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..
Erigeron uniflorus L. Sp. Pl. 864. 1753- Perennial by short branching rootstocks; stems slender, single or .tufted, more or less pubescent, simple, erect, 1'-10' high. Basal leaves petioled, spatulate, obtuse, entire, 1-2' long; stem leaves sessile, lanceolate or linear-lanceolate, entire, acute or obtuse; head solitary, peduncled, 1/2'-l' broad; rays about 100, purple or purplish, 2"-4" long; involucre hemispheric, its bracts linear-lanceolate, acute, copiously woolly; pappus simple.
Labrador and Arctic America to Alaska, south in the Rocky Mountains to Colorado and in the Sierra Nevada to California. Also in Europe. Summer.
Erigeron asper Nutt. Gen. 2: 147. 1818. Erigeron glabellus Nutt. loc. cit. 1818.
Perennial by a woody root; stem simple, or branched above, more or less pubescent, sometimes hirsute, 6'-24' high. Leaves glabrous, pubescent or ciliate, entire, the basal ones spatulate, obtuse, 2-4' long, 3"-1' wide, narrowed into margined petioles; stem leaves oblong-lanceolate or linear-lanceolate, obtuse or acute, the upper smaller; heads several or solitary, slender-peduncled, 1-2' broad; involucre hemispheric, its bracts linear, acute, hirsute or pubescent; rays 100-150, very narrow, violet, purple, or nearly white, 4"-7" long; pappus double, the outer row of bristles much shorter than the inner.
In dry soil, Minnesota to Wisconsin, Nebraska, Manitoba, Utah and New Mexico. Races differ in pubescence. June-Sept.
Erigeron subtrinervis Rydberg, Mem. Torr. Club 5: 328. 1894.
Similar to the preceding species, perennial by a woody root, finely pubescent all over; stems leafy to the inflorescence. Leaves entire, thin, the basal and lower ones oblanceolate to oblong, obtuse or acute, petioled, the upper lanceolate or ovate-lanceolate, sessile or somewhat clasping, acute, rather distinctly 3-nerved; heads 1'- 1 1/2' broad, corymbose, or rarely solitary; involucre hemispheric, hirsute; rays numerous, blue to pink; pappus double, the outer bristles very short.
In dry soil, South Dakota to Wyoming, Nebraska, Utah and New Mexico. July-Sept.
Diplopappus canescens Hook. Fl. Bor. Am. 2: 21.
Perennial by a deep root; stems tufted, canes-cent, simple, or branched above, 6'-12' high. Leaves canescent or pubescent, entire, the lower and basal ones petioled, narrowly oblanceolate or spatulate, obtuse or acutish, 1-3' long; stem leaves linear or linear-oblong, acute or obtuse, sessile, the upper gradually shorter, heads solitary or several, short-peduncled, 1'-l 1/2' broad; involucre hemispheric, its bracts lanceolate or linear-oblong, acute, canescent; rays 40-60, 3"-6" long, white or pinkish; pappus double, the outer series of bristles very short.
In dry soil, Manitoba to Yukon, Nebraska (according to Webber), British Columbia and Colorado. June-Aug.