Genus 54.] 



THISTLE FAMILY. 



Stem minutely pubescent, or glabrous below; rootstocks thickened. 

 Stem pilose-pubescent; rootstocks slender, creeping, forming runners. 



I. Parthenium integrifolium L. American Fever-few. 



(Fig. 3875.) 



Parlhenium iiilegri/oliitm L. Sp. PI. 9SS. 



1753- 



Stem stout, striate, finely pubescent with 

 short hairs, or glabrous below, corymbosely 

 branched above, i°-4° high. Rootstocks 

 tuberous-thickened; leaves firm, ovate or 

 ovate-obloug, 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 and partly clasping; heads numer- 

 ous in a dense terminal corymb; involucre 

 nearly hemispheric, about 3" high, its 

 bracts firm, the outer oblong, densely ap- 

 pressed-pubescent, the inner broader, gla- 

 brous, or ciliate on the margins; rays 

 white or whitish. 



In dry soil, Maryland to Minnesota, south 

 to Georgia, Jlissouri and Texas. Called also 

 Cutting .\lmond. May-Sept. 



411 



1. P. integri/olitim. 



2. P. repens. 



Prairie Dock. 



, Parthenium repens Eggert. Creep- 

 ing or Hairy Parthenium. 

 (Fig. 3876.) 



Parlhenium repens Eggert, Cat. PI. St. Louis, 16. 

 1891. 



Similar to the preceding species, but lower, 

 seldom over 2° high. Rootstocks slender, 

 forming runners; stem pilose or hispid with 

 spreading hairs; leaves hispid on both sides, 

 irregularly crenate, sometimes lyrate at the 

 base, the teeth rounded and obtuse; heads 

 fewer, slightly larger, in a smaller looser 

 corymb; outer bracts of the involucre propor- 

 tionately broader. 



Missouri. April-July. 



55. CRASSINA Scepin, Sched. Acido Veg. 42. 1758. 

 [Zinnia L. Syst. Ed. 10, 1221. 1759.] 



.\nnual or perennial herbs, some species shrubby, with opposite entire, or sparingly ser- 

 rate, mostly narrow and sessile leaves, and large or middle-sized heads of both tubular and 

 radiate flowers. Ray-flowers pistillate, yellow, or variegated, persistent on the achene. 

 Disk-flowers perfect, fertile; corolla cyliudraceous, its lobes villous. Involucre campanulate 

 to nearly cylindric, its bracts obtuse, dry, firm, appressed, imbricated in 3 series or more, 

 the outer gradually shorter. Receptacle conic or cylindric, chaffy, the chaff subtending and 

 enwrapping the disk-flowers. .Style branches elongated, not appendaged. Achenes of the 

 ra\--flowers somewhat 3-angled, those of the disk flattened. Pappus of few awns or teeth. 

 [In honor of Paul Crassus, an Italian botanist of the i6th century.] 



.\bout 12 species, natives of the United States and Mexico. 



