Flora of the Palouse Region 183 



lanceolate, acute, entire or toothed: staminate heads short-peduncled, in 

 strict racemes: pistillate heads solitary in the axils: fruit obovoid or oblong, 

 3 mm. long, short-pointed, rough-reticulated, unarmed or with a few short 

 teeth. Introduced at Pullman. 



304. XANTHIUM. 



Annual herbs: leaves alternate, petioled: heads monoecious, in 

 axillary or terminal clusters or short interrupted spikes: the pistil- 

 late 2-flo\vered and below the several- flowered staminate: involu- 

 cre of staminate flowers of several distinct narrow scales: involu- 

 cre of pistillate flowers bur-like, ovoid or oblong, closed, indurated, 

 2-celled, 2-flowered, armed all over with strongly hook-tipped 

 bristles: pappus none: corolla none: akenes obovoid, thick. 



Leaves white beneath, a 3-pointed spine in each axil. X. spixosum. 

 Leaves green on both sides: no axillary spines. X. silphiifouum. 



X. spinosum L. Much branched, the stems decumbent or ascending, 

 pubescent, 30-60 cm. high: leaves ovate-lanceolate, acute or acuminate, en- 

 tire or 3-lobed, cuneate at base, sessile or nearly so, white-tomentose be- 

 neath, green and shiny above, 5-12 cm. long; axils bearing stout 2-3-parted 

 yellow spines: fertile involucre oblong-cylindric, solitary or 2-3 in the upper 

 axils, 1-1.5 cm. long, armed with slender rather weak prickles and beaked 

 with 1 or 2 stouter ones. Sparingly introduced. 



X. silphiifolium Greene. Coarse and stout, 15-90 cm. high, scabrous 

 throughout: leaves broadly ovate, coarsely toothed or somewhat angularly 

 lobed, cuneate at base, 5-10 cm. long, on stout, usually longer petioles: fer- 

 tile involucres about 4 cm. long, armed with numerous hooked spines, the 

 two terminal ones stoutest, all of them glandular-hisdid, except at their apexes, 

 and about 1 cm. long. Common along Snake River. This plant has here- 

 tofore been referred to X. canadense Mill, but no eastern American plant 

 quite matches it. 



305. GRIXDELIA. 



Biennial or perennial herbs: leaves sessile or partly clasping: 

 heads yellow, medium or rather large, solitary, terminating leafy 

 brauches, or occasionally more or less corymbose, many-flowered: 

 rays fertile, numerous, narrow, or rarely none: involucral-scales 

 numerous, narrow: receptacle flat or convex: pappus of 2-8 rigid 

 and early-deciduous awns: style-branches tipped with an append- 

 age: akenes compressed or turgid or the outermost somewhat 3- 

 angled. 



G. nana Nutt. Stemserect, 15-60 cm. high, simple or branched above: 

 basal leaves spatulate. petioled, tlie upper sessile and partly clasping, entire 

 or serrate, glabrous: heads hemispherical, 10-14 mm. broad; bracts with 

 slender revolute tips, sticky-viscid: rays 16-30, 5-8 cm. long: akenes narrow, 

 somewhat 2-toothed at summit: pappus awns 2-3. Infrequent within our 

 limits. 



