Flat-topped Aster is a native erect perennial growing on stems that are 3 to 6 feet high, reddish color lower and green to reddish-green in and near the inflorescence. Stems may be smooth or slightly hairy.
Leaves are lance shaped, 4 to 6 times longer than wide, entire, stalkless on the uppers, short stalks on lower leaves, tapering at both ends. Leaves on the mid and upper part of the stem are more crowded than below and reduce in size toward the inflorescence. Leaves of this variety are densely hairy on the underside.
The floral array is a flat-topped branched cluster; the entire array is composed of a number of smaller open clusters (which are known as corymbiform arrays), each array on its own stalk, branching and sub-branching from the main stem. In a corymb the flower stalks are of different length so that the flowers form a flat-topped cluster. Stems and flower stalks within the array have fine hair.
Flowers: The small flowerheads (1/2 to 3/4 inch wide) have two types of florets: White ray florets of 2 to 10+ rays which are pistillate and fertile, surrounding a central disc of 5 to 26+ disc florets which are bisexual and fertile.Disc florets are tubular with five anthers appressed against the style. The 5 lobes of the disc corollas are light yellow with outward turned and reflexed lips. Unlike asters in the Symphyotrichum genus, these do not turn reddish-purple at maturity. The outer circumference of the flower heads have 3 to 4 series of phyllaries that are light green, linear, tips tapering to a point and somewhat overlapping. In this species, the midvein of the phyllary is not swollen. The phyllaries are of unequal length with faces covered with very short stiff hair.
Seeds: Fertile flowers produce a 4 to 6 ribbed dry cypsela covered with stiff short hairs, that has 4 series of bristles attached for wind dispersion. The outer bristles are linear and pointed, whitish, while the 3 inner series are white to tan with barbed tips. These 4 whorls of bristles are distinctive of the Doellingeria genus. Seeds require at least 60 days of cold stratification for germination.
Varieties: Two varieties are recognized: var. pubens, described here and var. umbellata where the underside of the leaves are sparsely hairy. Both are native to Minnesota, but the DNR county plant surveys do not distinguish between them.
Habitat: The plant does well in moist soil and full sun and is one of the earliest blooming asters in the Woodland Garden along the wetland trail. It also does well in the somewhat drier upland savanna habitat. It grows from a rhizomatous root system which can produce a short woody crown.
Names: Formerly classified as Aster umbellatus, Flat-topped Aster, like most other North American asters, has recently been reclassified by botanists into another genera. A large number went to Symphyotrichum but this one and two others are now in Doellingeria. These latter are, most generally speaking, the white flat-top asters. The genus name Doellingeria is an honorary for Ignatz Doellinger (1770-1841), German doctor, anatomist and physiologist, professor at Bamberg and then Munich. One of his students was Louis Agassiz. The species name, umbellata, refers to the umbrella-like flower heads. The variety pubens refers to the dense hair on the leaf underside. The author names for the plant classification are: "Mill." is for Philip Miller, Scottish botanist (1691-1771) who was chief gardener at the Chelsea Physic Garden and wrote "The Gardener's Dictionary". His work was updated by 'Nees' who is Christian Gottfried Daniel Nees von Esenbeck (1778-1858) German botanist who described around 7000 plant species, authored a number of monographs and was a Professor at Erlangen, Bonn and Breslau.
Comparison: Flat-topped Aster with a flat-topped umbrella like cluster of white flowers is not confused with any other in Minnesota. The two other similar species, D. infirma and D. sericocarpoides are found near the east and gulf coasts.
Above and below: The floral array. 2nd photo below - in the bud stage. The array structure is composed of what are known as corymbiform arrays. In a corymb array the flower stalks are of different length so that the flowers form a flat-topped cluster.
Below: 1st photo - One of the individual corymbs that make up the flat-top. 2nd photo - Details of the disc florets - yellow corolla with lips outward turned and reflexed.
Below: - Details of the phyllaries - light green, linear and overlapping. Note fine hair on stalks,, phyllaries and leaf undersides.
Below: 1st photo - The long lance-shape leaf, base tapers to the stem on upper leaves. Stem usually reddish or with reddish tints. 2nd photo - The underside of the leaf of var. pubens has fine hair all over creating a pale color and longer hair on the mid-rib and veins. Note also the fine hair on leaf margins.
Below: Stem section
Below: 1st photo - The seed heads showing the whitish outer bristles of the formed seeds. 2nd photo - Individual seeds.
Notes: Flat-topped Aster is indigenous to the Garden Area, Eloise Butler cataloged it on Sept. 6, 1907. It was listed on Martha Crone's 1951 inventory of plants in the Garden at that time and was listed on all subsequent census. Neither Eloise or Martha ever recorded planting it, thus it is quite hardy in the wetland. However, for it to be present in the Upland Garden, it would have to have been planted by someone, or by wind dispersion. It is native to most of Minnesota except the drier counties of the West and SW. In North America it has a range limited to 9 states of the Upper Midwest centered around Minnesota and in Canada it is limited to the Provinces of Alberta eastward to Quebec. This is the only species of Doellingeria found in Minnesota or in the central North American Continent.
Eloise Butler wrote about the asters in the Garden in her 1915 report to the Board of Park Commissioners. Of this species she said: "Aster umbellatus is highly esteemed because of its tallness, its ample flat-topped flower clusters of mingled gray and yellow that set off and harmonize with the luxuriant masses of Joe-Pye weed."
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"