Know Your Natives – Hairy Woodland Sunflower

Hairy woodland sunflower (Helianthus hirsutus), of the Sunflower, Aster, or Composite (Asteraceae) family, is one of three Arkansas species with the common name “woodland sunflower.” The genus name is based on Greek words for “sun” and “flower.” The specific epithet is Latin for “hairy” or “bristly.” In the U.S., hairy woodland sunflower occurs from the Florida panhandle west to east-central Texas and north to the Carolinas, Ohio, and Minnesota. The species also occurs in south-central Canada and mountainous areas of central Mexico. In Arkansas, occurrence is statewide. Habitats include woodland edges, savannas, and prairies in loamy to rocky, moist to dry soils. Other common names are bristly sunflower and stiff-haired sunflower.

Hairy woodland sunflower bears near-surface, narrow, ropy, white rhizomes (underground stems). New plants develop at rhizome tips while the established rootstock continues to produce annual stems, so that colonies form quickly.

Photo 1: These spring-time stems are probably clonal. Dense pubescence, becoming bristly and coarse, persists throughout the growth year.
Photo 1: These spring-time stems are probably clonal. Dense pubescence, becoming bristly and coarse, persists throughout the growth year.

This herbaceous perennial produces erect to leaning, rigid stems to 5+ feet tall with opposite, decussate (alternating 90 degrees) leaf pairs. Petiole bases join around the stem as a slight ridge. Stems are densely covered with coarse, bristly hairs. Branching is limited to one to several opposite pairs of short axillary floral branches along the uppermost length of stems. A mature stem may have 10 to 20 pairs of larger leaves below the floral branches, separated by 3 to 4 inch internodes. Overwintering dead stems persist into the new year.

Photo 2: This stem has reached its mature height with the first flowerhead to bloom at the tip of the stem. Several paired axillary floral branches occur along the uppermost length of the stem. Opposite leaf pairs are decussate, emerging at 90 degree angles from one another.
Photo 2: This stem has reached its mature height with the first flowerhead to bloom at the tip of the stem. Several paired axillary floral branches occur along the uppermost length of the stem. Opposite leaf pairs are decussate, emerging at 90 degree angles from one another.

Typical leaves below the floral branches are broadly lanceolate, about 6 inches long (including petioles) and 1¾+ inches wide, with shallowly serrate margins. Like the stems, they are hirsute (coarsely hairy). Petioles, stout and pubescent, decrease in length from stem base (¾ inch) to stem apex (1/16 inch). Leaves have three primary veins: the midrib and a pair of laterals.

 

Photo 3: Display showing upper and lower leaf surfaces along with a lower and upper portion of a stem. Primary lateral veins originate off midrib at leaf blade and petiole junction. Stems and both sides of leaves are hairy.
Photo 3: Display showing upper and lower leaf surfaces along with a lower and upper portion of a stem. Primary lateral veins originate off midrib at or very near the leaf blade and petiole junction. Stems and both sides of leaves are stiff, bristly hairy.

The inflorescence, occurring for a month or more in mid- to late summer, consists of one to a half dozen or more composite flower heads per stem. Flower heads terminate the main stem as well as the stem-like peduncles (½-2 inches long) of lateral branches. 

Photo 4: Within this developing inflorescence, emerging opposite pairs of floral branches bear opposite leaf pairs as well as still smaller leaves that subtend the peduncles.
Photo 4: Within this developing inflorescence, emerging opposite pairs of floral branches bear opposite leaf pairs as well as still smaller leaves that subtend the peduncles.

Flowerheads, 2+ inches across, are set in a bowl-shaped involucre which may be from ½ to 1 inch wide. Flower heads have 10 to 16 sterile ray florets which surround up to 90 or so fertile florets in the central disk. Involucres comprise 20 or so phyllaries (bracts) in three to four imbricated series. The ¼+ inch phyllaries are lanceolate, narrowing to sharp, ascending to revolute tips.

Photo 5: The bowl-shaped involucre has several series of lanceolate phyllaries. Hirsute pubescence is dense on phyllaries, peduncles and leaves. A budded flowerhead is at lower left.
Photo 5: The bowl-shaped involucre has several series of lanceolate phyllaries. Hirsute pubescence is dense on phyllaries, peduncles and leaves. A budded flowerhead is at lower left.

Ray and disk florets are a bright yellow with the ray florets remaining at anthesis as the disk florets bloom in sequence centripetally (from the outermost disk florets into the center of the disk). Ray florets have elongate petal-like corollas (ligules) to ¾ inch long, somewhat ridged longitudinally. Disc florets are each subtended by light yellow, chaffy, receptacular bracts. The 1/4-inch-long tubular disk floret corollas have 5 stubby triangular lobes; the 5 stamens have purplish anthers, fused into a ring. At anthesis, the style emerges through the exserted ring of anthers, carrying with it their yellow pollen, which is now available to pollinators. The stamens then shrink back into the corolla, and the style divides to expose two elongate, recurved stigmatic surfaces.

Photo 6: This 2-inch-diameter flower head has 16 sterile ray florets and numerous fertile disk florets. Each disk florets is subtended by a small, chaffy bract which shields the floret prior to anthesis. Pollen presentation by the immature styles and mature (receptive), recurved stigmas can be seen.
Photo 6: This 2-inch-diameter flower head has 16 sterile ray florets and numerous fertile disk florets. Each disk florets is subtended by a small, chaffy bract which shields the floret prior to anthesis. Pollen presentation by the immature styles and mature (receptive), recurved stigmas can be seen.
Photo 7: Longitudinal section of the flower head shows the somewhat conical receptacle as well as disk florets on their inferior ovaries. Note the shrunken anther ring of the floret at far-right, as the style splits and recurves.
Photo 7: Longitudinal section of the flower head shows the somewhat conical receptacle as well as disk florets on their inferior ovaries. Note the shrunken anther ring of the floret at far-right, as the style splits and recurves.

The perfect disk florets (with stamens and pistils) have, like all composites, inferior ovaries. With fertilization, ovaries harden into dry, narrowly ovoid, 1-seeded fruits (achenes) about ⅛ inch long, with a pair of loosely attached awns at their apex. These are the familiar “sunflower seeds.”

Hairy woodland sunflower is well suited for a larger native plant garden where this tall, leaning plant with its rather aggressive colonizing nature can be accommodated. It is an important  fall and winter food source for wildlife, including butterflies, moths, birds, and small mammals. Long-dead stems can be removed for a more tidy spring garden.

Fifteen additional species and subspecies of sunflowers (Helianthus) occur in Arkansas. Of these, two other woodland sunflowers, H. strumosus and H. divaricatus may become confused with H. hirsutus. All three are widespread in the state, with similar growth habits and habitats. With close examination, H. hirsutus  may be distinguished from the other two species by morphology of the involucre and degree of pubescence (see links immediately above). Another species that may become confused with the woodland sunflowers is Jerusaleum artichoke (H. tuberosus). Hybridization among the three woodland sunflowers makes an already difficult determination even harder.

Photo 8: The “woodland sunflower” species can be distinguished by examining involucres and pubescence. Displayed left to right: H. strumosus, H. divaricatus and H. hirsutus. The “design” of three primary veins of H. divaricatus and H. hirsutus is similar (laterals join midrib at or near the leaf blade base) as compared to H. strumosus (laterals join above base). Flower head size, although not defining, can be helpful.
Photo 8: The “woodland sunflower” species can be distinguished by examining involucres and pubescence. Displayed left to right: H. strumosus, H. divaricatus and H. hirsutus. The “design” of three primary veins of H. divaricatus and H. hirsutus is similar (laterals join midrib at or near the leaf blade base) as compared to H. strumosus (laterals join above base). Flower head size, although not defining, can be helpful.

Article and photographs by ANPS member Sid Vogelpohl

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