4. Helianthus divaricatus L. (woodland sunflower)
Pl. 282 c, d;
Map 1191
Plants perennial
herbs, with relatively slender, long-creeping, branched rhizomes, usually
occurring in colonies. Stems usually solitary, 50–150 cm long, glabrous below
the inflorescence or the uppermost portion of the stem sparsely to moderately
pubescent with short, stiff, loosely ascending, pustular-based hairs, sometimes
somewhat glaucous. Leaves well developed along the stem (usually with 8–20
nodes), opposite, sessile or with a minute petiole less than 5 mm long. Leaf
blades 4–15 cm long, 1–5 cm wide, relatively thick-textured, lanceolate to
narrowly triangular or triangular-ovate (mostly 3–7 times as long as wide),
flat, not folded longitudinally, rounded to truncate or shallowly cordate at
the base, tapered to a sharply pointed tip, the margins finely toothed to
nearly entire, flat, the upper surface strongly roughened with moderate,
minute, stout, broad-based hairs, the undersurface moderately to densely
pubescent with somewhat softer, more or less spreading hairs but usually
lacking sessile, yellow glands, with 3 main veins, the lateral pair branching
from the midnerve at the base of the blade, arching upward. Inflorescences of
solitary terminal heads or appearing as open clusters or occasionally open
panicles. Involucre 8–12 mm long, 10–15 mm in diameter, about as long as or
slightly longer than the tips of the disc corollas, the bracts in 3 or 4
subequal, overlapping series, lanceolate, tapered to a sharply pointed, loosely
ascending to somewhat spreading or recurved tip, the margins with a fringe of
short, spreading to ascending hairs, the outer surface glabrous or more
commonly sparsely to moderately pubescent with short, stout, ascending, often
pustular-based hairs, usually lacking glands. Receptacle convex to
short-conical, the chaffy bracts 5–8 mm long, narrowly oblong to narrowly
oblong-oblanceolate, with 3 short-tapered, sharply pointed lobes at the tip,
these straw-colored or rarely purplish-tinged, the outer surface minutely hairy
toward the tip. Ray florets 5–15, the corolla 1.5–3.0 cm long, the outer
surface usually with sparse, minute hairs. Disc florets with the corolla
4.0–5.5 mm long, the corollas yellow, the lobes often minutely hairy on the
outer surface. Pappus of 2 scales 2.0–2.5 mm long, these lanceolate to narrowly
triangular, tapered to a sharply pointed, often minutely awnlike tip. Fruits
3–4 mm long, wedge-shaped to narrowly obovate, somewhat flattened and more or
less bluntly 4-angled in cross-section, the surface glabrous or with a few
minute hairs at the tip, uniformly brown or with fine, darker and lighter brown
mottling. 2n=34. July–October.
Scattered in the
Ozark, Ozark Border, and Mississippi Lowlands Divisions, uncommon and sporadic
in the Glaciated Plains (eastern U.S. west to Wisconsin, Oklahoma, and
Louisiana; Canada). Glades, savannas, openings of dry upland forests, tops of
bluffs, and rarely banks of streams and rivers; also fencerows and roadsides.
In its typical
phase, H. divaricatus is easily recognized by its thick, flat, sessile
leaves that usually spread from the stem at about a 90-degree angle. However,
as noted by Heiser et al. (1969), plants in the Ozarks are relatively diverse
morphologically and can be difficult to distinguish from some other perennial
woodland sunflowers. Heiser and his colleagues suggested that because plants
growing in the Ozarks tend to have hairier stems and leaves and more numerous
ray florets and involucral bracts than is typical of the species elsewhere in
the Midwest, plants in the region may have hybridized with H. mollis in
the past. This seems less likely than an interpretation of potential
hybridization with other species of woodland sunflowers of the Ozarks. In
Missouri, the principal difficulties are in distinguishing H. divaricatus
from H. hirsutus and H. strumosus, and occasional specimens
(especially those in which only the top of the plant was collected) are
difficult to separate from H. tuberosus. Heiser et al. noted that in
particular the problems of identification involve tetraploid plants of H.
hirsutus and H. strumosus, which both tend to have slightly larger
disc corollas and fruits. They suggested that these polyploid races may have
arisen following past interspecific hybridization with H. divaricatus,
but this hypothesis still needs to be tested.
The distribution
of H. divaricatus in Missouri shown in the present work is broader than
that in Steyermark’s (1963) map. Oddly, the specimens from western Missouri
added since 1963 do not represent populations newly discovered in the field,
but rather are mostly older specimens that Steyermark (1963) had misdetermined
as H. decapetalus. See the treatment of that species for further
discussion.