Aromatic Aster is a native perennial growing from 1 to 3-1/2 feet high on stiff slender stems that have weak bases so that the main stem frequently lies on the ground and profusely branches creating a bushy appearance. In late summer the main stems turn woody. Lower stems have coarse hair until they turn woody. Both the upper stems and the flower heads have glandular hairs that when crushed give off a balsam-like scent.
The leaves are alternate, narrowly oblong, up to 2 inches long and 1/2 inch wide, somewhat stiff, with coarse short hair and margins without teeth but with very fine hair. Tips are rounded to a point, bases are stalkless to slightly clasping. They are very dense on the stems but the upper leaves will be smaller than the lower stem leaves. Leaf color is yellowish to dark green. In this species leaf size and shape vary greatly.
The floral array consists of several to many flower heads in large clusters at the ends of branches.
Flowers: Each of the compound flowers is about 1 to 1-1/4 inches across and is composed of two types of florets. There are 25 to 35 blue to purple ray florets that are pistillate and fertile. These surround 30 to 40 tubular, bisexual, fertile disc florets that initially have yellow corollas which turn brown or reddish-purple toward maturity. The upper part of the corolla tube forms 5 triangular lobes. The disc florets open first along the outside circumference and progress toward the middle of the disc. Disc florets have 5 stamens, appressed around the single style. Anthers are also yellow until post pollination when they turn reddish purple. On the flower stalk are a number of spreading bracts that look like small leaves. These are linear and overlapping with pointed green spreading tips, usually glandular and aromatic, as are the flower stalks. The upper bracts grade into 4 to 5 series of smaller phyllaries around the outside of the flower head; these are also hairy and glandular.
Seed: Fertile flowers produce a dry, 7 to 10 nerved, brownish color cypsela, 2 to 2.5 mm long, that has tufts of light brown hair for wind distribution. Seeds are fairly heavy for aster seeds - 51,000 to the ounce and need warm soil for germination, but not cold stratification.
Habitat: Aromatic Aster grows from a fibrous and rhizomatous root system that forms a thick woody caudex. It prefers loamy soils with slightly dry conditions and full sun. It is not tolerant of soils that hold excessive moisture. In the wild it grows in prairies, pastures, roadsides, limestone bluffs and outcrops and is one of the latest to flower in our area. It can and will spread via stolons from the rhizomatous roots.
Names: The old name for this aster was Aster oblongifolius. All the new world asters, formerly in the genus Aster, have now been reclassified, most into the genus Symphyotrichum. The genus name is from the Greek symphysis, for 'junction', and 'trichos', for hair, all of which relates to a fine division by botanists of certain plant characteristics. The species, oblongifolium (and the earlier oblongifolius), is from the Latin words oblongus for 'longer than wide' and folia for 'leaf' and thus - oblong leaf, which this aster has. There is considerable variation in this species in leaf size and shape which once led to a number of varieties being designated. Those are no longer accepted. The author names for the plant classification are: ‘Nutt.’ refers to Thomas Nuttall (1786-1859) English botanist who lived and worked in America from 1808 to 1841. On his many expeditions he collected many species that had been originally collected by Louis and Clark but lost by them on their return journey. His work has been revised by ‘G. L. Nesom’ who is Guy L. Nesom (b. 1945) American botanist who has published papers on the nomenclature of asters.
Comparisons: There are a number of asters with blue-purple rays and yellow disk flowers. Check the following: Sky-blue aster, S. oolentangiense; Smooth Blue Aster, S. laeve; Red-stemmed Aster, S. puniceum; Silky Aster, S. sericeum; and New England Aster, S. novae-angliae. Those are all taller plants and do not sprawl like S. oblongifolium. Comparison photos are shown below for other asters with blue ray florets.
Above: Leaves on Aromatic Aster are small, about 2 inches long, shorter near the top. Note the fine marginal hair in the 2nd photo. 3rd photo - The main stems become woody as the plant matures.
Below: The bluish-purple ray florets number between 25 and 35. The center disk florets number 30 to 40. They have yellow corollas at first but as they begin opening from the outer edge first, they change color to a reddish-purple. Each corolla tube has 5 triangular lobes at the tip when open.
Below: 1st photo - The ray florets are pistillate - the styles can be seen in these photos along the base of the rays. The disc flowers are bisexual and fertile also. 2nd photo - The rhizomatous root system produces stolons as seen here, which spread underground to produce a colony of new plants.
Below: Around the flower head are a number of linear bracts with pointed tips. These have glandular hair and are aromatic when crushed. These grade into smaller phyllaries at the base of the flower head in 4 to 5 series.
Above and Below - A comparison of 4 blue flowered asters. Besides plant geometry, leaf shape and size, the diameter of the flower head, # of ray and disc florets (upper photo) and the shape of the phyllaries of the flower head (lower photo) help distinguish one species from another.
Notes: Aromatic Aster is not indigenous to the Garden. Eloise Butler first introduced it on Sept, 1, 1912 with plants sourced from "the forty" which is believed to be the 40 acres near the Minnesota River owned by her friend Clara Schutt. More were planted on Oct. 25, 1914 and in Sept. 1918, both from Fort Snelling. Martha Crone also planted 12 of the species in Sept. 1933 with plants sourced near Shakopee, MN; planted more in 1936, '44, and '45. It was still in the Garden at the time of her 1951 census, but not on any later census. Eloise Butler wrote in her 1915 report to the Board of Park Commissioners that "Aster oblongifolius is local on our prairies. It is pleasing by reason of the size, color and aromatic odor of the blossoms."
Much the same text was incorporated into an essay that was sent to The Gray Memorial Botanical Chapter, (Division D) of the Agassiz Association for publication in the Asa Gray Bulletin. Text here.
Distribution: Aromatic Aster is found only in the U.S. between the Rocky mountains and the Appalachians - absent in New England and the SE states. Within Minnesota its distribution is split between counties on the western side of the state and a group of counties in the SE from the metro down to Iowa. Asters are difficult to study. There are twenty-four species just of Symphyotrichum listed by the DNR and the U of M as being found in Minnesota, some with several subspecies.
Uses: Because of the tendency to bushiness and its tendency to spread via stolons, the plant can make a good ground cover - otherwise your planting will need to be thinned periodically. In a native plant landscape, pruning it back to half height in June will keep it from getting too top heavy. Like most asters, they are subject to lower stem rot if over-watered.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"