This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Arnica mollis Hook. Fl. Bor. Am. 1: 331. 1833.
Villous-pubescent; stem simple, or little branched, 1°-2 1/2° high, bearing 1-6 heads at the summit. Leaves oblong or oblong-lanceolate, dentate or entire, acute or obtuse, 2-5' long, 3"-9" wide, the lower and basal ones narrowed into petioles, the upper sessile, and usually somewhat connate by a broad or narrowed base, those of the stem 3-5 pairs, usually with some alternate small ones on the branches; heads 1'-2' broad; bracts of the involucre acute; rays 10-15, 3-toothed; achenes hirsute-pubescent; pappus yellow-brown, plumose.
Mountains of northern New York, New Hampshire and Maine to New Brunswick, west to Lake Superior, British Columbia and California, south in the Rocky Mountains to Utah and Colorado. Included, in our first edition, in the northwestern A. Chamissonis Less. June-Aug.
Arnica chionopappa Fernald, Rhodora 7: 148. 1905.
Stem 15' high or less, villous to the base. Leaves thin in texture, the lower and basal ones ovate to lanceolate, acute, narrowed at the base, sharply dentate with few teeth, petioled, 2 1/2'-4 1/2' long, the upper few pairs narrowly lanceolate, entire, sessile; heads solitary or few, about 1 1/2' broad; involucre villous, 4"-S" high, its bracts linear-lanceolate, acuminate; rays 10-15; pappus bright white, barbellate.
On wet cliffs, Quebec and New Brunswick. June-July.
Arnica gaspensis Fernald, from ledges in Gaspe County, Quebec, has creamy-white pappus, the involucre and peduncles glandular-pubescent.
Arnica montana var. alpina L. Sp. Pl. 884. 1753. Arnica alpina Olin & Laden, Diss. 11. 1799. A. angustifolia Vahl, Fl. Dan. pl. 1524. 1814. A. plantaginea Pursh, Fl. Am. Sept. 527. 1814. A. Sornborgeri Fernald, Rhodora 7: 147. 1905.
Stem slender, 6'-15' high, villous or pubescent, and glandular or glabrous below; stem simple, usually bearing but a single head, but sometimes with 1-3 additional ones from the axils of the upper leaves. Leaves lanceolate, linear-oblong, or the lowest spatulate, thickish, entire or denticulate, 3-nerved, the basal ones petioled, those of the stem 1-4 pairs, sessile or short-petioled, scarcely connate, the upper pair usually much smaller than the lower ones; heads about 2' broad; rays 10-15, 3-toothed; achenes hirsute; pappus brownish.
Labrador to Greenland and the Arctic Sea, Also in northern Europe. Races differ in pubescence. Rocky Mountain plants formerly referred to this species appear to be distinct. May-Sept.