What do we mean when we call a plant a “sunflower”? Often, when a plant is called a sunflower, it refers to the common sunflower, Helianthus annuus, or one of its many cultivated forms. But it is also correct to call any species in genus Helianthus a sunflower, because it is the sunflower genus (Helia = sun; anthus = flower). On this page, we’re calling anything in the genus Helianthus a sunflower.
Most people recognize sunflowers when they see them, with their bright yellow ray florets (tiny individual flowers) and rather flattened center of dark disk florets. The disk florets are fertile, producing achenes (sunflower seeds), while the ray florets are sterile (don’t develop seeds). Sunflowers may be annual or perennial. They are upright plants, herbaceous but rather coarse, often with several branches above the midpoint, with several lengthwise lines or ridges along the stems. Leaf blades are simple, often rough textured.
Sunflowers readily hybridize with each other, which can make identification difficult. Not counting hybrids, there are 16 species of Helianthus recorded for Missouri:
- Narrow-leaved (swamp) sunflower (H. angustifolius). Uncommon in the Bootheel’s lowlands; upland prairies, sand prairies, pastures, ditches, roadsides.
- Common sunflower (H. annuus). Nearly absent from the Ozarks and Bootheel lowlands; scattered elsewhere. This is the species domesticated for edible seeds, sunflower oil, birdseed, and a huge variety of colors and shapes for the garden.
- Thin-leaved (pale) sunflower (H. decapetalus). Uncommon in northeastern Missouri; banks of streams and rivers, bottomland forests, moist upland forests in ravines, bases and ledges of bluffs.
- Woodland sunflower (H. divaricatus). Scattered in the Ozark, Ozark Border, and Mississippi Lowlands, uncommon and sporadic in the Glaciated Plains; glades, openings in dry upland forests, tops of bluffs, rarely banks of streams and rivers; also fencerows and roadsides. Usually has distinctive thick, flat, sessile (stalkless) leaves that usually spread from the stem at about a 90-degree angle, but Ozark specimens may not display this clearly.
- Sawtooth sunflower (H. grosseserratus). Absent from most of the southeastern quarter of the state; scattered elsewhere; a wide variety of habitats.
- Hairy (bristly) sunflower (H. hirsutus). Scattered nearly statewide; moist to dry upland forests, upland prairies, sand prairies, ledges and tops of bluffs; banks of streams, rivers, spring branches; pastures, quarries, ditches, roadsides, and more.
- Maximilian sunflower (H. maximilianii). Scattered nearly statewide; calcareous glades, ledges and tops of bluffs, upland prairies, loess hill prairies, old fields, roadsides, and other open, disturbed areas.
- Small woodland sunflower (H. microcephalus). Uncommon on Crowley’s Ridge in southeastern Missouri, and in nearby portions of the Ozarks; moist upland forests, stream banks, margins of acid seeps, rarely also in old fields.
- Ashy sunflower (H. mollis). Common in the Unglaciated Plains; scattered elsewhere in the state but uncommon or absent from most of the Glaciated Plains of northern Missouri; upland prairies and glades, pastures, old fields, fencerows, margins of ditches, railroads, roadsides.
- Naked-stemmed sunflower (H. occidentalis). Scattered mostly in the Ozark and Ozark Border; upland prairies, glades, openings of dry upland forests; also pastures, old fields, fencerows, and roadsides.
- Stiff (prairie) sunflower (H. pauciflorus). Scattered in the Glaciated and Unglaciated Plains, uncommon in the Ozarks and Mississippi Lowlands; upland prairies, loess hill prairies, glades, openings of dry upland forests; also pastures, railroads, roadsides.
- Prairie (Kansas, plains) sunflower (H. petiolaris). Uncommon, mostly south of the Missouri River; upland prairies, sand prairies, tops of bluffs, quarries, railroads, roadsides, and open, disturbed areas, often in sandy soils.
- Willow-leaved sunflower (H. salicifolius). Scattered in the Unglaciated Plains, north locally to Jackson County; introduced in Scott County; upland prairies and rarely sand prairies and calcareous glades; also roadsides. Has become available through native plant nurseries; plants in cultivation often receive kinder growing conditions than they would in the wild and grow surprisingly prolifically and tall, spreading aggressively by rhizomes and seeds.
- Rosinweed sunflower (H. silphioides). Scattered in the Mississippi Lowlands of the Bootheel and westward along the southern portion of the Ozarks to McDonald County; banks of streams, sand prairies, openings of upland forests; also fallow fields, fencerows, and roadsides. The flowers and foliage of this species superficially resemble those of rosinweeds, hence the name.
- Pale-leaved sunflower (H. strumosus). Scattered nearly statewide; bottomland forests, moist upland forests, banks of streams and rivers, bases and ledges of bluffs, fens, and upland prairies; also railroads and roadsides. Very similar to hairy sunflower (H. hirsutus), especially in the Ozarks.
- Jerusalem artichoke (H. tuberosus). Scattered to common statewide; banks of streams, rivers, and spring branches, bottomland forests, moist upland forests, sloughs, margins of ponds and lakes, moist depressions of upland prairies, pastures, fencerows, roadsides, and similar areas. Note: alternate upper leaves, leaf blades relatively coarsely toothed and longer-tapered at the base, involucral bracts that often are darkened toward the base. Produces fleshy, edible tubers (“sunchokes”).
Broadly speaking, the third largest tribe (subgroup) of the aster family is the Heliantheae (sunflower tribe), which contains genus Helianthus plus about 2,500 other species globally; many of these resemble and are called sunflowers.
Also, although the entire Asteraceae family may also be called the “aster” or “daisy” family, many people call it “the sunflower family.” This is the second largest family of vascular plants in the world, comprising more than 32,000 species globally, including sunflowers, asters, daisies, coneflowers, dandelions, ironweeds, goldenrods, zinnias, marigolds, snakeweeds, yarrows, thistles, cornflowers, lettuces, chicory, wormwood, tarragons, ragweeds, blazing stars, artichokes, knapweeds, beggars ticks, chrysanthemums, and many, many more. The family used to be called the Compositae, because all share the same basic type of composite (multiflowered) flower heads. In a very broad sense, all these could be called “sunflowers.”
Many members of the sunflower family resemble members of genus Helianthus because they, too, have showy yellow ray flowers surrounding the disk. Here are some of the common lookalikes in Missouri. Remember, since they’re all in the sunflower family, you could argue that they’re also “sunflowers.”
- Rosinweeds (genus Silphium) generally resemble sunflowers (genus Helianthus), but are generally more resinous and have larger, broader involucral bracts. Here’s another big difference: The disk (center) of the flowerheads is usually smaller than in true sunflowers. Indeed: the disk florets in rosinweeds are staminate (male) and therefore don’t create seeds, just pollen; but the disk florets in sunflowers, as most of us know, create seeds. In rosinweeds, it’s the petal-like ray florets that are pistillate (female) and turn into seeds, while those in sunflowers produce only pollen. We have 6 species of rosinweeds in Missouri, including cup plant (carpenter’s weed), prairie dock, and compass plant.
- Ox-eye, or sunflower heliopsis (Heliopsis helianthoides) looks so much like a sunflower it’s also called false sunflower. You can distinguish it from the many closely related true sunflowers (genus Helianthus) by its conical central disk and by its ray flowers, which dry out but persist, instead of withering and falling off.
- Black-eyed and brown-eyed Susans (Rudbeckia spp.) are well-known as garden plants. There are 9 species recorded for Missouri.
- Gray-headed coneflower and longhead prairie coneflower (Ratibida spp.) have conelike disks that rise above the drooping ray florets.
- More species that could potentially be confused with “true” sunflowers include sneezeweeds (Helenium spp.), tickseeds (Coreopsis and Bidens spp.), coneflowers (Echinacea spp.), crownbeards (Verbesina spp.), and more.