Par? 1, 1922] AMBROSIACEAE 9 
1. Chorisiva nevadensis (M. E. Jones) Rydberg. 
Iva nevadensis M. E. Jones, Am. Nat. 17: 973. 1883. 
A low diffusely branched annual, with a stout tap-root; stems 1-2 dm. high, hirsutulous; 
leaves obovate in outline, pinnately 3—7-parted, 1-2 cm. long, cinereous-hispidulous; lobes 
ovate or obovate, obtuse; involucre hemispheric, about 2 mm. broad; bracts 3, hispidulous- 
canescent, ovate with oblong obtuse foliaceous tips; staminate flowers 8—10; corolla villous, fun- 
nelform; pistillate flowers usually 3; corolla-tube truncate, villous; achenes 2 mm. long, ob- 
ovate. 
TYPE LOCALITY: Hawthorn, Nevada. 
DISTRIBUTION: Deserts, Nevada. 
5. CYCLACHAENA Fresen. Ind. Sem. Hort. Frankf. 4. 
1836.—Linnaea 12: Litt.-ber. 78. 1838. 
Iva § Picrotus Nutt. Trans. Am. Phil. Soc. II. 7: 347. 1840. 
Annuals, with opposite and alternate leaves. Heads numerous in panicles, ebracteate. 
Involucre turbinate or hemispheric; bracts 5, distinct. Receptacle chaffy; paleae subtending 
the pistillate flower broad, hyaline, nearly as large as the involucral bracts, very concave and 
partly embracing the achenes; those subtending the staminate flowers filiform or nearly so. 
Staminate flowers 8—20; corolla hyaline, funnelform, 5-nerved, 5-toothed: filaments monadel- 
phous; anthers oblong, with acute incurved tips; style thick; stigma peltate, fimbriate. Pis- 
tillate flowers about 5, marginal; corolla wenting or represented by a mete ring. Achenes 
cuneate or obovate, only slightly compressed dorsiventrally. 
Type species, Iva xanthifolia Nutt. 
Leaves canescent beneath, merely toothed. 
Heads sessile or subsessile. 1 
Heads on individual peduncles 4-12 mm. long. Z 
Leaves green, pinnately lobed to pinnatifid; heads peduncled. 
Leaves twice pinnatifid. 3. C. ambrosiacfolia. 
Leaves pinnately 5-lobed. 4. C. lobata. 
. C. xanthifolia. 
. C. pedicellata. 
1. Cyclachaena xanthifolia (Nutt.) Fresen. Ind. Sem. Hort. Frankf. 
4. 1836.—DC. Prodr. 7: 288, as synonym. 1838. 
Iva xanthifolia Nutt. Gen. 2: 185. 1818. 
Iva paniculata Nutt. Trans. Am. Phil. Soc. II. 7: 347. 1840. 
Euphrosyne xanthifolia A. Gray, Pl. Wright..2: 85. 1853. 
A tall and coarse annual; stem 0.5—2 m. high, glabrous or nearly so up to the inflorescence, 
terete; leaves mainly opposite, petioled; petioles 5-15 cm. long; blades ovate or subcordate, 
7-15 cm. long, more or less distinctly triple-ribbed, acuminate, coarsely serrate or incised, 
scabrous above, more or less densely strigose, grayish or sometimes whitish beneath; heads num- 
erous in axillary spikes or panicles and terminal naked panicles, sessile onthe hirsute branches; 
involucre turbinate, 4-5 mm. broad; bracts 5, obovate, acuminate, erose-dentate, hyaline on 
the margin, hispid on the back; paleae of the receptacle hyaline, those subtending the pistil- 
late flowers obovate, very concave, and somewhat hooded, as large as or larger than the in- 
volucral bracts sometimes longer than the achenes; those subtending the staminate flowers 
small, subulate or filiform, usually wanting towards the center; staminate flowers 8-20; corolla 
elongate-obconic, 5-nerved; anthers with incurved acute tips; style thick; stigma peltate, 
fimbriate; pistillate flowers 5; corolla wanting; achenes obovate in outline, somewhat lentic- 
ular, finely muriculate, the tubercles in distinct rows, brown or almost black, 3 mm. long. 
I. xanthifolia represents the northern smaller form, with the axillary flower-clusters in 
simple spikes of larger heads; J. paniculata the common form with more branched inflorescence 
and smaller heads. 
TYPE LOCALITY: Near Fort Mandan [North Dakota]. 
DISTRIBUTION: Alluvial soil from Wisconsin to Saskatchewan, Idaho, New Mexico, Texas, 
and Missouri; rarely introduced in the East, from Maine to Delaware. 
ILLUSTRATIONS: Britt. & Brown, Ill. Fl. f. 3590; ed. 2. f. 4124; Clark & Fletcher, Farm Weeds 
Can. pl. 55. f. 55; ed. 2. pl. 75, f. 76; Clark & Fletcher, Mauv. Herbes Can. pli 35; f.005 Bulle Agr- 
Coll. Colo. 23. pl. 7. 
