4. Silphium perfoliatum L. (cup plant, cup rosinweed)
Pl. 289 e–h; Map
1229
Plants with
rhizomes. Stems 100–250 cm long, solitary or more commonly appearing clustered,
square in cross-section (strongly 4-angled), glabrous or rarely sparsely
pubescent with relatively short (mostly 0.2–0.5 mm), slender hairs toward the
base (at a few of the lowermost nodes), occasionally slightly glaucous. Leaves
usually relatively thick but not or only slightly leathery, the upper surface
moderately roughened with small pustules and sometimes also with sparse, minute
hairs, the undersurface moderately to densely roughened-pubescent with a
mixture of short and minute, spreading, mostly pustular-based hairs. Basal and
lowermost stem leaves absent or withered at flowering, long-petiolate, the
petioles often expanded into a pair of basal auricles, these wrapped around the
stem and those of the stem leaves often more or less perfoliate, the blade 10–30
cm long, ovate to triangular-ovate, unlobed, tapered to a usually sharply
pointed tip, tapered to angled at the base, the margins otherwise finely to
coarsely toothed and with minute, more or less appressed hairs. Stem leaves
progressively reduced from about the midpoint of the stem, opposite (the
uppermost leaves rarely alternate), 3–35 cm long, the largest pairs of leaves
with short to long, broadly winged petioles, these expanded toward the base and
strongly perfoliate (fused into a leafy cup around the stem) or rarely not
perfoliate, the median and upper leaves mostly short-petiolate to sessile.
Inflorescences loose, open clusters or panicles, the heads long-stalked to
short-stalked or nearly sessile. Involucral bracts 25–38, 12–27 mm long,
elliptic to ovate, loosely ascending to somewhat spreading at the bluntly to
sharply pointed tip, the outer surface usually glabrous, the margins with
minute, ascending hairs. Receptacle 1.5–2.5 cm in diameter. Ray florets 18–35,
the corolla 15–40 mm long. Disc florets numerous, the corolla 6–7 mm long, usually
extending slightly beyond the tips of the chaffy bracts. Fruits 10–15 mm long,
the surfaces glabrous, the angles with relatively broad, lighter wings (tapered
toward the fruit base), each wing irregularly rounded and minutely hairy at the
tip, the fruit with a broadly rounded apical notch. 2n=14. July–September.
Scattered nearly
throughout the state but uncommon in the Mississippi Lowlands Division (eastern
U.S. west to North Dakota and Oklahoma; Canada; introduced in Europe). Banks of
streams and rivers, bottomland forests, and margins of ponds and lakes; also
edges of crop fields, railroads, and roadsides.
Some botanists
have divided S. perfoliatum into two varieties, but the utility in
maintaining these is not evident. The var. connatum (L.) Cronquist (ssp.
connatum (L.) Cruden), differs from var. perfoliatum in having at
least the upper portion of the stem and the stalks of the heads with spreading
hairs, sometimes longer (1–2 mm) hairs on the leaf undersurface, more of the
leaves sessile, and often fewer (8–13) ray florets. It is said to occur in the
mountains and Piedmont portions of North Carolina, Virginia, and West Virginia.
However, Cruden (1962) reported slightly hairy (intermediate) plants from the
extreme western and eastern portions of the species range and called these f. hornemannii
(Schrad.) Cruden. Additionally, Steyermark (1963) included a rare Missouri
variant from Stone County with only the uppermost leaves perfoliate, which he
called f. petiolatum E.J. Palmer & Steyerm. Patterns of overall
morphological variation within the species appear to be more complex than
earlier authors have understood.