2. Silphium integrifolium Michx. (rosinweed)
Pl. 289 d; Map
1227
Plants with
short, stout rhizomes. Stems 40–200 cm long, solitary or more commonly
appearing clustered, more or less circular in cross-section (often finely
many-angled), glabrous or moderately to densely pubescent (variously velvety to
roughened) with relatively short (mostly 0.1–0.5 mm), slender to stout hairs,
if glabrous then sometimes strongly glaucous. Leaves usually relatively thick
and sometimes somewhat leathery, the upper surface glabrous or sparsely to
strongly roughened, the undersurface glabrous or moderately to densely
roughened or hairy with short, sometimes pustular-based hairs, when glabrous
both surfaces sometimes moderately to strongly glaucous. Basal and lowermost
stem leaves absent or withered at flowering, with a winged, more or less
petiolar base, the bases slightly expanded and somewhat clasping or wrapped
around the stem, the blade 7–15 cm long, ovate to elliptic-ovate or narrowly
ovate, unlobed, tapered to a usually sharply pointed tip, tapered at the base,
the margins entire or finely to occasionally coarsely toothed and usually with
minute, more or less appressed hairs. Stem leaves somewhat reduced toward the
tip of the stem, opposite (rarely alternate or in whorls of 3), 3–17 cm long,
sessile, lanceolate to ovate, broadly ovate, or somewhat heart-shaped, angled
to tapered or more commonly rounded to shallowly cordate at the base, sometimes
clasping the stem (but not perfoliate), angled or tapered to a sharply pointed
tip. Inflorescences loose, open clusters or panicles, rarely of solitary heads,
the heads long-stalked to short-stalked or nearly sessile. Involucral bracts 25–38,
10–22 mm long, elliptic to ovate, spreading at the sharply pointed tip, the
surfaces glabrous or moderately to densely short-hairy, sometimes also with
stalked and/or sessile glands, the margins glabrous or more commonly with
short, ascending to spreading hairs. Receptacle 1.5–2.5 cm in diameter. Ray
florets (17–)20–35, the corolla 20–50 mm long. Disc florets numerous, the
corolla 4.5–5.5 mm long, slightly shorter than or extending slightly beyond the
tips of the chaffy bracts. Fruits 8–12 mm long, the surfaces glabrous or
inconspicuously but densely hairy, the angles with relatively broad, lighter
wings, each wing rounded to somewhat angled at the tip, the fruit usually with
a narrowly U-shaped apical notch. 2n=14. July–September.
Scattered nearly
throughout the state (Wyoming to New Mexico east to Michigan and Alabama;
Canada). Upland prairies, loess hill prairies, openings of mesic to dry upland
forests, savannas, tops of bluffs, glades, banks of streams and rivers, and
rarely margins of ponds and lakes; also pastures, edges of crop fields,
ditches, railroads, and roadsides.
Apparent hybrids
between S. integrifolium and S. perfoliatum have been collected
in Bates and Warren Counties and are to be expected sporadically at other sites
where the two putative parents grow in proximity.