Helianthus microcephalus Torr. & A. Gray

Small Woodland Sunflower


CC = 8
CW = 5
MOC = 6

© DETenaglia

Family - Asteraceae/Heliantheae

Habit - Perennial forb with short, thick rhizomes, or lacking rhizomes, sometimes occurring in clumps.

Stems - Ascending to erect, sometimes arching, few to several, to 2.5 m, smooth and glabrous below the inflorescence, often somewhat glaucous.

Helianthus_microcephalus_stem.jpg Stem and nodes. Stems are smooth and often glaucous.

© SRTurner

Leaves - Well developed along the stem, usually with 8-20 nodes, gradually reduced toward the stem tip, mostly opposite, sometimes becoming alternate upward, mostly petiolate, the petioles less than 4 cm long. Blades 4-18 cm long, 1-6 cm wide, relatively thick-textured, lanceolate to narrowly ovate (mostly 4-9 times as long as wide), flat, not folded longitudinally, rounded to short-tapered 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 short, softer, loosely appressed hairs and also with sparse to moderate, sessile, yellow glands, with 3 main veins, the lateral pair branching from the midnerve well above the base of the blade, arching upward.

Helianthus_microcephalus_leaves1.jpg Leaves. Arrangement is typically opposite, but upper nodes are sometimes alternate.

© SRTurner

Helianthus_microcephalus_leaf1.jpg Leaf adaxial.

© SRTurner

Helianthus_microcephalus_leaf1a.jpg Adaxial leaf surface.

© SRTurner

Helianthus_microcephalus_leaf2.jpg Leaf abaxial.

© SRTurner

Helianthus_microcephalus_leaf2a.jpg Abaxial leaf surface.

© SRTurner

Helianthus_microcephalus_leaves.jpg Pressed leaves.

© DETenaglia

Inflorescences - Open clusters or panicles with few to several flowering heads.

Helianthus_microcephalus_inflorescence.jpg Inflorescence.

© SRTurner

Heads - Involucre 5-7 mm long, 8-10 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, narrowly lanceolate, tapered to a sharply pointed, loosely ascending to spreading or recurved tip, the margins with a fringe of short, spreading to ascending hairs, the outer surface glabrous or sparsely hairy toward the base but usually lacking glands. Receptacle convex to short-conical, the chaffy bracts 5-7 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.

Helianthus_microcephalus_heads1.jpg Flowering heads. These are usually not broader than 3 cm, and have a relatively small disk as well.

© SRTurner

Helianthus_microcephalus_heads2.jpg Flowering heads.

© SRTurner

Helianthus_microcephalus_involucre.jpg Involucre.

© SRTurner

Flowers - Ray florets 5-8, the corolla 1.0-1.5 cm long, the outer surface usually with sparse, sessile, yellow glands. Disc florets with the corolla 4.0-5.5 mm long, the corollas yellow, the lobes minutely hairy on the outer surface. Pappus of 2 scales 1.5-2.5 mm long, these lanceolate to narrowly triangular, tapered to a sharply pointed, often minutely awnlike tip.

Helianthus_microcephalus_florets.jpg Disk and ray florets. As in all sunflowers, the ray florets are sterile.

© SRTurner

Fruits - Achenes 3.5-4.5 mm long, wedge-shaped to narrowly obovate, only slightly flattened but more or less bluntly 4-angled in cross-section, the surface glabrous, with fine, darker and lighter brown mottling.

Flowering - August - September.

Habitat - Moist or dry open woods, swampy ground along streams, thickets, sandy fields, typically in acid or clay soils.

Origin - Native to the U.S.

Lookalikes - Other species of Helianthus, particularly H. hirsutus, H. strumosus, and H. tuberosus.

Other info. - This species has the smallest flowering heads of any of Missouri's sunflowers, rarely exceeding 3 cm in diameter. This trait, along with the relatively small number (5-8) of disk florets, serve to distinguish this species from its lookalikes. The plant is uncommon in Missouri, found in just a few counties in the southeastern corner of the state. Beyond Missouri it occurs in several Midwestern and Deep South states.

The epithet microcephalus means "small head."

Photographs taken in Brown Summit, NC., 10-3-02 (DETenaglia); also at Holly Ridge Conservation Area, Stoddard County, MO, 8-16-2021 (SRTurner).