Rough Coneflower (Rudbeckia grandiflora var. grandiflora*) of the Aster (Asteraceae) family is an upright herbaceous perennial with multiple slender stems bearing yellow composite flowers. Genus name honors “Olof Rudbeck the Younger”, a Swedish botanist. Specific epithet is derived from Latin words for “big” and “flower”. Principal area of occurrence for the species is eastern Texas, eastern Oklahoma, western Louisiana and portions of Arkansas. In Arkansas, species occurrence is statewide except for the northern Ozark Plateaus and northern Mississippi Alluvial Plain. Occurrence of subject variety in Arkansas is primarily in the Arkansas Valley, Ouachita Mountains and western West Gulf Coastal Plain. Preferred habitats are mesic to dry soils of sunny prairies and open woodlands. Mature plants have a woody root-crown with numerous thin, ropy and fibrous roots. Previous year’s dead stems persist well into the new growth-year. Also known as Large Flower Coneflower.
Crowded clusters of basal leaves form a leafy mound across the root-crown. At maturity, the medium green basal leaves are to 13 inches long (including an 8-inch petiole) and 2½ inches wide. Blades are elliptic to ovate with a gradual taper from mid-leaf to an acute apex and a shorter taper from mid-leaf to a wedge-shaped (cuneate), fluted base. The fluted base continues as a central groove onto and along the petiole (stalk of leaf). Upper two-thirds of leaf margins (larger leaves) have forward-pointing (antrorse), shallow-serrate teeth. Primary veins consist of the midrib and a pair of secondary veins originating from the petiole and extending to leaf apex. Additionally, an out-board pair of secondary veins originates from near the base of the in-board pair of secondary veins. Secondary veins are arcuate as they parallel side margins toward leaf apex. Primary veins on the upper surface of the leaf are slightly recessed while primary veins on the underside of the leaf are prominently expressed and a slightly lighter green. Both sides of blades have short, stiff pubescence with longer hairs along primary veins of the abaxial side. Petioles also have dense pubescence, but the central groove is mostly hair-free.
As a stem emerges from the rootstock, its leaves (cauline leaves) extend above the growing stem-tip. The medium green stems have widely spaced, medium green, alternate, ascending leaves. The long-petiolate lower cauline leaves are elliptic with acuminate apices and fluted bases similar to those of basal leaves. Lower cauline leaves transition to smaller lanceolate leaves on shortening petioles and, near the flowerhead, to linear leaves that are sessile (without stalks). Lower cauline leaves grow to 12 inches long and 3 inches wide; size decreases distally as leaves become more linear. Upper one to several leaves may subtend an axillary branch which, as with the stem, terminates with a single flowerhead on a long peduncle (stalk of the flower). Margins of the smaller distal leaves are slightly wavy to entire. Mature stems (to 4 feet tall) are slender, erect and terete with closely spaced, longitudinal ridges bearing spreading (90⁰ to stem) stiff hairs proximally and strigose (stiff and appressed) hairs distally. Previous year’s dead stems are persistent (see Photo 1).
The June into July inflorescence consists of single composite flowerheads (to 5 inches wide) at the ends of straight, erect stems and branches. Flowerheads have 1) ray florets with elongate ligules (aka laminae) attached to an infertile ovary, 2) conic receptacles covered with tubular disk florets and 3) a flat-bottomed involucre of closely spaced, spreading, green phyllaries in several overlapping series (see Photo 13). The lanceolate phyllaries, to ¼ inch long and 1/16 inch wide at their broadened base, are glabrous on the inner side with dense strigose pubescence on the outer side, extending onto the peduncle. The central disk is covered with hundreds of tightly packed perfect (having stamens and pistils) disk florets.
At anthesis, flowerheads are composed of 12-18+ bright yellow, infertile (lacking stamens with an infertile ovary) ray florets in a single series surrounding a central reddish brown central disk. Early in flowering, ligules are in longitudinal rolls. At anthesis, ligules (to 2+ inches long and ½+ inch wide) are reflexed to drooping. The oblanceolate ligules have a rounded apex with a small notch (retuse apex) and a constricted base attached directly to an infertile ovary. Ligules are glabrous adaxially and have short fine (puberulent) pubescence abaxially.
The tightly packed disk florets, with 4 stubby floral lobes covering the throat before anthesis, are aligned in spirals from disk-apex to disk-base. Florets reach anthesis in sequential “bands” from disk base to its apex. Floral lobes recurve to open the throat. Receptive disk florets, about ⅛-inch long and 1/16 inch wide, have a purplish red exposed portion and a whitish green hidden portion. Florets are subtended by lanceolate, sharp tipped, white to green floral bracts (called paleae or chaff) that are folded lengthwise. Florets, have 5 stamens (filaments + anthers) and a pistil (ovary + style + stigma). The elongate, connate anthers become exserted as a ring above the corolla. Yellow pollen is released within the ring and pushed to the outside by the emerging reddish purplish style/stigma. Anthers shrink as the stigma divides (bifurcates) to expose an opposite pair of narrow-elongate stigmatic arms. The opposite arms recurve sharply to the point that their tips touch the style.
When all disk florets have passed anthesis, ray florets drop-off and the central disk become brown. Fertilized ovaries of disk florets produce ⅛-long dark gray, 4-sided, narrow-conic achenes (aka cypselae in Aster family) with a truncated top. Paleae persist while achenes drop-off.
Rough Coneflower may be a good choice for a naturalized area, prairie-like setting or as a specimen plant in a larger cottage garden. Plants do well in mostly sunny sites with various well-drained soil types. The perennial has slender, erect stems and branches with widely spaced leaves that are small distally so that showy flowerheads are well-exposed. Plants provide pollen to insects and seed for birds and small mammals. For smaller gardens, developing seedheads may need to be removed to prevent an overabundance of plants. Foliage is eaten by deer and rabbits.
Eight additional species of Rubeckcia occur in Arkansas – all with yellow composite flowerheads. Rough Coneflower can be distinguished by having 1) long erect stems and branches, 2) simple basal and lower cauline leaves with long petioles, 3) terminal flowerheads with recurved to drooping all-yellow ligules and 4) conic receptacles with widths that are about ⅓ the receptacles’ height.
Species of the genus previously addressed in Know Your Natives articles: Cut Leaf Coneflower (Rudbeckia laciniata var laciniata), Sweet Coneflower (Rudbeckia subtomentosa), and Brown-Eyed Susan (Rudbeckia triloba var. triloba).
- Two varieties of Rudbeckia grandiflora have been classified based largely on differences in stem pubescence. Stems of the R. grandiflora var. grandiflora has hairy stems on which hairs are spreading proximally and ascending distally. Stems of R. grandiflora var. alismifolia are glabrous or sparsely hairy proximally and hairy distally. Hairs of R. grandiflora var. alismifolia are ascending and half as long as those of R. grandiflora var. grandiflora.
Article and photographs by ANPS member Sid Vogelpohl
