89. Rudbeckia L. (coneflower)
Plants annual or
more commonly perennial herbs, mostly fibrous-rooted, less commonly with
rhizomes or taproots. Stems erect or ascending, unbranched or few- to several-branched
toward the tip, with several longitudinal lines or ridges, glabrous or
variously hairy, slightly roughened to the touch. Leaves basal and alternate,
the basal and lower stem leaves long-petiolate (except in R. missouriensis),
the petioles progressively shorter up the stem, the upper stem leaves usually
sessile or nearly so, the bases usually moderately expanded and more or less
clasping or wrapping around the stem. Leaf blades simple, sometimes deeply
ternately or pinnately lobed, those of the basal leaves usually ovate to
elliptic-ovate (oblanceolate in R. missouriensis), those of the stem
leaves variously linear to broadly ovate, tapered or rounded at the base,
mostly angled or tapered to a sharply pointed tip, the margins otherwise entire
or toothed, the surfaces glabrous or more commonly hairy (usually roughened),
sometimes with sessile or impressed glands, with 1–5(–7) main veins.
Inflorescences of solitary terminal heads, these sometimes appearing as loose,
open clusters or leafy panicles, the heads mostly with relatively long stalks,
these often with 1 or 2 bracts similar to the involucral bracts at or near the
tip. Heads radiate (discoid elsewhere). Involucre broadly more or less
saucer-shaped, the bracts in 1 or 2 subequal, overlapping series. Involucral
bracts 5–25, linear to narrowly lanceolate or narrowly ovate, spreading to
reflexed, green, the margins and outer (usually also the inner) surface
roughened-hairy, not glandular, the midnerve inconspicuous. Receptacle nearly
spherical to conical or less commonly somewhat cylindrical, often elongating
somewhat as the fruits mature, with chaffy bracts subtending the disc florets
(also the ray florets in R. amplexicaulis), these shorter than to
slightly longer than the disc florets (including the corolla), concave and
wrapped around the florets, truncate or rounded to angled or tapered to a
sharply pointed tip, this unawned or with a soft, bristlelike awn, the apical
portion green to dark purple, persistent at fruiting. Ray florets 5–21, sterile
(lacking stamens and style at flowering and with an ovary that is shorter and
thinner than those of the disc florets, not developing into a fruit), the
corolla showy, relatively slender to somewhat broadened, spreading to drooping
at flowering, yellow to orangish yellow, sometimes strongly reddish- or
orangish-tinged toward the base, not persistent at fruiting. Disc florets 50 to
numerous (more than 200), perfect, the corolla yellow, yellowish green, purple,
or purplish brown, not thickened at the base, not persistent at fruiting. Style
branches with the sterile tip somewhat elongate, tapered, and bluntly or
sharply pointed. Pappus of the disc florets absent, a low rim or crown, or of 2–6
minute, unequal scales, usually persistent at fruiting. Fruits narrowly
wedge-shaped to nearly oblong in outline, usually strongly 4-angled in
cross-section, each face with several faint to more prominent but slender
lines, grooves, or ribs, the angles sometimes very narrowly winged, the surface
glabrous, brown to black, sometimes somewhat shiny. About 23 species, U.S.,
Canada; introduced in Europe.
A number of
species of Rudbeckia are cultivated as ornamentals in gardens (Dress,
1961). A few species, such as R. hirta, also are sold as cut flowers.
Native Americans used several species both topically and internally for a
variety of ailments ranging from sores and burns to worms, snakebites, kidney
disease, and heart problems. The foliage and stems of R. laciniata also
were cooked and eaten by some tribes (Moerman, 1998). Species of Rudbeckia,
especially R. laciniata, have been implicated in livestock poisoning.
The active agents apparently belong to a group of sesquiterpene lactones.
Burrows and Tyrl (2001) noted that experimental efforts to reproduce symptoms in
pigs and sheep first reported anecdotally were only partially successful, with
depression, loss of appetite, loss of coordination, and increased respiration
apparently passing away relatively quickly without long-term effects. They also
noted that because the plants have a strongly disagreeable flavor, livestock
avoid eating them unless no alternative food plants are present.
Abrahamson and
McCrea (1977) researched different patterns of absorption and reflectance of
light in the ultraviolet portion of the spectrum on the corollas of R.
hirta, R. laciniata, and R. triloba. A number of insects (such as
bees) are able to see light in the ultraviolet portion of the spectrum, which
is invisible to humans. The ultraviolet corolla patterns, which have been
studied in a variety of plants, act as visual cues to attract appropriate
pollinators.