Western silvery aster

Aster sericeus Ventenat, Descr. Pl. Nouv., plate 33. 1800; Lasallea sericea (Ventenat) Greene; Virgulus sericeus (Ventenat) Reveal & Keener

Perennials, (20–)30–70 cm, cespitose, eglandular; with short, woody, cormoid caudices, or short rhizomes. Stems 1–5+, ascending to erect (thin, grayish brown to dark brown), glabrous proximally, densely canescent distally. Leaves (silvery) firm, soft; basal withering by flowering, sessile, blades (1–3 nerved) elliptic-lanceolate, 10–40 × 5–15 mm, bases cuneate, weakly sheathing, margins usually entire, rarely remotely serrate, piloso-ciliate, apices acute, faces less copiously hairy than cauline; proximal cauline withering by flowering, sessile, blades oblanceolate or oblong to linear-lanceolate, 15–30(–50) × 4–10 mm, slightly and progressively reduced distally, bases rounded, sub­clasping, margins entire, silky-pilose, apices obtuse to acute, mucronulate, faces sparsely to densely silky-pilose; distal sessile, blades lanceolate, 10–30 × 5–8 mm, little reduced distally, bases cuneate, margins entire, apices acute, mucronate, faces ± densely silky. Heads in open, paniculiform arrays, branches sparse, fastigiate, often arching (1–5+ per branch). Peduncles subsessile or 0.5–3(–5) cm, densely sericeo-strigose, bracts crowded, 4–8(–10) mm, grading into phyllaries. Involucres campanulate to cylindric, (5–)7.5–10 mm. Phyllaries in 3–5(–6) series, outer ovate with expanded distal portion [(4–)5–6 mm], mid ovate-lanceolate [6–8(–10) mm] with expanded green portions, inner linear, unequal or sometimes subequal, outer often foliaceous, bases (mid) scarious, margins silky, green zones restricted to expanded distal ¹ / 2 – ² / 3 (obscured by hairs), apices (outer) spreading or squarrose to reflexed, acute, mucronulate, faces densely long-silky. Ray florets (10–)15–30; corollas usually rose-purple to deep purple, rarely white, laminae 8.5–11 × 1–1.5 mm. Disc florets (15–)25–35; corollas pink turning purple, (5–)5.5–7 mm, tubes shorter than narrowly funnelform throats (both thinly puberulent), lobes deltate, 0.7–0.9 mm. Cypselae purple or brown, obovoid, not compressed, 2–3 mm, 7–10-nerved (prominent), faces glabrous; pappi whitish or tawny, 6–7 mm. 2n = 10, 20.

Flowering Aug–Oct. Open, dry, deep, sandy or loamy soils, broken limestone outcrops, open-wooded bluffs, open woods, open calcareous hammocks, prairies, fields, sand barrens, dunes, dry banks, rarely acidic shield rocks; 100–500+ m; Man., Ont.; Ark., Ga., Ill, Ind., Iowa, Kans., Mich., Minn., Mo., Nebr., N.Dak., Ohio, Okla., S.Dak., Tenn., Tex., Wis.; West Indies (Bahamas).

Symphyotrichum sericeum is known in the Bahamas as S. lucayanum (Britton) G. L. Nesom [syn. Aster lucayanus Britton, Virgulus lucayanus (Britton) Reveal & Keener]. It is of conservation concern in Indiana, Michigan, and Canada. Symphyotrichum sericeum is distinct and unlikely to be confused with other species due to its silvery-silky leaves and phyllaries, open arrays, and cormoid rootstocks. Aster sericeus forma albiligulatus Fassett is a white form of the species, in contrast to the typically purple forma sericeus; these do not deserve formal recognition.