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Published In: Species Plantarum 2: 906. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 8/11/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Native

 

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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.

 


 

 
 
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