Symphyotrichum oolentangiense (Sky-blue Aster)

Plant Info
Also known as: Azure Aster
Family:Asteraceae (Aster)
Life cycle:perennial
Habitat:part shade, sun; dry sandy or rocky soil; prairies, savannas, open woods, woodland edges
Bloom season:August - October
Plant height:12 to 40 inches
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 7+petals Cluster type: panicle

[photo of flowers] 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.

[photo of bracts (phyllaries)] 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: Leaf attachment: alternate Leaf type: simple

[photo of leaves] 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 type: seed with plume

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


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.

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More photos

Photos taken at Wild River State Park, Chisago County, and Long Lake Regional Park, Ramsey County. Photos courtesy Peter M. Dziuk taken in a private garden in Anoka County.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Ken - Sherburne County
on: 2009-08-20 21:03:35

I am having two acres of prairie restored. This seems to be the aster we are seeing in bloom now (midAugust). When it came up the plant was a very dark blackish green. The upper part was mostly stiff stems with few leaves. At first we thought it might be a weed, but fortunately did not pull it.

Posted by: Alan - Lake Crystal, MN
on: 2014-09-11 18:56:20

I'm trying to identifed every wildflower on my 6 acre country homesite. Its amazing how many flowers are similar. I think this Sky Blue Aster is the correct one as the centers are begining tp turn red.

Posted by: Linda Johnston - Twin cities
on: 2019-09-17 19:42:51

My labeled sky blue asters flowers are white. Why ? Or did the nursery mislabel?

Posted by: K. Chayka
on: 2019-09-18 06:40:38

Linda, it is not uncommon for a species that normally has non-white flowers to produce a plant with white. It's a natural variation that happens with many different species. If you're unsure you have the correct species you could post some images on the Minnesota Wildflowers Facebook page.

Posted by: Karen Watkins - North Branch
on: 2020-08-27 13:43:20

I found this plant in the near the North Branch Community garden behind the public library. Such a beautiful shade of blue.

Posted by: Molly Stoddard - Fergus Falls, Otter Tail County
on: 2020-09-04 13:23:22

at One Mile Lake Prairie and at the Prairie Wetlands Learning Center

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