Flower:

Branching clusters of stalked flowers at the top of the stem and arising from upper leaf axils, typically with 20 or more flowers per branch. Rarely, flowers are all on one side of a branch (secund). Flowers are ½ to ¾ inch across, occasionally 1 inch, with 16 to 50 narrow petals (ray flowers) and a yellow center disk that turns reddish with age. Ray color is typically white, sometimes blue to violet.

The bracts (phyllaries) surrounding the base of a flower are in 3 to 6 layers, lance-linear, appressed to slightly spreading, green but pale at the base, somewhat hairy, and the outer layer shorter than the inner. Flower stalks are variously hairy, sometimes in lines, with 1 to several small leaf-like bracts below the flower.

Leaves and stems:

Leaves are thin, mostly lance-linear, 1 to 4 inches long, up to ¾ inch wide, toothless or with a few widely-spaced teeth, hairless except for minute hairs around the edge, pointed at the tip, and mostly stalkless. Basal leaves are broader and more variable in shape, with winged, sheathing stalks; they wither away by flowering time along with the lower stem leaves. Withered leaves are brown and curled and tend to persist on the stem rather than fall off.

Stems are erect though sometimes flop over from the weight of the flowering branches, round or shallowly grooved, and mostly smooth except for lines of short hairs in the upper plant and into the flowering branches. Colonies can be formed from long rhizomes.

Fruit:

Fruit is a dry seed with a tuft of dull white to yellowish hairs to carry it off in the wind.

Notes:

Panicled Aster is the most common of the white asters in Minnesota and throughout much of North America. There are a number of asters with small, white flowers in Minnesota and it can be a real challenge to keep them straight. Panicled Aster is distinguished by a combination of characteristics: ½ to ¾-inch flowers with 16 to 50 rays, generally lance-linear leaves that are hairless except around the edges, stems smooth or hairy in lines, and often 100 or more flowers per plant, sometimes congested on lateral branches. By comparison with other white asters having a generally similar leaf shape, Calico Aster (Symphyotrichum lateriflorum), Ontario Aster (S. ontarionis) and Awl Aster (S. pilosum) all have leaves with hairs along the midvein and/or surfaces and (usually) stems covered in hairs, not in lines. Northern Bog Aster (S. boreale) has proportionately narrower leaves, larger flowers about 1 inch across, and is typically a more spindly plant with few flowers.

There are up to 5 varieties of S. lanceolatum (depending on the reference), 3 of which have been recorded in Minnesota; var. hesperium (a.k.a. Aster herperius) usually has large leafy bracts below the (more typically) blue-violet flowers, outer phyllaries 2/3+ the length of the inner, lower leaves shallowly serrate; var. interior has flowers with 22 to 24 rays congested on lateral branches, inner phyllaries up to 3.7 mm long, outer phyllaries 1/3 to 2/3 the length of the inner and lack large leafy bracts; var. lanceolatum the most common with inner phyllaries up to 5.1 mm long, outer phyllaries 1/3 to 2/3 the length of the inner, flowers not usually congested near branch tips.