Erigeron gracilis Rydb.

Erigeron gracilis "differs from E. ursinus in the strigose and scarcely glandular pubescence of the involucre, narrower and less herbaceous phyllaries, narrower and on the average longer disc-corollas, simple or nearly simple pappus, narrower ligules, on the average, and ordinarily narrower and slightly hairier leaves. E. gracilis grows at lower elevations than E. ursinus, in a drier habitat, and has a much more restricted range" (A. Cronquist 1947, p. 162). The two species are sympatric in northwestern Wyoming.

Perennials, 5–20 cm; rhizomatous, fibrous-rooted, forming diffuse systems of slender, rhizomelike caudex branches. Stems ascending (bases usually purplish), glabrous or sparsely strigose (or hairs loosely spreading), eglandular. Leaves basal (persistent) and cauline; basal (purplish) and proximal cauline blades oblanceolate to oblong, 20–40(–90) × 1–3(–5) mm, cauline reduced distally, margins entire, glabrous or sparsely strigose (or hairs loosely spreading), eglandular. Heads 1. Involucres 5–7.5 × 10–15 mm. Phyllaries in 2–3(–4) series (margins and tips often purplish, loose, linear-lanceolate, apices spreading), sparsely strigoso-hirsute to strigose (hairs appressed or slightly loose), sometimes minutely glandular. Ray florets 40–100; corollas blue to pinkish purple, 7–14 mm, laminae not coiling or reflexing. Disc corollas 4.1–5.6 mm. Cypselae 2 mm, 2-nerved, faces sparsely strigose; pappi: outer of setae, inner of 14–21 bristles. 2n = 18.

Erigeron ursinus D. C. Eaton var. gracilis (Rydberg) A. Nelson

Erigeron gracilis is a North American species of flowering plant in the family Asteraceae known by the common name quill fleabane.

Erigeron gracilis is native to the Rocky Mountains of the United States, in the states of Idaho, Montana, and Wyoming. Some of the known populations lie inside Yellowstone National Park.

Erigeron gracilis is a perennial herb up to 20 cm (20 inches) tall, spreading by means of underground rhizomes. The plant generally produces only one flower heads per stem. Each head contains as many as 10 blue or purple ray florets surrounding numerous yellow disc florets.