974 CARDUACEAE 



outer linear or oblong, densely canescent, the inner oval; flowers brownish. A. 

 trifida Nutt. Plains: Mont. Colo. Nev. Ore. Wash. Plain Mont. Au-S. 



70. A. rigida (Nutt.) A. Gray. Undershrub, 2-4 dm. high; branches rigid, 

 slightly canescent when young, soon glabrate, leafy to the top; leaves rigid, 

 silvery-canescent, linear-filiform, 3-cleft, or the upper and those of the fascicles 

 entire, 1-2 cm. long; heads solitary (rarely 2 or 3), sessile in the axils of the leaves; 

 involucres 3 mm. long, 1.5-2 mm. wide, 5-12-flowered ; bracts oval, well imbri- 

 cate, hyaline-margined; corollas tinged with purple. Rocky ridges: Ore. Ida. 



-Wash. Son. Au-O. 



71. A. pygmaea A. Gray. Perennial, with a woody, cespitose caudex; 

 branches 1 dm. high or less, slightly canescent or glabrate; leaves 5-10 mm. 

 long, rigid, pinnatifid with 3-7, linear-subulate divisions, thick, glabrous above, 

 slightly canescent beneath; heads few, in a short spike-like inflorescence; invo- 

 lucres 45 mm. long, 2-3 mm. broad, 3-4-flowered; bracts imbricate, the outer 

 lanceolate, the inner elliptic. Desert regions: Nev. Utah. Son. Au-S. 



124. PETASITES L. SWEET COLTSFOOT, BUTTERBUR. 



Perennial herbs, with thick creeping rootstocks. Leaves basal, long-peti- 

 oled, with ample reniform, cordate, triangular, or sagittate blades, usually tomen- 

 tose beneath, appearing later than the scaly-bracted flowering stems. Heads 

 racemose or corymbose, subdioecious. Involucre campanulate; bracts in one 

 series, herbaceous. Flowers of the fertile plants, all or most of them pistillate, 

 fertile; corolla irregularly 2-5-toothed and cylindric, or else ligulate. Flowers 

 of the substerile plant mostly hermaphrodite, but sterile, and a few pistillate 

 ones at the margin; corolla of the sterile flowers tubular and 5-toothed; style 

 2-lobed, but ovary sterile. Achenes narrow, 5-10-ribbed. Pappus of soft white 

 bristles. 



Leaf-blades sagittate or cordate, pinnately veined (except in P. viti folia). 

 Leaves not cleft. 



Leaves repand-denticulate, with numerous teeth. 1. P. sagittata. 



Leaves angulately and sinuately few-lobed. 2. P. frigida. 



Leaves cleft one-third to one-half to the midrib ; lobes dentate. 



Leaves not broader than long; only one pair of lateral veins rising from the base. 



3. P. corymbosa. 

 Leaves decidedly broader than long; two or more pairs of lateral veins rising from 



the base. 4. P. vitifolia. 



Leaves round-reniform, pedately veined and lobed. 5. P. palmata. 



1. P. sagittata (Pursh) A. Gray. Leaf-blades cordate, ovate-cordate to 

 deltoid-cordate, 1-3 dm. long, 1-2 dm. wide, with a deep basal sinus, glabrate 

 above, white-tomentose beneath; scape 2-3 dm. high; heads corymbose; invo- 

 lucres obconic, 8-9 mm. high, glandular-pubescent as well as tomentose; ligules 

 of the substerile heads 5-7 mm. long, 1-1.5 mm. wide, those of the subfertile 

 heads smaller, 3-5 mm. long, less than 1 mm. wide. Tussilago sagittata Pursh. 

 Petasites dentata Blankinship. Wet grounds: Lab. Minn. Colo. Alaska. 

 Plain Mont. My-Jl. 



2. P. frigida (L.) Fries. Leaf -blades deltoid or cordate, with an open basal 

 sinus, 2-10 cm. long and as broad, sinuately few-lobed or coarsely dentate; lobes 

 or teeth 11-20; heads racemose-corymbose; involucres about 1 cm. high, tomen- 

 tulose and glandular-pubescent; bracts oblong, obtuse, purplish; ligules of the 

 substerile heads about 8 mm. long and 1.5-2 mm. wide, those of the subfertile 

 heads about 2 mm. long and 0.5 mm. wide. Wet places: Mack. B.C. Alaska; 

 n Eu. Alp. Je-Jl. 



3. P. corymbosa (R. Br.) Rydb. Leaf-blades broadly deltoid or cordate 

 in outline, 3-10 cm. long and broad, deeply cleft, the lobing extending one-third 

 to one-half the distance to the midrib; divisions again lobed or dentate, with tri- 

 angular lobes or teeth; peduncles 2-3 dm. high; heads corymbose; involucres 

 8-10 mm. high, glandular-pubescent, scarcely tomentose; ligules of the substerile 

 heads 5-7 mm. long, 1.5 mm. broad, those of the subfertile heads 2 mm. long, 

 0.5 mm. wide. Nardosmia corymbosa R. Br. P. palmata frigida Macoun. 

 Wet places: Alta. B.C. Alaska. Subalp. Je-Au. 



