Flower:

Branching clusters of stalked flowers at the top of the stem and the end of branch tips. Flowers are ½ to ¾ inches across with 10 to 25 pale blue to bright blue-violet petals (ray flowers) and a yellow center disk that turns reddish with age.

The bracts (phyllaries) surrounding the base of the flower are hairless to minutely hairy, appressed, have green diamond shaped tips and may have a spot of purple at the apex. Flower and cluster stalks are hairless with several to many small leaf-like bracts.

Leaves and stems:

The leaves feel like fine sandpaper on both surfaces and are toothless or nearly so. Basal and lower stem leaves are mostly arrowhead to narrowly heart-shaped, to 4 inches long and 1¾ inches wide, pointed or blunt at the tip, and abruptly narrowing at the base to a long “winged” stalk. Leaves quickly lose this shape as they ascend the stem, becoming more lance-linear or elliptic with broadly winged stalks, and are reduced to stalkless bracts in the flower clusters. Basal leaves often wither away by flowering time and have very narrowly winged stalks, or lack wings altogether. Stems are single or multiple from the base, mostly erect, branched in the upper plant, rough-textured in the upper plant, and green or red.

Fruit:

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

Notes:

A species as much at home in open prairies as in open woods, Sky-blue Aster sets itself apart from other blue-violet asters with heart-shaped leaves in Minnesota by being more sun-tolerant than the rest. Of the others, Short's Aster (Symphyotrichum shortii) may be most similar, though its natural range is limited to just 3 southeastern counties. It has hairy phyllaries, leaves smooth on the upper surface and sparsely hairy on the lower, and are narrowly heart-shaped along much of the stem, where only the lowest leaves of Sky-blue Aster are heart-shaped. Of the other blue/violet asters with heart-shaped leaves, besides a preference for woodland or edge habitats, Blue Wood Aster (Symphyotrichum cordifolium), Drummond's Aster (S. drummondii), Lindley's Aster (S. ciliolatum), and Big-leaf Aster (Eurybia macrophylla) all have toothed leaves that are proportionately wider, where Sky-blue Aster leaves are mostly toothless. Arrowleaf Aster (S. urophyllum) also has toothed, heart-shaped leaves on the lower stem with winged stalks, but has white flowers.