White Arrowleaf Aster

The name Aster sagittifolius Wedemeyer ex Willdenow has been misapplied to this taxon; our interpretation of the type of this entity concords with that of A. G. Jones (1980), i.e., that it is conspecific with the type of Symphyotrichum cordifolium or a garden hybrid involving the latter. Aster sagittifolius forma hirtellus (Lindley) Shinners is not recognized here.

Perennials, 40–120(–200) cm, cespitose; short-rhizomatous or with stout, branched caudices. Stems 1–5+, erect (straight to slightly flexuous, brittle, sometimes stout), proximally glabrous or glabrate, distally sparsely pilose. Leaves thin, margins usually shallowly, sometimes deeply serrate, rarely entire (distal), (piloso- to strigoso-)ciliate to scabrous (distal), apices mucronate, abaxial faces moderately pilose, ± densely so on midveins, adaxial glabrate to sparsely pilose or scabrous; basal usually withering by flowering, sometimes persistent, long-petiolate (5–15 cm, petioles not or narrowly winged, sheathing), blades ovate to lance-ovate or lanceolate, 25–120 × 15–50 mm, bases usually shallowly, sometimes deeply, cordate to truncate or rounded, apices acute, sometimes rounded; proximal cauline sometimes deciduous at flowering, winged-petiolate (petioles distally usually broader-winged, clasping), blades ovate to lanceolate, 50–120 × 20–50 mm, gradually reduced distally, bases usually truncate or rounded to attenuate, sometimes cordate, apices usually acute or acuminate, sometimes nearly caudate; distal ± shortly winged-petiolate or sessile, blades lance-ovate or lanceolate to linear-lanceolate, 10–100 × 1–25 mm, reduced distally, bases attenuate to cuneate, margins entire to subentire, scabrous, apices acuminate to subcaudate. Heads (crowded) in dense, elongate, paniculiform arrays, branches stiffly ascending to erect (sometimes arched when long, peduncles then often secund), usually racemiform, sometimes paniculiform, leafy. Peduncles 0.3–2 cm, sparsely pilosulous to glabrate, bracts many, ascending, linear to subulate, 2–4 mm, grading into phyllaries. Involucres cylindric, (4–)4.5–6(–7) mm. Phyllaries in 4–6 series, appressed or recurved-spreading, subulate (outer) to linear-lanceolate (inner), unequal, bases indurate ¹ / 3 – ¹ / 2 +, margins scarious, hyaline, erose, sparsely ciliolate (mostly distally), green zones linear-lanceolate (outer) to linear (inner), apices long-acuminate to caudate, recurved, hyaline-mucronate to aristate, tips often purple, faces glabrous. Ray florets 8–15(–20); corollas mostly white to pale pink or lilac or light blue, laminae 4.5–8(–10) × 0.8–1.5 mm. Disc florets (8–)10–15(–20); corollas whitish to cream becoming pink, (3.5–)4–5 mm, tubes shorter than funnelform throats (with hairs), lobes lanceolate, 0.4–0.7 mm. Cypselae tan to brown or dull purple (nerves stramineous), obovoid, ± compressed, 1.8–2.5 mm, 4–6-nerved, faces glabrous or glabrate or very sparsely strigillose; pappi white or rose-tinged, 3–4 mm. 2n = 16.

Aster urophyllus Lindley ex de Candolle in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 233. 1836; A. sagittifolius Wedemeyer ex Willdenow var. dissitiflorus E. S. Burgess

Symphyotrichum urophyllum (formerly Aster urophyllus) is a species of flowering plant in the family Asteraceae native to eastern North America, commonly known as arrowleaf aster.