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The upper stems and branches (some arising from upper leaf axils) of white arrowleaf aster terminate in 6-18" long panicles of flowerheads; the panicles are 2-3 times longer than wide. Each flowerhead is 1/2-3/4" across with 8-15 pistillate, white (rarely pale lavender) ray florets and 10-15 perfect (both stamens and styles present) disk florets. The disc florets are initially yellow but turn pink or light purple with age such that the flowerheads with yellow disk florets are often in the minority on the plant. The individual disk florets strike me as being larger than on many asters. The phyllaries (bracts) covering the base of the flowerhead are narrowly lance-shaped, usually hairless, dark green in the middle tapering to narrow, stiff, green to purplish tips. The fruits are 2 mm long, purplish-brown dry seeds with longitudinal ribs and a tuft of hairs at one end. White arrowleaf aster is similar to Drummond's aster (Symphyotrichum drummondii) but is less hairy and has distinctly different phyllaries. Among asters with white flowerheads, only white arrowleaf aster has heart-shaped leaves. (Other asters with heart-shaped leaves typically have blue to violet flowers.)

Symphyotrichum

Symphyotrichum urophyllum

white arrowleaf aster [Blooms: Aug/Sep – ?]