Stems: Bigleaf Aster is a native erect perennial with stems from 1 to 4 feet high. They begin green in color but pickup a reddish-purplish tinge. First a basal rosette of leaves appears and then the stem. Not all rosettes will form a flowering stem each year, sometimes very few as many are sterile. The lower stem has slight angles but is usually without hair, the upper stem where branching can occur will usually have fine hair, particularly into the floral array.
Leaves: The plant is identified by its many large broadly ovate, coarse, thick and firm basal leaves (4 to 8 inches wide) with heart shaped bases growing on long hairy stalks, some hair is glandular. The leaf underside will usually have hair, especially on the veins. Leaf margins on the larger leaves will have sawtooth edges. After the flowering stem grows these basal leaves may die back. The alternate lower stem leaves will be smaller, more oval but still stalked and the stalks will have wings at the stem. Leaves become stalkless near the top of the stem.
The floral array is a corymbiform array composed of individual corymbs (In a corymb the flower stalks are of different length so that the flower heads form a flat-topped cluster). Each flowerhead is about 1-1/4 inch wide (although some may be smaller).
Flowers: Flower heads have two types of florets - a ring of outer ray florets that number from 9 to 20 and can have white to lavender-blue rays but most often the latter. These are pistillate (Female) and fertile. In this species they sometimes have the appearance of pointing in all directions. These surround 20 to 40 bisexual fertile disc florets that have long corolla tubes of cream to light yellow color that turn reddish-purplish at maturity. The disc floret corolla throat is very short and has 5 pointed erect to spreading tips. The 5 stamens tightly surround the style which has yellow appendages at its tip. Both style and stamens are greatly exserted from the disc corolla when the floret opens. Flower head stalks and stalks of the floral array have short glandular hairs. Under the rays, the flower head has 5 to 6 series of 32 to 35 overlapping, tight (appressed) green phyllaries, often purple tinged and with green blunt-to-slightly-pointed tips and margins that are whitish or slightly translucent. Under each flower cluster there is usually a single leafy green oblong stalkless bract.
Seeds are a dry, brown, 7 to 12 ribbed cypsela, 2.6 to 4.5 mm long, with tawny bristly pappus attached for wind dispersion. Cypselae are shaped like an elongated narrow cone (iconic). Seeds require 60 days of cold stratification for germination.
Habitat: Bigleaf Aster grows from a creeping rhizomatous root system whose offshoots will form dense colonies of the plant. It grows best in partial sun in well drained soil of wet-mesic to dry conditions. It will also grow in the full shade of open woods but in deep shade it may not produce a flowering stem and instead produces a colony of leaves. It is the earliest blooming aster in the Upland Garden.
Names: Aster is from the Greek for "a star" referring the appearance of the flower head on all Asters. The species name macrophyllus and macrophylla is the combination of macros for large and phyllos for leaf giving us the common name of "large-leaved." All the new world asters, formerly in the genus Aster, have now been reclassified, most into the genus Symphyotrichum; several, such as this species, into the genus Eurybia. That word comes from two Greek words, eurys, for "wide" and baios for "few", both together thought to be referring to the small number of flower rays, that are also somewhat wide. Asters in the Eurybia genus have cordate leaves (heart-shaped bases), disc florets with long tubes and funnelform to campanulate throats. The author name for the plant classification - ‘Cass’, is for Henri Cassini (1781 - 1832) French botanist, specialist in sunflowers, who wrote many papers and named many plants in the Asteraceae family. He amended the earlier work of '(L.)' which refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: The most likely species to confuse with this one is it's sister in the Eurybia genus, the White Wood Aster, E. divaricata, or the Heart-leaved Aster, Symphyotrichum cordifolium. Differences are that E. divaricata has white petals with little or no lilac color, fewer rays per flower head, and the leaves are only on the flowering stem - none basal. S. cordifolium has a rounded shape flower cluster but similar heart-shaped leaves. Comparison photos are shown below for other asters with blue ray florets.
Above: A large and small specimen of Bigleaf Aster. 3rd photo - The phyllaries of the flower head are in 5 to 6 series.
Below: 1st photo - The floral array is a group of corymbs - arrays that appear more-or-less flat-topped as the flower heads develop. 2nd photo - The flower head has 9-20 ray florets, usually lavender-blue and 20 to 40 disc florets.
Below: 1st photo - The disc florets are bisexual with yellow corollas that turn reddish-purple at maturity. Note the long disc floret tubes and the yellow appendages on the styles. 2nd photo - These flower heads have ray florets more white in color.
Below: The large lower leaf with long stalk and heart-shaped base. Note the wing at the end of the stalk in the 2nd photo.
Below: 1st photo - The upper leaves are stalkless. 2nd photo - The underside of the larger leaves have fine white hair on the veins and ribs.
Below: The seed head, left, showing the tawny bristly pappus of the cypselae, and, 2nd photo, individual cypselae.
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 (photo above) and the shape of the phyllaries of the flower head (photo below) help distinguish one species from another.
Notes: Bigleaf Aster is not indigenous to the Garden area. Eloise Butler introduced the plant to the Garden in 1912, '13, '14 and '17. Her first plants in 1912 came from Horsford's Nursery, Charlotte Vermont. In 1913 and '14 she sourced them from Pine Coolee near St. Paul; in 1917 and '18 from Mahtomedi MN; and also from Lutzen in '18. Martha Crone planted it in 1945 and Bigleaf aster was listed on her 1951 inventory of plants in the Garden at that time. Susan Wilkins planted more in 2009. It is native to Minnesota in counties in the NE 2/3rds of the state extending southward through the metro area, and also to a few counties in the SE corner of the state. Its westward range in the United States does not extend past Minnesota, nor westward of Manitoba in Canada. Eurybia macrophylla is the only species of Eurybia native to Minnesota.
Eloise Butler wrote about the asters in the Garden in her 1915 report to the Board of Park Commissioners. Of this species she said: "The large, rough basal leaves of Aster macrophyllus give the plant a marked individuality. The flowers, though pale in color, attract attention by their size and abundance. This aster is local in the vicinity of St. Paul and takes kindly to cultivation."
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.
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"