Part 1, 1922 AMBROSIACEAE 15 
4. Hymenoclea monogyra T. & G.; (Torr. in Emory, Notes Mil. Rec. 
143, hyponym. 1848) A. Gray, Mem. Am. Acad. II.4: 79. 1849. 
A shrub 1-4 m. high, with straw-colored or gray bark; branches ascending, puberulent at 
first; leaves filiform, or the lower with filiform divisions 2-5 cm. long, about 9.5 mm. broad, 
puberulent, and somewhat tomentulose beneath, grooved below; heads in small axillary clus- 
ters, the staminate 8—12-flowered, usually mixed with the pistillate ones; involucre turbinate, 
3-4 mm. broad, puberulent; lobes 5 or 6, ovate, indistinctly toothed; paleae of the receptacle 
with linear-spatulate tips; corolla funnelform, membranous, puberulent; lobes triangular; style 
nearly as long as the stamens; stigma erose; pistillate heads subtended by scale-like, ovate, 
erose bractlets; body of the fruit oblanceolate, fusiform, 4-5 mm. long, with a single series of 
7-12 wings above the middle; beak hyaline, 2 mm. long; wings scarious, elliptic, obovate, or 
oblanceolate, acute and erose. 
TyPE LOCALITY: Valley of the Gila [Arizona]. 
DISTRIBUTION: Western Texas and Coahuila to southern California, Lower California, and 
Sinaloa. 
9. AMBROSIA L. Sp. Pl. 987. 1753. 
Hemiambrosia Delpino, Studi Lign. Anem. 57. 1871. 
Annual or perennial coarse herbs, with opposite or alternate, mostly lobed or dissected 
leaves. Staminate heads nodding, racemose or spicate, above the pistillate ones; involucre 
saucer-shaped or rarely turbinate, 5—12-lobed; paleae of the receptacle filiform, often with 
clavate or dilated tips; corolla funnelform, puberulent or glabrous, 5-toothed; filaments mona- 
delphous; anthers distinct, oblong with acuminate or cuspidate incurved tips; pistil abortive; 
style shorter than the stamens; stigma peltate, penicillate. Pistillate heads erect; involucre 
nut-like, obovoid, usually with a single series of tubercles or short erect spines near the apex 
and a truncate, 3—4-toothed beak; pistil solitary, without corolla. 
Type species, Ambrosia maritima I. 
Staminate heads spicate; involucre turbinate, very oblique, produced on the 
side away from the stem into a lanceolate, acuminate lobe. I. CERCOMERIS. 
Staminate heads racemose; involucre slightly if at all oblique, not produced 
into an elongate lobe on either side. II. EUAMBROSIA. 
I. CERCOMERIS 
One species. 1. A. bidentata. 
II. EUAMBROSIA 
Leaves pinnatifid to tripinnatifid. 
Leaves green, at least above. 
Leaves distinctly petioled, mostly bi- or tripinnatifid (except in A. 
longistylis); spines or tubercles sharp; annuals or perennials 
with a branched root. 
Body of fruit 2-2.5 mm. long; beak 1 mm. long or less. 
Stem decidedly hirsute. 
Leaf-segments narrow, linear, acute, ascending. 
Leaf-segments broad, the primary ones spreading, the 
ultimate ones short and obtuse; beak 0.5 mm. long. 3. A. cumanensis. 
Stem strigose, rarely with longer hairs. 
Body of fruit 2—2.5 mm. long; beak nearly 1 mm. long; 
staminate involucre 3-4 mm. broad;ultimate leaf- 
segments broad and obtusish. 4. A. peruviana. 
Body of fruit 2 mm. long; beak not more than 0.5 mm. 
long;staminate involucre not more than 3 mm. 
broad; ultimate leaf-segments lanceolate, acute. 
to 
aN 
. tenutfolia. 
Fruit rugose. 5. A. monophylla. 
Fruit smooth. 6. A. glandulosa. 
Body of fruit 3 mm. long or more; beak more than | mm. long. 
Lower leaves mostly bipinnatifid, with narrow segments; 
staminate heads about 3 mm. broad. 7. A. elatior. 
Lower leaves mostly pinnatifid, with broad segments; stami- 
nate heads 4-5 mm. broad, except in A. Rugeliz. 
Staminate involucre and lower surface of leaves hirsute. 
Lobes of staminate involucre acute; beak of the 
fruit as long as the body; upper leaves entire. 8. A. diversifolia. 
Lobes of staminate involucre rounded; beak of the 
fruit shorter than the body; upper leaves usu- 
ally pinnatifid. 
