Flower:

Branching clusters of stalked flowers at the top of the stem and arising from upper leaf axils. Branches are widely spreading, arching or ascending, with flowers usually all on one side of the branch (secund). Flowers are ½ to ¾ inch across with 15 to 35 petals (ray flowers) and a yellow center disk that turns reddish with age. Ray color is white, rarely pinkish or pale violet.

The bracts (phyllaries) surrounding the base of the flower are in 4 to 6 layers, appressed to slightly spreading, mostly light green with a long, darker green tip that may have a few hairs around the edge. The phyllary edges are often rolled under giving the green tip a very slender appearance; surfaces are hairless to sparsely minutely hairy. Flower stalks are ¼ to 1¼ inch long and spreading-hairy, with a few hairy, linear bracts below a flower. Phyllaries and bracts have a minute spine at the tip.

Leaves and stems:

Leaves are mostly lance-elliptic to lance-linear, sometimes widest above the middle, 1 to 4 inches long, up to 1 inch wide, toothless or shallowly toothed, pointed at the tip, stalkless or nearly so, typically with fairly large clusters of small leaves (fascicles) in the axils. Basal leaves are more spatula-shaped, rounded at the tip, with winged, sheathing stalks; basal and the lowest stem leaves wither away by flowering time.

Leaf surfaces are sparsely to densely covered in long, spreading hairs, with shorter hairs all around the leaf edge. Stems are single or multiple from the base, ascending to erect, densely covered in long, spreading hairs.

Fruit:

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

Notes:

Considered weedy in some parts of the country, Awl Aster can pop up in the disturbed soils of roadsides, shores, old fields and pastures. There are a number of asters with small, white flowers in Minnesota and it can be a real challenge to keep them straight. Awl Aster is distinguished by a combination of characteristics: ½ to ¾-inch flowers with 15 to 35 rays, typically arranged all on 1 side of a branch (secund), phyllaries with rolled edges and a minute spine the tip, (usually) long spreading hairs on stems and leaf surfaces, and relatively large clusters of small leaves (fascicles) in many leaf axils. By comparison with other white asters having a generally similar leaf shape, Calico Aster (Symphyotrichum lateriflorum) and Ontario Aster (S. ontarionis) may have similar branching, but flowers not more than ½ inch across. Calico Aster also has flowers with only 9 to 15 rays, a pale center disk (not bright yellow), and leaves with short hairs only along the midvein; Ontario Aster flower stalks are not more than 1/3 inch long and phyllaries are more oblong and do not have rolled edges or a spine at the tip. Northern Bog Aster (S. boreale) and Panicled Aster (S. lanceolatum) leaves are hairless except around the edges and have only lines of hairs on stems. Awl Aster was once treated as a variety of Heath Aster (S. ericoides), which, like Awl Aster, has a spine at the tip of bracts and may also be secund, but is easily distinguished by the smaller linear leaves, broader, flat, flaring phyllaries with a larger spine, and appressed to ascending hairs on stems, where Awl Aster has spreading hairs.

There are 2 recognized varieties of S. pilosum: var. pringlei, which is essentially hairless or hairy in lines and is found from Nova Scotia west to Wisconsin and south to North Carolina (it is reputedly in Minnesota though no records exist at the Bell Herbarium); var. pilosum is densely hairy as described above. The common name “Awl” comes from the shape of the phyllaries that have rolled edges.