Sweet Black-eyed Susan is an erect perennial forb, growing from 2 to 6+ feet high on stems that branch occasionally. Plants will send up multiple stems from the root crown. Stems are ridged, green with purple lines and are densely hairy with outward and upward pointing hairs (antrorse hair).
The leaves differ in shape between the basal leaves and the stem leaves. Basal leaves are deeply 3 to 5 lobed, each lobe with dentate edges, and the leaf on a long stalk. The stem leaves are ovate to elliptic and not lobed with shorter stalks and stalkless on the very upper parts of the stem. Stem leaves have some coarse teeth on the edge, 3 to 5 main parallel veins and are densely covered with fine hair on both surfaces, the upper surface usually gland-dotted. The tips are tapered to a point, the bases more abruptly tapered to the stalk.
The floral array consists of several to many stalked composite flower heads in branched clusters atop the stem.
The flowers have a central hemispherical disc, flattened on top, composed of 200 to 400 bisexual and fertile disc florets that have corolla tubes that are yellowish-green in the lower half and brownish-purple in the upper half. The tubes have five triangular lobes at the tip and the single style is branched at the tip. The five stamens surround the style. The central disc is surrounded by 10 to 16 ray florets, neuter as to sex. These have yellow to yellow-orange rays that may reflex a bit near the tips but are seldom drooping. Around the outside of the flower head are 2 to 3 series of phyllaries (floral bracts) that are hairy and gland-dotted. They are narrowly lance shaped with pointed tips and spreading but not reflexed.
Seed: Fertile disc florets produce a dry, dark, 4-angled cypsela, somewhat pyramid shaped, 2 to 3.5 mm long, that does not have any fluffy pappus. Dispersion is by scattering from the dry seed head. Seeds require at least 30 days of cold stratification for germination.
Habitat: Sweet Black-eyed Susan prefers moist to mesic soils, prefers full sun but will flower in partial shade although the plant will not be as robust. In the wild it is found in woodland openings, wet prairies and stream banks. The root system is rhizomatous with stout rhizomes. Plants do not spread but the base continually enlarges and the plants can achieve great bulk. Roots of mature plants are frequently 2+ feet deep. Divide and transplant in early spring. This species is frequently grown as an ornamental and because of its height it should be used as a background plant. Many varieties of bees will frequent the flowers.
Names: The genus Rudbeckia, is named after the Swedish father and son, - O. J. and O. O. Rudbeck, who were professors of botany and predecessors of Linnaeus. The species name, subtomentosa, is derived from 'sub' meaning 'mostly or almost' and tomentosa, meaning densely hairy. The meaning therefore says this species is densely hairy but not as much as much as some other Rudbeckia species. The author name for the plant classification, ‘Pursh’ is for Frederick Traugott Pursh (1774-1820) German-American botanist who wrote A Systematic Arrangement and Description of the Plants of North America, and was the botanist who catalogued and described the plants brought back by the exploring expedition of Lewis and Clark.
Comparisons: Three others of the Rudbeckia genus must be mentioned: Black-eyed Susan, R. hirta, Orange Coneflower, R. fulgida, and Thin-leaved Coneflower, R. triloba. R. hirta is shorter, has more yellow ray flowers, a flattened dome of disc florets, and has a single flower, not a cluster. R. triloba has the same height, but the stem-leaves are also lobed and the flower heads have fewer ray flowers that are broader with more rounded tips. R. fulgida is a shorter plant, with broadly ovate to elliptic leaves that are not lobed, either basal or stem, the ray florets are more orange-yellow.
Above: The floral array consists of several to many stalked composite flower heads in branched clusters atop the stem. 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: The hemispherical disc is flattened on top. The upper parts of the corolla of the fertile disc florets is a dark brownish-purple. The yellow ray florets are neuter.
Below: 1st photo - The phyllaries are hairy, gland-dotted and in 2 to 3 series - not reflexed when the flower opens. 2nd photo - Stem leaves are more oval with some coarse teeth on the margins, larger ones stalked, very upper not.
Below: 1st photo - Leaf surfaces have fine hair and the under side can have very dense fine hair. 2nd photo - The lower leaves are stalked and deeply 3 to 5 lobed with dentate edges. Upper stem leaf shown next to it for comparison.
Below: Seeds (shown amidst the fluff) are dark, dry 4 sided cypselae, somewhat of a narrow pyramid in shape, without any fluffy pappus.
Below: 1st photo - The root system is rhizomatous but not spreading - forming a large clump instead. 2nd photo - The stems are ridged with many fine upward and outward pointing hair and purplish longitudinal lines. 3rd photo - A tapering upper stem leaf.
Notes: Sweet-black-eyed Susan was introduced to the Eloise Butler Wildflower Garden by Eloise Butler on Sept. 28, 1921 with plants from Dreer’s Nursery Philadelphia. As explained below there is some question as to whether it is native to Minnesota, but it is definitely native to Iowa and Wisconsin. In North America it is found from Iowa south to Kansas, Oklahoma and Texas, in all the states bordering the Mississippi River plus Michigan, North Carolina, New York, Road Island and Connecticut.
Four species of Rudbeckia are considered native to Minnesota: R. laciniata, Green-headed (or Tall) Coneflower; R. hirta, Black-eyed Susan; R. triloba, Three-leaved (or Thin-leaved) Coneflower; and R. subtomentosa, Sweet Coneflower (Sweet Black-eyed Susan), although the latter is considered either an introduction or an extension of its normal range from Iowa and southern Wisconsin, as there is only one known population in the wild, in Mower County. The nursery trade has produced cultivars of Green-headed Coneflower, known commercially as Golden-glow, which occasionally escapes from cultivation.
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"