1. Rudbeckia amplexicaulis Vahl (clasping coneflower)
Dracopis
amplexicaulis (Vahl)
Cass.
Pl. 276 b; Map
1217
Plants annual,
with taproots. Stems 20–70(–90) cm long, glabrous, occasionally slightly
glaucous. Leaves all unlobed, all (except sometimes the basal ones) strongly
cordate at the base and clasping the stem, the margins entire or bluntly and
usually finely toothed, the surfaces glabrous, smooth, usually somewhat
glaucous, appearing bluish green when fresh. Basal and lowermost stem leaves
usually absent at flowering, long-petiolate to nearly sessile, the blade 2–15
cm long, 6–15 mm wide, oblanceolate to oblong-oblanceolate, rounded to sharply
pointed at the tip. Median and upper stem leaves sessile, the blade 1–10 cm
long, 8–40 mm wide, progressively shorter and broader, oblong-ovate to
oblong-obovate, ovate or heart-shaped, tapered to a sharply pointed tip.
Inflorescences mostly appearing as loose, open clusters of heads, sometimes of
solitary heads. Involucral bracts 7–12, 3–10 mm long, linear to lanceolate,
glabrous. Receptacle 10–30 mm long, 8–15 mm in diameter, hemispherical to
somewhat ovoid at the start of flowering, then elongating and becoming ovoid to
conical. Chaffy bracts subtending the ray and disc florets, shorter than the
disc florets, broadly angled or abruptly short-tapered to a usually sharply
pointed tip, the outer surface glabrous, the margins with a fringe of minute,
spreading hairs. Ray florets 6–10(–12), the corolla 12–30 mm long, relatively
broad, strongly reflexed at flowering, yellow, sometimes strongly reddish- or
orangish-tinged toward the base, the outer surface moderately to densely
short-hairy. Disc florets numerous, the corolla 2.5–3.5 mm long, greenish
yellow to yellow toward the base, dark purple to brownish purple toward the
tip, the lobes usually strongly curled downward at flowering. Stigma lobes elongate
and more or less sharply pointed at the tip. Pappus absent or occasionally a
minute rim or crown. Fruits 1.8–2.5 mm long. 2n=32. May–July.
Uncommon in
Jasper and Newton Counties, also introduced there and elsewhere in western
Missouri as well as the city of St. Louis (southern [mostly southeastern] U.S.
north to Kansas and Missouri; introduced sporadically farther north). Upland
prairies and glades; also edges of crop fields, railroads, roadsides, and open,
disturbed areas.
Steyermark (1963)
treated R. amplexicaulis (as Dracopis) as native in Missouri, and
the oldest specimens, from Jasper and Newton Counties (collected by E. J.
Palmer in 1909), apparently were collected from native plant communities. The
species also grows natively in adjacent portions of Oklahoma and Kansas.
However, most of the historical materials and all of the more recent
collections undoubtedly represent introduced populations. Clasping coneflower
is cultivated as an ornamental in gardens and can escape to form extensive
populations in disturbed habitats. It also has been planted along some highways
as a component of wildflower seed mixes for so-called roadside beautification
projects.
The
classification of this species remains somewhat controversial. Steyermark (1963)
and most earlier authors maintained it as the only species of Dracopis
Cass. This interpretation was supported by the phylogenetic analysis of
morphological and anatomical characters in the various coneflower genera of Cox
and Urbatsch (1990), who concluded that the genus is a relative of Ratibida.
Molecular phylogenetic studies of the coneflower genera involving restriction
site variation within the chloroplast genome was inconclusive but weakly
favored a similar interpretation (Urbatsch and Jansen, 1995). However, an
expanded molecular study that integrated the earlier chloroplast genomic data
with nuclear sequence data resolved Dracopis as a distinct lineage
nested within Rudbeckia (Urbatsch et al., 2000). Urbatsch and his
colleagues favored a classification in which Dracopis is treated as one
of three subgenera within Rudbeckia. This classification is followed in
the present treatment.