11. Helianthus pauciflorus Nutt. (stiff sunflower, prairie sunflower)
H. rigidus Desf.
H.
laetiflorus Pers. var. rigidus
(Desf.) Fernald
Pl. 282 i, j;
Map 1198
Plants perennial
herbs, with relatively long-creeping, thick, branched rhizomes, often occurring
as colonies of stems. Stems usually appearing solitary, 30–150(–200) cm long,
sparsely to densely roughened-pubescent with short, loosely ascending to more
or less spreading, short, stiff, pustular-based hairs. Leaves well developed
along the stem (usually with 5–15 nodes), all or mostly opposite, sessile or
with a poorly differentiated, winged petiole to about 1 cm long. Leaf blades
4–25 cm long, 2–6 cm wide, relatively thick-textured, lanceolate to
elliptic-ovate or those of the uppermost leaves sometimes narrowly oblanceolate
(mostly [2.0–]2.5–8.0 times as long as wide), flat, not folded longitudinally,
tapered at the base, tapered gradually to a sharply pointed tip or angled more
abruptly to a bluntly or sharply pointed tip, the margins finely toothed to
nearly entire, flat, the surfaces strongly roughened with moderate to dense,
minute, stout, pustular-based hairs, also with sparse to moderate, sessile,
yellow glands, with 3 main veins, the lateral pair branching from the midnerve
well above the base of the blade, arching upward. Inflorescences of solitary
terminal heads or more commonly appearing as open clusters or open panicles.
Involucre 12–20 mm long, 15–25 mm in diameter, shorter than the tips of the
disc corollas, the bracts in 3 or 4 noticeably unequal, overlapping series,
elliptic to oblong-ovate, narrowed to a bluntly or sharply pointed, tightly
appressed tip, the margins with a fringe of short, spreading hairs, the outer
surface glabrous or sparsely hairy but usually lacking glands. Receptacle
convex, the chaffy bracts 8–10 mm long, narrowly oblong to narrowly
oblong-oblanceolate, angled or short-tapered to a sharply pointed, green or
purplish-tinged, minutely hairy tip, the outer surface also usually minutely
hairy above the midpoint. Ray florets 10–21, the corolla 2.0–3.5 cm long,
glabrous or the outer surface microscopically roughened. Disc florets with the
corolla 6.0–7.5 mm long, the corollas reddish brown to dark purple (at least
the lobes and the upper portion of the tube). Pappus of 2 scales 4–5 mm long,
these lanceolate to narrowly triangular, tapered to a sharply pointed, often
minutely awnlike tip, also usually with 2–8 additional minute, oblong scales
0.3–2.0 mm long. Fruits 5–6 mm long, narrowly wedge-shaped to narrowly obovate,
flattened but more or less 4-angled in cross-section, the surface often with
fine, ascending hairs when young but usually glabrous or nearly so at maturity,
uniformly dark brown to black or sometimes with lighter brown streaks or
mottling. 2n=102. August–October.
Scattered in the
Glaciated and Unglaciated Plains Divisions, uncommon in the Ozarks and
Mississippi Lowlands (Montana to New Mexico east to Maine and Georgia; Canada).
Upland prairies, loess hill prairies, glades, and openings of dry upland
forests; also pastures, railroads, and roadsides.
Specimens from
15 (so far) counties scattered nearly throughout the state are referable to Helianthus
×laetiflorus Pers., which comprises a series of hexaploid (2n=102)
hybrids and backcrosses between H. pauciflorus and H. tuberosus.
Steyermark (1963) and some other earlier authors considered this a true
species, but its hybrid origins have now been confirmed with data from
morphology, artificial crosses, and chemical compounds. It has a relatively
broad distribution in the midwestern states (sometimes forming populations in
the absence of both parents) and also occurs sporadically farther east. The
natural range of the taxon is not known with certainty, as it has been
cultivated as a garden ornamental for a long time and subsequently escaped from
cultivation. Fertility apparently varies a great deal from plant to plant
(Heiser et al., 1969). It differs most notably from H. pauciflorus in
its yellow disc corollas and from H. tuberosus in its more strongly
unequal, relatively short involucral bracts.
Helianthus
pauciflorus was long
known as H. rigidus, but the former is the older of the two available names
(Spring and Schilling, 1990; Kartesz and Gandhi, 1990). Most botanists
currently accept two morphologically overlapping subspecies within H.
pauciflorus.