The white form of the Zigzag Aster (for which the preferred botanical name is now Symphyotrichum prenanthoides) is not terribly rare, though far less common than the blue form. Here we see the white form in the foreground, and the blue in the background. All shades between pale blue and white occur, so it’s very hard to mark where blue ends and white begins.
This plant was growing along a trail in Bethel Park, where it was blooming in early October.
We repeat the description we gave when we presented the blue form:
Flowers. Heads about an inch and a quarter wide, in irregular corymbs; disk flowers yellow, fading to red-brown; rays pale blue or violet, sometimes white, linear, numerous.
Leaves. Variable: alternate; lanceolate or ovate-lanceolate, with sharp and narrow points; strong central rib; rough, outward-facing hairs noticeable when rubbed toward stem; lower leaves on petioles with broad wings clasping the stem; upper sessile and clasping. On some plants the leaves are jaggedly toothed; on others the teeth are less prominent, with the upper leaves almost entire.
Stem. Tough, wiry; with purplish vertical lines; arching, about 1 or 2 feet high; characteristically zigzag from leaf to leaf, as in the picture at right.
Gray describes the genus Aster and the species:
ÁSTER [Tourn.] L. STARWORT. FROST-FLOWER. ASTER. Heads many-flowered, radiate; the ray-flowers in a single series, fertile. Bracts of the involucre mure or less imbricated, usually with herbaceous or leaflike tips. Receptacle flat, alveolate. Achenes more or less flattened; pappus simple, of capillary bristles (double in §§ 4 and 5). — Perennial herbs (annual only in §§ 7 and 8), with corymbed, panicled, or racemose heads, flowering chiefly in autumn. Rays white, purple, blue, or pink; the disk yellow, often changing to purple. Species often without sharply defined limits, freely hybridizing. (Name aster, a star, from the radiate heads of flowers. )
A. prenanthoìdes Muhl. Stem 1 m. or less high, corymbose-panicled, hairy above in lines; leaves rough above, smooth underneath, ovate to lanceolate, sharply cut-toothed in the middle, conspicuously taper-pointed, and rathrr abruptly narrowed to a long contracted entire portion, which is abruptly dilated into a conspicuously auricled base; heads on short divergent peduncles; involucre 5-8 mm. high; bracts narrowly linear, tips recurved-spreading; rays violet. — Borders of streams and rich woods, w. N. E. to Va. and Ky., w. to Minn, and la. Aug.-Oct.