"Coneflower [For Olaus (Olof) Johannes Rudbeck, 1630–1702, and Olaus (Olof) Olai Rudbeck, 1660–1740, father and son, professors at Uppsala University, predecessors of Linnaeus]
Annuals, biennials, or perennials, mostly 50–300 cm (mostly fibrous rooted or rhizomatous, sometimes taprooted). Stems 1–15+, erect, branched distally, glabrous or hairy, sometimes glaucous. Leaves basal and cauline; alternate; petiolate or sessile; blades elliptic, lanceolate, linear, oblanceolate, ovate, or spatulate, often pinnately lobed to 1–2-pinnatifid, ultimate margins entire, dentate, serrate, or coarsely toothed, faces glabrous or hairy, sometimes glaucous, sometimes gland-dotted. Heads radiate or discoid, borne singly or in ± corymbiform or paniculiform arrays. Involucres (early flowering) hemispheric to rotate, 15–30+ mm diam. Phyllaries persistent, 5–20 in 1–2(–3) series (narrowly triangular to lanceolate or narrowly elliptic, subequal, herbaceous, distally or throughout). Receptacles subspheric to ovoid, or conic to columnar, paleate (paleae mostly tan proximally, green to maroon distally, obovate, concave, each ± clasping a floret, apices acute to cuspidate or truncate to rounded, abaxial tips glabrous or hairy, sometimes gland-dotted, resin ducts 2–3, maroon, 1 medial and 1 near each margin; receptacles plus paleae and florets = discs, 8–80 × 5–30 mm). Ray florets 0 or 5–25+, neuter; corollas (spreading to drooping or reflexed) usually yellow to yellow-orange or bicolor (laminae often proximally maroon or each with a maroon splotch, distally yellow), sometimes wholly maroon (orangish red to maroon in R. graminifolia. Disc florets 50–800+, bisexual, fertile; corollas yellow, yellowish green, or brown-purple (often bicolor), tubes shorter than cylindric to funnelform throats, lobes 5, triangular. Cypselae (black) ± obpyramidal and 4-angled (often minutely cross rugose), faces glabrous, angles sometimes hairy; pappi 0, ± coroniform, or of 2–8+ unequal scales. x = 16, 18, 19.
Species 23 (23 in the flora): North America; introduced in Europe.
The species of Rudbeckia are distributed among three major clades or lineages. Although relationships among the lineages are not robustly resolved, the lineages are treated here as sections (as they have been traditionally). Rudbeckia hirta and sometimes other species of the genus are used in experimental studies relating to initiation of flowering and hairy root culture. Most species are rich sources of phytochemicals that may offer potential for pharmaceutical or other uses."
Urbatsch, Lowell E. and Patricia B. Cox. "Rudbeckia" in Flora of Northa America, Vol. 21, pp. 44-60, Oxford University Press, Inc., New York, NY. 2006.