412 Compositaceae 
PETASITES COLT’S-FOOT 
Herbs, perennial; rhizome thick, horizontal. Leaves all basal, pinnately or pal- 
mately veined, simple, alternate, long-petioled. Heads rayless or radiate, in a raceme or 
corymb, on large-bracted stems, appearing before the leaves, dioicous or somewhat sO; 
involucre-bracts soft, herbaceous; receptacle flat. Pistillate flowers the outer when mixed 
with staminate; corolla irregular,, 2—5-toothed to distinctly ligulate, white or purplish; 
style unbranched. Perfect but sterile flowers near center when mixed with pistillate, 
white or purplish, regular, 5-toothed; style branched. Akenes narrow, 5—10-ribbed. 
Pappus bristles soft, white, long. (Gk. petasos—a broad brimmed hat; referring to the 
leaves. ) 
A. Leaves reniform-orbicular, 1.54 dm. wide, 7—11-cleft. W. E. (P. palmata 
for our region.) P. speciosa Pip. (Large Colt’s-foot) 
AA. Leaves longer than wide, 0.5—2.5 dm. long. 
B. Leaves broadly sagittate, irregularly dentate to almost entire. FE. (P. dentata.) 
P. sagittata Gray (Arrow-leaf Colt’s-foot) 
BB. Leaves ovate or oblong, 5—-7-lobed; alpine. W. C. E. (C. nivalis.) 
P. frigida Fries (Arctic Colt’s-foot) 
RAILLARDELLA 
Herbs, acaulescent; rhizomes stout, creeping. Leaves basal, entire. Heads radiate 
or rayless, several- to many-flowered, solitary and terminal on simple naked scapes; in- 
volucre-bracts 6—14, linear, equal, in 1 series; receptacle flat or convex. Ray-flowers 
fertile, irregular, deeply 3—4-cleft, yellow. Disk-flowers regular, 5-toothed, yellow. 
Akenes linear, flattish, striate. Pappus-bristles rather stout, plumose. (Diminutive of 
Raillardia, another genus of Compositaceae. ) 
A. Leaves glabrous, 5—10 cm. long; scapes 30——45 cm. high; heads radiate, about 
40-flowered. C. R. pringlei Gr. 
AA. Leaves silvery-tomentose, 2.5——5 cm. long; scapes 5—10 cm. high; heads ray- 
less, 7—20-flowered. U.C. E. R. argentea Gray 
ARNICA ARNICA 
Herbs, perennial, erect. Leaves usually opposite. Heads rayless or radiate, many- 
flowered, rather large; involucre campanulate; its bracts several, thin-herbaceous, in 12 
series, oblong-lanceolate to linear, equal; receptacle flat, villous or minutely fringed. Ray- 
flowers yellow, perfect. Disk-flowers yellow, perfect, 5-toothed. Akenes linear, some- 
what 5—10-ribbed or angled. Pappus-bristles in | whorl, many, rather rigid, scabrous 
to barbellate. (Said to be from Gk. arnakis—=a lamb’s skin; referring to the softness of 
the heads. ) st 
A. Heads rayless. 
B. Involucre-bracts sparsely pubescent. U. C. E. 
A. parviflora Gray 
BB.  Involucre-bracts densely villous. 
C. Basal leaves truncate to cordate at base. C. E. (A. cordifolia eradiata. ) 
A. discoidea Benth. 
CC. Basal leaves cuneate or narrowed at base. W. C. E. (A. spathulata.) 
A. parryi Gray 
AA. Heads radiate. 
D. Basal leaves cordate to truncate at base. 

