Giant Goldenrod is a native erect perennial and is a common roadside Goldenrod.
Stems: It grows from 1 to 6 plus feet high. The stem is unbranched below the floral array, smooth throughout but within the floral array there may be sparse short stiff hair. In full sun stems can be reddish in color.
Leaves are all stem leaves, alternate, lance shaped with sharp teeth on the margins, tapering to a pointed tip and tapering to the stem; larger leaves with two noticeable veins parallel to the mid-rib, all 3 rising from the base. Upper stem leaves may be without teeth. Most leaves are sessile (stalkless). The lowest leaves usually wither by flowering time. Mid-stem leaves are the largest, 3 to 5 inches long, then decreasing in size into the floral array. The underside of the leaf may have hair on the main veins and nerves or can be otherwise smooth, but is much paler in color.
The floral array is a spreading pyramidal cluster of arrays at the top of the stem with the flowers on one side of each branch of the array; these branches tend to recurve backward (downward), particularly the lower branches of the array. The branches may have fine hair or be smooth.
Flowers: The yellow flower heads are bell shaped, less than 1/4 inch across, composed of two types of florets: 9 to 15 tiny pointed ray florets, with yellow rays, which are pistillate and fertile, and 7 to 12 disc florets with yellow corollas whose lips are pointed and erect to spreading during pollination. These are bisexual and fertile. The disc florets have 5 stamens with yellow filaments and anthers. The anthers surround and are appressed to the style. Anthers turn darker at pollen maturity. The thin phyllaries are greenish to yellow-green in color and these surround the flower head in 3 to 4 series of unequal size. The outer series lanceolate in shape with pointed tips and the inner series more linear with tips less pointed.
Seeds are dry cypselae, 1.3–1.5 mm long, with a fluffy whitish pappus for wind dispersal. The cypselae are tan and are of a shape called narrowly 'obconic' - that is like a narrow inverted cone. Seeds of Solidago usually require 60 days of cold stratification and light for germination.
Habitat: Giant Goldenrod is subject to some interesting galls (see below). The plant can form dense colonies from its creeping rhizomes and from self-seeding. It grows in roadsides, open fields, prairies where there is full to partial sun, moist to slightly dry conditions. This is the same habitat as Late Goldenrod, S. altissima and the two may frequently be found in the same area, although S. gigantea tends to bloom earlier. There may be some hybridization between plants growing in the same vicinity, which will tend to frustrate identification.
Names and varieties: The genus Solidago is from the Latin solido, to 'make whole' as the plants of this genus were known to "make whole". (see bottom of page). The species gigantea means 'large'. This species is one of the tallest native goldenrods. The author name for the plant classification - ‘Aiton’ is for William Aiton (1731-1793), Scottish botanist, who succeeded Phillip Miller as superintendent of the Chelsea Physic Garden and then became director of Kew Gardens, where he published Hortus Kewensis, the Garden’s catalogue of plants. Older synonyms for this species are Solidago serotina and Solidago pitcheri.
Comparison: Closely resembling this species is Late Goldenrod, S. altissima. That species has a similar height and root system, but the stems have fine hair throughout except sometimes at the base of the stem. S. altissima has fewer disc florets - 3 to 6 vs 7 to 12 and fewer ray florets - 5 to 13 vs 9 to 15. Its leaves have fewer teeth, the phyllaries tend to be more yellow, but it is also subject to the stem galls explained below.
Above: The floral array with its arching lower branches. 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.
Below: Detail of the flowers.
Below: 1st photo - a stem leaf, tapering on both ends, stalkless. 2nd photo - leaf underside showing fine hair on the mid-rib.
Below: Comparison of large mid-stem leaf and upper stem leaf.
Below: 1st photo - the phyllaries of the flower head. 2nd photo - Smooth stem, reddish when in full sun.
Goldenrod Galls: Late Goldenrod (Solidago altissima with two subspecies) and Giant Goldenrod (S. gigantea) are subject to three different types of stem galls caused by tiny insects that lay their eggs on the plants The larva from the hatched egg then eats its way into the stem. In two cases (ball gall and spindle gall) the plant then responds to this event by rapidly increasing cell growth around the intrusion, enveloping the larva in a woody protective sheathing that not only keeps the larva safe, but they have a ready-made food supply for the remainder of the summer and a home to overwinter in and emerge in spring as a new adult, unless a woodpecker finds them. In the case of the rosette gall (3rd photo below), the plant creates a dense growth of what looks like small leaves at the top of the plant after a larva hatches at the top of the stem. This rosette is caused by the plant stopping stem growth without stopping leaf production. In the case of the spindle gall (below- 2nd photo), the eggs are laid on an autumn leaf where they overwinter. In spring the hatched larva migrate from the dead leaf to a nearby stem, bore in for a home and the plant responds as indicated above. S. canadensis (two subspecies) is not known to be seriously affected by the galls.
John Muir wrote in 1911: Each species seems to know what kind of plant will respond to the irritation or stimulus of the puncture it makes and the eggs it lays, in forming a growth that not only answers for a nest and home but also provides food for the young." From his essay Mt. Hoffman and Lake Tenaya.
Below: 1st photo - The "ball" or "apple" gall. 2nd photo - The "spindle" gall. 3rd photo - The " numerous rosette" galls on Giant Goldenrod.
The insects that cause these galls are as follows: Ball gall - Goldenrod Gall Fly, Eurosta solidaginis; Spindle Gall - Goldenrod Gall Moth, Gnorimoschema gallaesolidaginis; Rosette Gall - Goldenrod Gall Midge, Rhopalomyia solidaginis. This gall only occurs on Late Goldenrod. Below: 1st photo - A larva of the Gall fly in the sectioned gall. Note the gall has a dense woody structure. 2nd photo - An example of a stem affected by all of them.
Notes: Giant Goldenrod is not indigenous to the Garden but it is to the local area. Eloise Butler first planted it in the Autumn of 1919 with plants she dug up near the Belt-line Bridge in Minneapolis (now called Highway 100). The name used in her day was Solidago serotina. She planted more in 1927 but Martha Crone did not list it on her 1951 Garden census. In 1987 Gardener Cary George wrote that it and another species not listed on Martha Crone's inventory were now in the Garden. He did not state that he planted it, just that it was there.
Subspecies: There are 18 species of Solidago known in the wild in Minnesota. Within Minnesota S. gigantea is found in all counties except eight in the SW farm belt. This is one of the most wide spread goldenrods, occurring in all the U.S. except Arizona, and in all the lower Canadian provinces except the Maritime. The other two main species, S. canadensis and S. altissima, are also very widespread.
Medicinal Lore: The genus Solidago has several species whose leaves and tops were used by natives for sickness of the stomach - usually a teaspoon of leaves to a cupful of boiling water. Hutchins (Ref. #12) mentions several other uses. Here in Minnesota, Frances Densmore (Ref.#5) reported that the Minnesota Chippewa used various species of Goldenrod, for treating cramps, fevers, colds, ulcers and boils. Mrs. Grieve (Ref. #7) reports on European use of various species.
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"