Zigzag Aster (Aster prenanthoides)
Now Symphyotrichum prenanthoides. Blue asters are among the last flowers of the fall. Identifying asters is, of course, a foolish endeavor, but this one has the clasping leaves and zigzag stem that identify a Zigzag Aster. It was blooming at the edge of the woods near the parking lot of the Pittsburgh Zoo in late October.
From Gray’s Manual:
A. prenanthoides 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 rather 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. Minn, and Ia. Aug.-Oct.