Who doesn’t love sunflowers? Their bright golden, sun-worshipping blooms are symbols of summer. Each flower head or inflorescence holds hundreds of tiny florets. The outer florets (called rays) have a colorful petal-like appendage while the inner florets (called discs) rarely have a showy appendage. They are also noted for their edible seed which is appreciated by a variety of birds and other wildlife (including baseball players) throughout the summer and fall.
The genus of sunflowers is Helianthus. Since “Helios” means sun and “Anthos” means flower – “Helianthus” literally means flower of the sun, or sunflower. There are over 70 species in the genus Helianthus and the vast majority are native to Central America and North America. Species range greatly in height, habitat, and flower size. Yet almost all are noted for their iconic golden daisy flower.
How to Tell Them Apart
Sometimes it is difficult to distinguish one species from another. Defining characteristics like number, size, and color of ray and disc florets; number and arrangement of the leaf-like bracts (collectively called the involucre) below the rays; and size, shape and serrations of leaves help determine the identity of different species. For example, stiff sunflower has a complex arrangement of overlapping bracts in the involucre (called an imbricate involucre), while Western sunflower has a single, simpler layer of bracts for the involucre.
While annual sunflowers (Helianthus annuus) are the species grown for edible seed and oil production, the majority of Helianthus species are perennials. Many of these species are found growing along roadsides, woodlands, and in prairies. There are more than 30 species native to the central and eastern US. These native species can be wonderful additions to home landscapes. Perennial sunflower species tend to have smaller flower heads and "seed" compared to annual sunflowers, but most perennial species produce many more flower heads due to branching of the flower stalks. Several of these perennial species are quite large, often reaching more than 6 feet tall. There are also several species noted for their ability to spread by rhizomes or seed so that they “colonize” an area quickly.
Garden Worthy Sunflowers
As with any ornamental plant, there are several hybrid perennial sunflowers available. ‘Suncatcher’ is a compact hybrid (4 feet tall) with large golden flower heads (4 inches across) that more closely resemble an annual sunflower. ‘Lemon Queen’ is a popular hybrid with more lemon-yellow flower heads on 4- to 6-foot tall plants.
Other species that are native to the Midwest and parts of Iowa include: Prairie sunflower (H. petiolaris), hairy sunflower (H. hirsutus), small woodland sunflower (H. mcirocephalus), and Nuttall’s sunflower (H. nuttallii). Yet, these species are not included in the table below as they tend to be infrequent or rare across Iowa.
There are other members of the Aster Family (Asteraceae) that can share the sunflower common name. While false sunflower (Heliopsis helianthoides) and Mexican sunflower (Tithonia rotundifolia) are members of the Asteraceae family, they are not members of the sunflower (Helianthus) genus.
Perennial Sunflowers for Iowa
| Common Name | Scientific Name | Height (feet) | Flower head (diameter) | Light | Comments |
|---|---|---|---|---|---|
| Ashy Sunflower | H. mollis | 2-4 | 1-3” golden yellow | Full sun | Stiff, sessile, gray-green leaves; prefers dry soils; rare in Iowa |
| Giant Sunflower | H. giganteus | 5-9 | 3" golden yellow | Full sun | Many ray flowers (10-25); prefers moist soils; edible roots; rare in Iowa |
| Jerusalem Artichoke | H. tuberosus | 6-10 | 2-4“golden yellow | Full sun | Edible tuber/root; spreads freely; prefers moist soils; frequent across Iowa |
| Maximilian Sunflower | H. maximiliani | 3-9 | 3-6” pale yellow | Full sun | Flowers in leaf axils; folded, gray-green leaves; reseeds freely; prefers moist soils; frequent across Iowa |
| Pale Woodland Sunflower | H. strumosus | 1.5-5 | 3" yellow w/yellow centers | Full sun to part shade | Leaves with shallow serrations; petiole 1-4cm long; prefers mesic to dry soils; frequent in open woods across Iowa |
| Sawtooth Sunflower | H. grosseserratus | 5-10 | 3-4” gold w/dark centers | Full sun | Long serrated leaves; winged petioles; smooth stems; prefers moist soils; common across Iowa |
| Stiff Sunflower | H. pauciflorus (H. rigidus) | 3-6 | 3-4" yellow w/dark centers | Full sun | Opposite leaves; imbricate involucre; prefers dry soils; common in Iowa |
| Swamp Sunflower | H. angustifolius* | 5-8 | 2-3” yellow w/dark centers | Full sun to part shade | Prefers moist soils; ‘Low Down’ and ‘First Light’ compact cultivars |
| Ten Petaled Sunflower | H. decapetalus | 3-5 | 2-3" yellow with gold dome in center | Full sun to part shade | 8-12 petals per flower; prefers moist upland soils in the woods and wooded slopes |
| Western Sunflower | H. occidentalis | 2-4 | 2-3” yellow with gold centers | Full sun | Drought tolerant; basal leaves; not aggressive spreader; mesic to dry soils; common in Eastern Iowa, rare elsewhere in Iowa |
| Willowleaf Sunflower | H. salicifolius* | 8-10 | Golden yellow with dark centers | Full sun | Narrow, fine leaves; ‘Autumn Gold’ compact cultivar; aggressive spreader; prefers dry soils |
| Woodland Sunflower | H. divaricatus | 2-6 | 2” yellow with golden centers | Full sun to part shade | Many ray flowers (10-25); spreads by rhizomes; prefers dry woods and open spaces; rare in Iowa |
* not listed as Iowa native in BONAP
References:
Antonio, T. and S. Masi. 2001. Sunflower Family in the Upper Midwest. Chicago Botanic Garden. Chicago, IL.
Eilers, L.J. and D.M. Roosa. 1994. The Vascular Plants of Iowa. University of Iowa Press. Iowa City, IA.
Gleason, H.A. and A. Cronquist. 1991. Manual of Vascular Plants of NE US and Adjacent Canada. 2nd Ed. New York Botanic Garden. Bronx, NY.
Kartesz, J.T., The Biota of North America Program (BONAP). 2015. Taxonomic Data Center. (http://www.bonap.net/tdc). Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). BONAP Helianthus
Digital scans of herbarium specimens from Ada Hayden Herbarium at Iowa State University
Creative Commons images:
Helianthus pauciflorus imbricate involucre - "Helianthus pauciflorus (H. rigidus)" by Matt Lavin is licensed under CC BY-SA 2.0.
Helianthus annuus disc and ray flowers - "Sonnenblume (Helianthus annuus)" by blumenbiene is licensed under CC BY 2.0.