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. margmalum. 



Plants 3-6 dm. liigh; 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— Suhmont. Je-Au. 



2. T. tenue Eydb. 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 haH as long as the width of the achenes. Flams and mountain 

 valleys: Colo. Suhnont. — Mont. 



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

 stems several, 2-6 dm. high; leaves once or twice pmnately 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. Un 

 plains in dry or sandy soil: Neb.— Wyo.— Colo. Plain— Suhmont. 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 smiple; 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 crowTi or obsolete. In dry soil. i% .M.— 

 Colo.— Utah— Ariz. Son—Svhmont. My-Je. 



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

 the base; leaves pmnately or bipinnately divided into linear divisions 1-2 mm 

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

 bracts oblong, about one-thnd as long asthe inner, these umted 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 if the preceding, the upper reduced and often snnple; heads 12-15 mm 

 broad- outer bracts oblong, obtuse, one-fourth as long as the mner. tl^e latter 

 Sted to the middle or beyond;.awns of the pappus longer than the w^U^oJthe 

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



My-Au. 



81. PTILONELLA Nutt. 



Looselv branched annuals. Leaves alternate, narrowly Unear, entire. Heads 

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

 radiate. iDrdLih ui ^"'^ . narrow Ray-flowers 3-6, pistillate and fertile; 

 convex; P/^ f %thin or ^^^^^XVeS 7- 2, hemaphrodite, fertUe, or the central 

 hgules ^,h^te,3-c eft. D^k flowers ^ , P . disk-flowers Mith two 



Zrt bSn hS tha oT^The'lnfeS cenSal one entire. Pappus of many narrow, 

 iSr oTaSiform, fimbriate-lacerate squamellae, sometmies wanting. [Ble- 



-pharipappus Hook., in part.] 



sometimes 



dm. high 

 '«ndular — 

 peduncled 



nate narrow ime«,«u^^.^^-j-™.^ glandulartpuberulent ; Ugulej white 

 ?-?• If' long dSk \t4: X*«n>4A -^ ?oot Dry plaroB anj 



moxmtains 



I(ja_Nev— Calif. Son— Suhmont. Ap-Jl 



