Stems: White Wood Aster is an erect perennial that grows from 1 to 2-1/2 feet tall. Stems tend to have a slight zigzag to them and they can be spreading or sprawling. The stem within the floral array has dense very fine hair.
Leaves are large and thin, ovate-lanceolate in shape with heart shaped bases, sharp coarse teeth on the margins and a pointed tip that usually has a twist to it. If there is any leaf hair it will be sparse. The underside may have hair, particularly along the veins. Lower leaves are on long stalks. Upper leaves will be much smaller with short stalks, sometimes stalkless. The more basal leaves will drop by flowering time.
The floral array is a loose grouping of somewhat flat-topped branched clusters (Corymbs) branching from the top part of the stem. In a corymb the flower stalks are of different length so that the flower heads form a flat-topped cluster. Several long green bracts may appear among the flowers.
The flowers are about one inch wide composed of two types of florets: 5 to 10+ white ray florets that are pistillate and fertile, surrounding a central disc of 12 to 19+ tubular, bisexual, fertile, yellow disc florets that turn reddish at maturity. The tubes of the florets are unusually long and the lobes of the disc floret corolla are erect to spreading during flowering. The five stamens surround the style tightly and both protrude from the corolla. The rays of the ray florets can also have a lilac tinge of color. They also seem to be pointing in various directions. The phyllaries that surround the outside of the flower head number 25 to 30 in 4 to 5 series, unequal in size, are rounded to pointed in shape and are whitish with dark green tips. The inner series can have a purplish tinge. Flower head stalks and the phyllaries usually do not have any glandular hair.
Seeds are a brown dry cypsela, 2.6 to 3.8 mm long with 7 to 10 ribs and with a few fine reddish to cream colored bristles and hair for wind dispersion. Most Aster seeds normally need 30 to 60 days of cold stratification for germination.
Habitat: White Wood Aster grows from a creeping branched rhizome, which will form colonies. It prefers the drier, well drained soil of open woods in partial to full shade. Best to plant in an area where it can sprawl out as the flower clusters held above the leaves are quite showy.
Names: The species was originally named Aster divaricatus by Linnaeus in 1753, however, all the new world asters, formerly in the genus Aster, have now been reclassified, most into the genus Symphyotrichum, several, like this species, to Eurybia. The genus Eurybia is from two Greek words - eurys meaning 'wide' and baiso, meaning 'few', alluding to the few wide-spreading ray florets. The species name, divaricata, refers to the 'spreading' or 'growing in a straggling' habit. Asters in the Eurybia genus have disc florets with long tubes and funnelform to campanulate throats.
The author name for the new plant classification from 1995 - ‘G. L. Nesom’ is for Guy L. Nesom (b. 1945) American botanist who has published papers on the nomenclature of asters. He updated the work of the original author - '(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 Bigleaf Aster, E. macrophylla. Differences are that E. divaricata has white petals with little or no lilac color, fewer floret rays per flower head, and the leaves are only on the flowering stem, whereas E. macrophylla has more lilac color, 9 to 20 rays, and does have glandular hair. The Heart-leaved Aster, Symphyotrichum cordifolium, also have similar leaves, but the flower panicle is rounded, not flattened.
Above and Below: The flowers of White Wood Aster are composed of 5 to 10+ white ray florets surrounding a central disc of numerous yellow disc florets that turn reddish at maturity. The rays can also have a lilac tinge of color. They also seem to pointing in various directions. The phyllaries of the flower head (below left) have rounded to pointed in shape and are whitish with dark green tips. Note also the larger green bract on the stalk.
Below: 1st photo - The flower clusters of the floral array are somewhat flat-topped and not dense. 2nd photo - Lower leaves are large and thin, ovate-lanceolate in shape with heart shaped bases, coarse teeth on the margins, a pointed tip that usually has a twist to it. 3rd photo - The stem has a slight zigzag pattern.
Below: The seed head with individual seeds (cypselae) - both from the disc florets.
Below: 1st photo - the upper section of the plant. Stems can take on a darker reddish color late in the season. 2nd photo - Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Notes: White Wood Aster, formerly classified as Aster divaricatus, is not native to the State. It is native to the eastern United States and in Canada to Quebec and Ontario where it is considered rare and endangered. It was originally brought into the Garden by Eloise Butler in 1911 from Gillett's Nursery in Southwick, MA. She reported planting it on May 17th, 1911 along with a group of other species obtained from Gillett's. In her report to the Board of Park Commissioners in 1915, Eloise discussed the asters of the Garden. Her only comment on this species was that it had entirely died out. She replanted in April 1918 with plants from Gillett's. Martha Crone first planted it on Sept. 18, 1937, and again in 1945, however, it escaped being on Martha Crone's 1951 Garden Census, but is present again today as Susan Wilkins planted it in 2011 and 2012. Eurybia macrophylla (the Bigleaf or Large-leaved Aster) is the only species of Eurybia native to Minnesota.
Eloise wrote an essay on the Garden asters in 1915 for the Agassiz Association for publication in the Asa Gray Bulletin.
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"