Hall's Aster

Symphyotrichum hallii is restricted to open habitats of the Puget Trough of western Washington and the Willamette Valley of western Oregon, with outlying stations in the Columbia Gorge and central Washington. Some of the polyploid races appear to be alloploids involving the sympatric S. subspicatum, with larger leaves and fewer, larger heads with violet rays.

Perennials, 30–60 cm, colonial; long-rhizomatous. Stems 1–6, ascending to erect, glabrous or puberulent, especially distally. Leaves thin, margins entire, apices acute, faces glabrous or scabridulous; basal withering by flowering, petiolate, blades narrowly oblanceolate to linear, 10–60 × 2–10 mm, attenuate, margins entire; proximalmost cauline sometimes withering by flowering, sessile, blades linear to narrowly oblanceolate, 30–80 × 2–8 mm, bases cuneate, apices acute; distal sessile, blades linear, 10–50 × 2–8 mm, bases ± cuneate, truncate. Heads in racemiforn to paniculiform arrays, branches usually less than 10(–20) cm. Peduncles sparsely to densely hairy, bracts 3–10, linear to narrowly elliptic, much smaller than distal leaves. Involucres campanulate, 4–7 mm. Phyllaries in 5–6 series, appressed, narrowly oblanceolate (outer) to linear (inner), unequal, bases (outer) herbaceous or scarious less than ¹ / 2 , margins entire, green zones ovate to linear (inner), apices obtuse, faces glabrous. Ray florets 14–35; corollas usually white, sometimes pale violet, laminae 7–12 × 1–2 mm. Disc florets 20–35; corollas yellow, 4.5–6.5 mm, lobes triangular, 0.7–1 mm, glabrous. Cypselae brown, cylindric to obovoid, not compressed, 2–2.5 mm, 2–5-nerved, faces hairy; pappi white, 5–7 mm. 2n = 16, 32, 48.

Aster hallii A. Gray in A. Gray et al., Syn. Fl. N. Amer. 1(2): 191. 1884; A. chilensis Nees subsp. hallii (A. Gray) Cronquist

Symphyotrichum hallii (formerly Aster hallii) is a species of flowering plant in the family Asteraceae endemic to western Oregon and Washington states. Commonly known as Hall's aster, it is a perennial, herbaceous plant with a long rhizome that creates colonies of itself. It grows about 30–60 centimeters (1–2 feet) tall, and has white (sometimes pale violet) rays that open July–August.

Most occurrences of the species have been found at elevations of 0–500 meters (0–1,640 feet) in open areas in the Puget Sound region and Willamette Valley, with outliers in Columbia Gorge and central Washington. It is conservationally Imperiled (S2) in Washington state.