GENUS 55. THISTLE FAMILY. 
Leaves 1—2-pinnatifid ; annual weed. 
Leaves crenate-dentate, or somewhat lyrate; perennials. 
Stem glabrous, or pubescent or puberulent above; rootstock 
tuberous-thickened. 
Stem hirsute or villous. 
Stem leaves auricled, clasping at base; rootstock thick. 
Stem leaves sessile, not auricled; rootstock long, slender. 
1. Parthenium Hysteréphorus L. Santa Maria. 
Fig. 4432. 
P. Hysterophorus L. Sp. Pl. 988. 1753. 
Annual, strigose-pubescent or somewhat villous, usu- 
ally much branched, 1°-23° high. Leaves ovate to ob- 
long in outline, I-2-pinnately parted into linear or lan- 
ceolate toothed or pinnatifid segments, thin and flaccid; 
heads numerous, 23’-3” broad; involucre saucer-shaped, 
its bracts concave, the outer ones rhombic, the inner 
broader; ray-flowers few; rays reniform, white, about 
#’ wide; achenes obovate, about 4” long. 
Waste and cultivated grounds, southern Pennsylvania to 
Illinois, Missouri, Florida and Texas. Throughout tropical 
America, July-Sept. 
495 
. P. Hysterophorus. 
. P.integrifolium, 
. P. auriculatum. 
4. P. hispidum, 
2. Parthenium integrifolium L. Amer- 
ican Fever-few. Prairie Dock. 
Fig. 4433. 
P. integrifolium L. Sp. Pl. 988. 1753. 
Stem stout, striate, finely pubescent with 
short hairs, or glabrous below, corymbosely 
branched above, 1°-4° high. Rootstocks tuber- 
ous thickened; leaves firm, ovate or ovate- 
oblong, acute or acuminate, crenate-dentate 
or somewhat lyrate at the base, hispidulous 
and roughish on both sides, the lower and 
basal ones petioled, often 12’ long and 5’ wide, 
the upper smaller, sessile; heads numerous 
in a dense terminal corymb; involucre nearly 
hemispheric, about 3” high, its bracts firm, 
the outer oblong, densely appressed-pubes- 
cent, the inner broader, glabrous, or ciliate 
on the margins; rays white or whitish. 
In dry soil, Maryland to Minnesota, south to 
Georgia, Missouri and Arkansas. Cutting-almond. 
Wild quinine. May-Sept. 
3. Parthenium auriculatum Britton. Auri- 
cled Parthenium. Fig. 4434. 
P. auriculatum Britton, in Britt. & Brown, Ill. Fl. 3: 
521. 1898. 
Rootstock an oval erect tuber twice as long as 
thick ; stem villous-pubescent, 13°-23° high. Leaves 
rough above, villous, especially on the veins be- 
neath, oval, ovate or oblong, irregularly crenate- 
dentate, some or all of them laciniate or pinnatifid 
at the base, the basal and lower slender-petioled 
with petiole as long as the blade, or longer, the 
upper with a sessile clasping auricled base, or 
with margined clasping petioles; inflorescence 
densely corymbose, its branches villous-tomen- 
tose; bracts of the involucre densely canescent. 
Mountains of Virginia. 
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