate. 15. X. australe. 
Prickles strongly hispid. 
Width of body about one-half its length. 16. X. echinatum. 
Width of body even less. 17. X. italicum. 
Prickles of mature fruits densely and softly long-pilose. 18. X. acerosum. 
Mature fruits commonly very large, 2.8-4 cm. long and 2—3 cm. wide, 
including prickles and beaks. 
Prickles commonly arcuate and horn-shaped, rather thickish. 
Prickles commonly few and remote or subremote, the lowest 
ones grooved upon the ventra! face. 19. x. oviforme. 
Prickles more often numerous and closely grouped together, 
terete. 21. XK. campestre. 
Prickles not conspicuously arcuate except at the hooked apex, 
slender. 20. X. speciosum. 
1. Xanthium spinosum L. Sp. Pl. 987. 1753. 
Xanthium xanthocarpon Wallr. Beitr. Bot. 1: 241. 1844. 
Acanthoxanthium spinosum Fourr. Ann. Soc. Linn. Lyon II. 17: 110. 1869. 
Stem pubescent, branched, erect or ascending, 3-12 dm. high; leaves 4-12 cm. long, 
blades lanceolate or ovate-lanceolate, acuminate or acute at both ends, 2—4-lobed or the upper 
ones entire, canescent below and upon the veins above; axils armed with yellow tripartite 
spines 2.5 em. or less in length; fruit oblong-cylindric, commonly yellowish-green, pubescent; 
beaks slender, smooth, sharp, about 3 mm. long, commonly one and sometimes even both 
missing; prickles somewhat apart or even remote, doubly curved above like a swan’s neck 
and ending in a hook which extends backwards about one fourth the length of the prickles. 
TYPE LOCALITY: Portugal. 
DISTRIBUTION: Now generally distributed almost throughout the United States; also in South 
America, where probably native, central Europe, western Asia, southern Africa, and Australia. 
ILLUSTRATIONS: Lam. Tab. Encyce. pl. 765. f. 4; Gaertn. Fruct. pl. 164; Fl. Deuts. ed. 5. pl. 
3000; E. & P. Nat. Pfl. 45: f. 71 N; Rob. & Fern. Man. f. 985; Britt. & Brown, Ill. Fl. f. 3598; ed. 
2. f. 4132; Field Mus. Publ. Bot. 4: pl. 7. f. 1; pl. 8, f. 1-3. 
2. Xanthium strumarium L. Sp. Pl. 987. 1753. 
Xanthium priscorum Wallr. Beitr. Bot. 1: 227. 1844. 
Xanthium antiquorum Wallr. Beitr. Bot. 1: 229. 1844. 
Xanthium abyssinicum Wallr. Beitr. Bot. 1: 230. 1844. 
Xanthium discolor Wallr. Beitr. Bot. 1: 232. 1844. 
Xanthium Roxburghii Wallr. Beitr. Bot. 1: 233. 1844. 
Xanthium brevirostre Wallr. Beitr. Bot. 1: 235. 1844. 
Xanthium strumarium antiquorum Ball, Jour. Linn. Soc. 16: 503. 1878. 
Stem somewhat branched, pubescent, 0.4-1.5 m. high; leaves 0.6—2.5 dm. long, the petioles 
equaling or exceeding the blades; blades triangulate-deltoid, truncate or subcordate at the 
base, 3—5-lobed, on both sides similarly colored and clothed with appressed strigose hairs; 
body of the fruit ovoid, or swollen and subglobose, commonly greenish, pubescent, 0.8-1.4 
cm. long; beaks straight or incurved at the apex, 1-2 mm. long, often standing apart; prickles 
straight, hooked at the apex, glabrous above, more or less pubescent below, about 2 (rarely 
3) mm. long. 
TYPE LOCALITY: Europe. 
DISTRIBUTION: Adventive in Massachusetts and California; native of north-temperate and 
tropical regions of the Eastern Hemisphere. 
ILLUSTRATIONS: Gaertn. Fruct. pl. 164; Wight, Ic. Pl. Ind. Or. pl. 1104; Fl. Deuts. pl. 2999; 
Field Mus. Publ. Bot. 4: pl. 7, f. 2; pl. 8, 4-8. 
