THISTLE FAMILY 937 



Involucre cleft below the middle; throat of the disk-flowers cylindraceous, 



longer than the lobes. 5. T. subnudum. 



Heads discoid; perennials, with a rootstock or woody caudex. 



Plant less than 2 dm. high; involucre with very broad scarious margins. 



6. T. marginatum. 

 Plants 3-6 dm. high; involucre with very narrow scarious margins. 7. T. gracile. 



1. T. trifidum (Poir.) Britton. A slender annual or biennial; stem branched. 

 3-9 dm. high, leafy; leaves bipinnately divided; inner bracts united not higher 

 than the middle, with broad scarious margins; ligules 12-15 mm. long; awns of 

 the pappus rather short, not longer than the width of the achenes. In dry soil: 

 Neb. Tex. N.M. e Colo. Plain Submont. Je-Au. 



2. T. tenue Rydb. Stem 1-3, slender, less than 2 mm. in diameter, mostly 

 simple, 1.5-4 dm. high; leaves twice pinnately dissected; inner bracts united to 

 the middle, broadly scarious-margined; ligules 8-12 mm. long; awns of the pappus 

 very short, about half as long as the width of the achenes. Plains and mountain 

 valleys: Colo. Submont. Mont. 



3. T. intermedium Rydb. A glabrous bushy biennial or perhaps perennial; 

 stems several, 2-6 dm. high; leaves once or twice pinnately divided; involucre 

 about 1 cm. broad; outer bracts very narrowly linear-lanceolate, about half as 

 long as the inner, these united to about the middle, scarious-margined; ligules 

 10-12 mm. long; teeth of the pappus longer than the width of the achenes. On 

 plains in dry or sandy soil: Neb. Wyo. Colo. Plain Submont. Je-Au. 



4. T. ambiguum A. Gray. Stem 2-4 dm. high; leaves once or twice pin- 

 nately divided; upper stem-leaves much reduced, often simple; outer bracts 

 very short, ovate or elliptic, 1-2 mm. long, obtuse, the inner very broadly scar- 

 ious-margined. In dry soil: N.M. Colo. Son. Je-Jl. 



5. T. subnudum A. Gray. Stem subscapose, 1-3 dm. high; leaves pin- 

 nately or bipinnately divided into linear or linear-lanceolate divisions; outer 

 bracts short, oblong, about one-fourth as long as the inner, these broadly scarious- 

 margined; pappus a minute 4-5-toothed crown or obsolete. In dry soil: N.M. 

 Colo. Utah Ariz. Son Submont. My-Je. 



6. T. marginatum Rydb. Stem 1-2 dm. high, leafy mostly at and near 

 the base; leaves pinnately or bipinnately divided into linear divisions, 1-2 mm. 

 wide; peduncles mostly solitary, 7-10 cm. long; heads about 1 cm. broad; outer 

 bracts oblong, about one-third' as long as the inner, these united to the middle; 

 teeth of the pappus minute. On dry plains: Sask. Mont. Plain. My-S. 



7. T. gracile (Torr.) A. Gray. Stem 3-9 dm. high, branched and leafy; 

 leaves as in the preceding, the upper reduced and often simple; heads 12-15 mm. 

 broad; outer bracts oblong, obtuse, one-fourth as long as the inner, the latter 

 united to the middle or beyond; awns of the pappus longer than the width of the 

 achenes. On plains and prairies: Neb. Tex. Ariz. Wyo. Plain Mont. 

 My-Au. 



81. PTILONELLA Nutt. 



Loosely branched annuals. Leaves alternate, narrowly linear, entire. Heads 

 radiate. Bracts of the involucre narrow, subequal, in two series. Receptacle 

 convex; paleae thin or scarious, narrow. Ray-flowers 3-6, pistillate and fertile; 

 ligules white, 3-cleft. Disk-flowers 7-12, hemaphrodite, fertile, or the central 

 one sterile; corollas white, 5-cleft. Style of the fertile disk-flowers with two 

 short branches, that of the infertile central one entire. Pappus of many narrow, 

 linear or aristiform, fimbriate-lacerate squamellae, sometimes wanting. [Ble- 

 pharipappus Hook., in part.] 



1. P. scabra (Hook.) Nutt. Annual; stem 1-3 dm. high, branched, puberu- 

 lent, sometimes also sparingly hispid, more or less glandular above; leaves alter- 

 nate, narrowly linear, entire, scabrous; heads short-peduncled; involucres 6-7 

 mm. high, 7-10 mm. broad; bracts oblong, glandular-puberulent ; ligules white, 

 6-7 mm. long; disk white. Blepharipappus scaber Hook. Dry plains and 

 mountains: Wash. Ida. Nev. Calif. Son. Submont. Ap-Jl. 



