209 
6. I. asperifolia L. Low, 1.5 to 3 dm. high: leaves narrowly lanccolate, narrowed 
towards the base, strigose, very entire: heads small, spicate, exceeded by the brac- 
teal leaves: involucre gamophyllous, obpyramidal, 3-angled, 3-toothed.—A Mexican 
species, extending from the vicinity of Vera Cruz to Galveston (J. EF. Bodin). 
48. HYMENOCLEA Torr. & Gray. 
Low and much-branched shrubby minutely canescent or glabrous 
plants, with slender diffuse branches bearing profuse scattered or glom- 
erate paniculate small heads (the two sexes intermixed or the female 
in lower axils), alternate and linear-filiform leaves (the lower sparingly 
and irregularly pinnately parted), sterile involucre gamophyllous and 
saucer-Shaped, involucre to the solitary fertile flower ovoid or fusiform 
(beaked at apex and the lower part furnished with 9 to 12 dilated and 
silvery-scarious persistent transverse wings), turgid achenes, and no 
pappus. 
1. H. monogyra Torr. & Gray. Fructiferous involucre 4 mm. long, winged only 
at the middle by a whorl of obovate or rhombic-reniform radiating scales.—West of 
the Pecos. 
49. AMBROSIA Tourn. (RAGWEED), 
Coarse homely weeds, with opposite or alternate lobed or dissected 
leaves, inconspicuous greenish flowers, sterile and fertile flowers in 
different heads on the same plant, the fertile 1 to 3 together and sessile 
in the axil of leaves or bracts at the base of the racemes or spikes of 
sterile heads, sterile involucres flattish or top-shaped (of 7 to 12 bracts 
united into a cup), almost separate anthers, fertile involucre (fruit) ob- 
long or top-shaped (closed, pointed, resembling an achene and usually 
with 4 to 8 tubercles or horns near the top in one row) and inclosing a 
single flower consisting of a pistil only, ovoid achenes, and no pappus. 
* Sterile heads sessile in a dense spike, the top-shaped involucre extended on one side into a 
large lanceolate hooded bristly-hairy tooth or appendage: fertile involucre oblong and 
4-angled. 
1. A. bidentata Michx. Hairy, 3 to 9 dm. high, very leafy: leaves alternate, 
lanceolate, partly clasping. nearly entire except a short lobe or tooth on each side 
near the base: fruit with 4 stout spines and a central beak.—Prairies and alluvial 
ground, from the prairie States throughout Texas to Mexico, 
* * Sterile heads in single or panicled racemes or spikes, the involucre regular. 
+. Leaves opposite, ample, palmately cleft: sterile involucre 3-ribbed on one side. 
2. A. trifida L. (GREAT RAGWEED.) Stem stout, 9 to 50 dm. high, rough-hairy, 
as are the large deeply 3-lobed leaves, the lobes oval-lanceolate and serrate; petioles 
margined: fruit obovate, 8 to 10 mm. long, 5 or 6-ribbed, terminating above in 
spinous tubercles around the conical beak.—Moist river banks, throughout eastern 
and central Texas. 
3. A. aptera DC. Like the preceding, but petioles not margined, larger leaves 
commonly 5-lobed (the middle lobe often 3-cleft), sterile racemes more numerous and 
paniculate, fruit smaller (4 to 6 mm. long), 4 to 8-ribbed and with 4 to 6 short or ob- 
solete tubercles.—Low grounds in southern and western Texas. 
