Plants of the Eloise Butler Wildflower Garden

Sky Blue Aster is a native, erect, perennial aster of prairies and open woods, growing 2 to 3 feet high on stems that may or may not have hair and are green during the growth season.

Leaves are more toward the bottom of the stem, usually entire, thick and stiff; lower leaves often on an winged stalk. Basal leaves have a heart shaped base and a long petiole; upper leaves stalkless, lance shape, with a rounded base, but not clasping. All have a rough surface. Within the floral array, the leaves become linear, then shading to bracts near the flower heads, all stalkless. There is considerable variation in leaf shape.

The floral array is a branched cluster (a panicle), usually of many flowers, with stiff ascending branches that are leafy and with appressed bracts on the long flower stalks.

Flowers have two types of florets - an outer group of 13 to 20+ ray florets which have light blue to pinkish rays, 1/2 to 1-1/3 inches across the open head. These are pistillate and fertile. These surround the tubular central disc florets which have yellow corollas and number 20 to 25+. These are bisexual and fertile. The disc florets have 5 triangular lobes on the open throats and turn color toward reddish-purple at pollen maturity - typical of asters of this genus. Disc florets open from the edge of the central disc first then toward the center. The anthers of the disc floret stamens are yellow when the floret opens, and the five stamens tightly surround the style which has a branched appendage at its tip. Styles are exserted from the corolla when the flower opens. Flower stalk bracts are green, linear and usually appressed to the stalk. These grade into 4 to 6 series of phyllaries around the outside of the flowerhead. These too, are usually appressed but the outer series may be slightly spreading or even curled. They are generally whitish but have a short, dark green, diamond shape tip and are without hair.

Seed: Fertile flowers produce a 4 to 5 nerved dry purplish cypsela, 1.8 to 2 mm long, with white to creamy rose pappus attached for wind dispersion. Seeds germinate best in cool soil but no pre-treatment such as cold stratification, is necessary.

Varieties: Some references list two varieties for the species. Today, based on the work of Nesom, varieties of this species are not recognized by most authorities including the University of Minnesota Herbarium and Flora of North America.

Habitat: Sky Blue Aster grows best in mesic to dry sandy to loamy soils in full to partial sun. It is found in prairies, bluffs, dunes, open wood savannas. Excess water is detrimental. It grows from a short rhizomatous root system or from woody caudices, which form clumps, not spreading colonies.

Names: That strange species name, oolentangiense, refers to the Oolentangy River in Ohio where Riddell, who named the plant, found the species in 1835. Its former scientific name was Aster oolentangiensis Riddell. Another older name, but the most descriptive, is Aster azureus, which species name means 'sky-blue'. However, all the new world asters, formerly in the genus Aster, have now been reclassified, most into the genus Symphyotrichum. That genus name is from the Greek symphysis, for 'junction', and 'trichos', for hair and, while obscure, it was first applied by Christian Gottfried Daniel Nees von Esenbeck in the 1800s in describing the type aster for the genus.

The author names for the plant classification are as follows: The first to publish was ‘Riddell,' which refers to John Leonard Riddell, (1807-1865), American chemistry professor, botanist, writer, and medical doctor. He was born in Massachusetts, but most of his botanical observations were in the central states from Ohio southward. His important work was a “Synopsis of the Flora of the Western States” defined at the time as the territory from the Allegheny mountains to the Platte River in Missouri Territory. It was in great part a compilation. He later published Catalogus Florae Ludovicianae. He served as Adjunct Professor of Chemistry and Lecturer on Botany in the Cincinnati Medical College where he also received his M.D. and he later became chair of the Chemistry Dept. in the Medical College of Louisiana (which then became the University of Louisiana), which position he held until his death. It was there he invented the binocular microscope. The plant genus Riddellia was named for him. His descriptions for this species were updated by ‘G. L. Nesom’ who is Guy L. Nesom (b. 1945) American botanist who has published papers on the nomenclature of asters.

For comparison, a similar blue aster flower grows in the upland Garden -- the Smooth Blue Aster, Symphyotrichum laeve; it has different leaves that are stalkless or clasp the stem and the flowerhead phyllaries are more green with the tips more an elongated diamond to linear. See comparison photo below.