Genus 55. 



THISTLE FAMILY. 



465 



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. 



i. Parthenium Hysterophorus L. Santa Maria. 

 Fig- 443 2 - 



P. Hysterophorus L. Sp. PI. 988. 1753. 



Annual, strigose-pubescent or somewhat villous, usu- 

 ally much branched, i-2* high. Leaves ovate to ob- 

 long in outline, 1-2-pinnately parted into linear or lan- 

 ceolate toothed or pinnatifid segments, thin and flaccid; 

 heads numerous, 2V-3" broad; involucre saucer-shaped, 

 its bracts concave, the outer ones rhombic, the inner 

 broader; ray-flowers few; rays reniform, white, about 

 i" wide ; achenes obovate, about 1" long. 



Waste and cultivated grounds, southern Pennsylvania to 

 Illinois, Missouri, Florida and Texas. Throughout tropical 

 America. July-Sept. 



1. P. Hysterophorus. 



2. P. integrifolium. 



3. P. auriculatum. 



4. P. hispidum. 



2. Parthenium integrifolium L. Amer- 

 ican Fever-few. Prairie Dock. 

 Fig. 4433- 



P. integrifolium L. Sp. PI. 988. 1753. 



Stem stout, striate, finely pubescent with 

 short hairs, or glabrous below, corymbosely 

 branched above, l-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, 111. Fl. 3: 

 521. 1898. 



Rootstock an oval erect tuber twice as long as 

 thick; stem villous-pubescent, iA-24 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. 



3 



