Flower:

Open branching clusters at the top of the plant and arising from upper leaf axils, the branches stiff and usually ascending. Flowers are about 1 inch across with 15 to 30 petals (ray flowers) and yellow center disc flowers that turn reddish with age. Ray color is light to medium blue or purplish, rarely white.

The bracts (phyllaries) surrounding the base of the flower are 4 to 6 layers, narrow, appressed to slightly spreading, light green with a darker green, lance to diamond-shaped tip that may have a dot of red at the apex and few minute hairs around the edge. Flower stalks are up to 2½ inches long, hairless or minutely hairy in lines, with a few leaf-like bracts below the flower.

Leaves and stem:

Leaves are up to 4 inches long and 1½ inches wide, smooth and almost waxy, toothless or with a few shallow teeth, mostly hairless, and mostly clasp the stem. Basal leaves are somewhat variable in shape, from spatula-shaped to lance-oblong, have winged, sheathing stalks; basal and lower stem leaves typically wither away by flowering time but may persist.

Mid and upper stem leaves become smaller, nearly erect, more egg-shaped to lance-linear, rounded at the base or with a pair of small lobes (auricles) that wrap around and clasp the stem. Stems are single or multiple from the base, erect, hairless or with sparse hairs in the upper plant, and green or reddish.

Fruit:

Fruit is a dry seed with a tuft of light brown hair to carry it off in the wind.

Seeds are 2 to 4 mm long, brown to deep purple, oblong to narrowly cone-shaped, broadest near the tip, somewhat flattened with 4 or 5 longitudinal ridges.

Notes:

Smooth Blue Aster is similar to Sky Blue Aster (Symphyotrichum oolentangiense) and grows in a similar habitat, blooming at about the same time. The leaves of Sky Blue Aster are arrowhead shaped near the base and do not clasp the stem, its flowers are generally smaller, less than 1 inch across, and its phyllaries are appressed with a small, green, diamond-shaped tip. There are as many as 4 varieties of S. laeve, var. concinnum and var. purpuratum are more southern and/or eastern species, with var. laeve and var. geyeri reported as present in Minnesota. The DNR lists var. geyeri as “historical” and there are no records of it in the Bell Herbarium. Flora of North America notes that the difference between it and var. laeve is essentially only the shape of the dark green part of the phyllaries and they might be considered synonyms. Taxonomists can hash that one out.