Rigid Whitetop Aster

Symphyotrichum retroflexum is known only from the Appalachian Blue Ridges. It is possible that the species is an allopolyploid derived from members of subsections Cordifolii and Symphyotrichum.

Perennials, 40–100 cm, usually colonial, sometimes ± cespitose; short-(seldom long-)rhizomatous. Stems 1–2+, erect (straight to slightly flexuous, sometimes robust), glabrous. Leaves thin to firm, margins slightly recurved, scabrous, faces glabrous; basal mostly withering by flowering, petiolate (petioles narrowly winged, sheathing), blades lanceolate-ovate to ovate or spatulate, 25–110 × 10–40 mm, bases usually rounded to attenuate, seldom ± cordate, margins serrulate to shallowly serrate, apices obtuse to acute; proximal cauline often withering by flowering, petiolate (petioles ± widely winged, ± clasping), blades lance-ovate or narrowly ovate, 50–95 × 19–31 mm, bases usually rounded to attenuate, sometimes cuneate, rarely sub­cordate, margins serrate to serrulate; distal winged-petiolate or subpetiolate or sessile, blades lance-ovate or narrowly ovate to lanceolate or sometimes linear (in arrays), 7–1.5 × 3–31 mm, gradually and strongly reduced distally, bases cuneate, scarcely or not clasping, to slightly rounded and ± clasping, margins serrulate or entire, apices acute to acuminate. Heads in broad (appearing ± corymbiform) or narrow, paniculiform to ± racemiform arrays, branches usually long (to 10 cm), ascending to divaricate. Peduncles (when present) 0.2–1.5 cm, densely pilose or pilosulous, bracts 1–6+, lanceolate to oblong-lanceolate, foliaceous to distally grading into phyllaries. Involucres campanulate, (6–)7–10 mm. Phyllaries in 3–4(–5) series, broadly lanceolate constricted to narrow oblong bases (outer) to oblong-lanceolate or linear-lanceolate (inner), ± unequal, bases indurate ¹ / 10 – ¹ / 5 (outer) to ⁴ / 5 + (inner), margins hyaline, narrowly scarious, erose (indurate portion), sparsely ciliolate (foliaceous portion), green zones foliaceous (outer) to distal ¹ / 5 – ¹ / 4 foliaceous (inner), basally truncate to lanceolate, apices spreading to squarrose, acute to acuminate, mucronulate, abaxial faces glabrous or glabrate, adaxial strigillose (foliaceous portion). Ray florets 13–30; corollas blue to purple, laminae (10–)15–17 × 1.6–3 mm. Disc florets 35–50+; corollas cream to pale yellow becoming pinkish, 5.8–6.8 mm, tubes shorter than funnelform throats, lobes lanceolate, 0.9–1.2 mm, glabrous. Cypselae tan, obovoid to oblanceoloid, compressed, 3–3.9 mm, 4–6-nerved, faces glabrous or sparsely strigillose; pappi whitish to reddish, 5.3–6 mm. 2n = 48.

Aster retroflexus Lindley ex de Candolle in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 244. 1836; A. curtisii Torrey & A. Gray

Symphyotrichum retroflexum (formerly Aster retroflexus) is a species of flowering plant in the family Asteraceae native to the southeastern United States. Commonly known as rigid whitetop aster, it is a perennial, herbaceous plant that may reach 40 to 100 centimeters (16 to 39 inches) tall. Its flowers have blue to purple ray florets and cream to pale yellow then pinkish disk florets. It is known only from the Blue Ridge Mountains in Alabama, Georgia, North Carolina, South Carolina, Tennessee, and Virginia, where it grows in wooded areas at elevations of 400–1,500 meters (1,300–4,900 feet). As of September 2021, NatureServe classified it as Apparently Secure (G4); it had been reviewed last in 1994 and is marked as "needs review". There is an introduced presence of S. retroflexum in southeast China.

S. retroflexum herbarium specimen