Rough Sunflower (Priority species: Smokies Discovery Impact Day)

Rough Sunflower

Helianthus divaricatus

Description ⁶

This perennial wildflower is 2½-6' tall with a central stem that becomes branched where the flowerheads occur. This stem is light green to dark purple, slender, terete (round in cross-section), glabrous to sparsely covered with short stiff hairs, and sometimes glaucous. Upper secondary stems have similar characteristics. Pairs of widely spreading opposite leaves occur along the central stem and any secondary stems; each pair of leaves rotates 90° from the pair of leaves below. Leaf blades are 2-6" long and ½-2" across; they are lanceolate-oblong to ovate-oblong in shape, and either toothless or with widely spaced teeth along their short-ciliate margins. The base of each leaf blade is rounded-truncate, while its tip is long and gradually tapering. The upper surface of the leaf blades is yellowish green to medium green and sparsely to moderately covered with short stiff hairs, while the pale lower surface is short-pubescent, especially along the major veins. Three prominent veins join together at the base of each leaf blade. The leaves are sessile or they have short ascending petioles (about 1/8" long). The central and secondary stems terminate in flowerheads on slender peduncles. Individual flowerheads are 1½-3" across, consisting of 8-15 ray florets that surround numerous disk florets. The yellow corollas of the ray florets are petal-like and widely spreading.. The yellow corollas of the disk florets are narrowly tubular (1/8" long or less) with 5 spreading lobes. At the base of each flowerhead, there are light green phyllaries (floral bracts) that are arranged in several overlapping series. Individual phyllaries are linear-lanceolate and ciliate along their margins; the outer phyllaries are widely spreading or recurved when the flowerheads bloom. The peduncles of the flowerheads resemble the stems, except they are more likely to have short stiff hairs. The blooming period occurs from mid-summer to early fall for about 2 months. Afterwards, the disk florets are replaced by achenes about 2 mm. long; these achenes are ovoid-oblongoid and somewhat flattened. At the apex of each achene, there is a pair of tiny chaffy scales that easily become detached. The root system is long-rhizomatous. Vegetative colonies of plants are often formed by the rhizomes.

Habitat ⁷

Habitat is dry thickets and open woods. (Hultman, 1978) Native habitat comprises woodland, savannah, and rocky bluff. (NPIN, 2009) This plant inhabits dry woods and open places. (UW, 2009)

Comments ⁸

The Woodland Sunflower is easily identified by its sessile, or nearly sessile, opposite leaves. Other sunflowers (Helianthus spp.) have longer petioles. Its stems are usually hairless or mostly hairless, unlike Helianthus hirsutus (Hairy Sunflower) and some other species in this genus. Compared to some narrow-leaved sunflowers that occur in prairies, the leaf bases of Woodland Sunflower are more broad and nearly truncate. Some parasitic plants that occasionally attach their haustoria (root-like extensions) to sunflowers and other species in the Aster family include Cuscuta glomerata (Rope Dodder) and other Cuscuta spp. (generally in moist areas that are often sandy), and Orobanche ludoviciana (Prairie Broomrape) and other Orobanche spp. (generally in dry areas that are often sandy). These parasitic plants can significantly weaken the host plants to which they become attached.

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Rough Sunflower

Description 6

Habitat 7

Comments 8