Sunflowers

Sunflowers are members of the Aster family (Asteracease), and are classified in the genus Helianthus – from the Greek (“helios” meaning sun and “anthos” meaning flower).

Native sunflowers have smooth to variably hairy stems, hairy leaves and daisy-like yellow to golden yellow petals. I have three sunflowers in my yard. They grow in quite different soils, and they grow to be different heights, ranging  from three- to twelve-feet high.

The native Ox Eye Sunflower and the Sawtooth Sunflower are common to all but one of the southwest states, with the exception of Washington. The native Woodland Sunflower is common the all states east of the Mississippi and the western states along the Mississippi River, except Minnesota.

They are aggressive. The root system is fibrous and rhizomatous and form clonal colonies of variable size.

Woodland Sunflower (Heliantus divaricatus)

The Woodland Sunflower has a composite flower and is 1½ to 4 inches across and consists of eight to fifteen ray florets. The yellow corollas are petal-like and widely spreading to recurved appearance.

At the base of each blossom there are phyllaries or floral bracts, which are arranged in several overlapping series. These are light green and linear-lanceolate in shape, becoming slightly recurved when the flower blooms. They have short stiff hairs or smooth.

The blooming period occurs from mid-summer to early fall for about two months. Later, the corollas are replaced by achenes about 2 mm (1/4 inch) long. They are oval and somewhat flattened seed, but with two bristly scales at the tip.

The Stems and Leaves

The stems are 2½ to 6 feet tall. This stem is light green to dark purple, slender, smooth to sparsely covered with short stiff hairs (sandpapery texture), and sometimes glaucous (covered with a bluish waxy or powdery bloom as a plum is). There is branching on the upper half of the plants where the central and secondary stems terminate in slender peduncles where flowers occur. Flowering stems are rough textured.

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 to 6 inches long and ½ to 2 inches across. They are rather wide, either toothless or with spaced teeth. The base of each leaf blade is rounded-truncate, while its tip is long and gradually tapering. The leaves taper into slender petioles. The upper surface of the leaf blades is yellowish green to medium green and moderately covered with short stiff hairs, with pale lower underneath.

The Woodland Sunflower is normally found in relatively dry upland habitats and normally prefers woody and shady areas.

Ox Eye Sunflower (Heliopsis helianthoides) or False Sunflower

This sunflower is about 1½ to 3 inches across. Each flower consists of 8 to 20 ray florets that surround numerous disk florets. The golden yellow to orange-yellow corolla are triangular in shape and spreading to recurved appearance. Both the ray florets and disk florets of the flowers are fertile.

At the base of flower, there are several outer floral bracts that are arranged in a single series. These phyllaries are light to medium green and oblong-ovate in shape, tapering abruptly to blunt tips that are recurved when the flower blooms. They are rough-hairy.

Blooming periods occur from early summer to late summer, lasting about three months. The florets are replaced by achenes that are 4 to 5 mm (1/2 – 5/8 inch) long. They are oval, somewhat flattened, and dark-colored.

The Stem and Leaves

This sunflower is 3 to 5 feet tall, branching occasionally and becoming bushy. The stems are light green to reddish green and  have downy, short hairs or variably hairs. Pairs of opposite leaves are distributed evenly along these stems. These leaves are 2½ to 5 inches long and 1 to 3½ inches across; they are lanceolate in shape, while their margins are coarsely serrated. The upper leaf surface is medium to dark green and with minute stiff hairs (sandpapery texture), while the lower leaf surface is light green. The leaves taper into slender petioles. There is branching on the upper half of the plant where flowers occur.

The preference is full to partial sun, moist to mesic conditions. Powdery mildew may affect the leaves.

Sawtooth Sunflower (Helianthus grosseserratus)

The upper stems terminate into either individual or small clusters of flowers. Each sunflower is 2½ to 4 inches across, consisting of 10 to 20 ray florets that surround numerous disk florets. The tiny corollas of the disk florets are tubular-shaped and yellow, while the petaloid rays along the circumference are bright yellow and oblong in shape.

Around the base of each sunflower, there are floral bracts or phyllaries that are arranged in several overlapping series. These bracts are light green and linear-lanceolate in shape, becoming slightly recurved when the flower blooms. There are fine hairs around the edges especially near the base of a bract.

On a large plant, it is common for several flowers to be bloom at the same time. The blooming period occurs from late summer to fall, lasting about two months. The disk florets are replaced by achenes about 3 to 4 mm (3/8-1/2 inch) in length. They are oval and somewhat flattened, but with two somewhat bristly scales at the top.

This perennial plant is 3 to 12 feet tall. The stout central stem is smooth, glaucous (covered with a bluish waxy or powdery bloom as a plum is) and reddish or reddish-purple in color. There is very little branching, except for some flowering stems that occur along the upper half of the plant. The leaves are up to 8 inches long and 2½ inches across, lanceolate-oblong and either entirely smooth or strongly serrate along their margins. The upper leaf surface is medium to dark green with minute stiff hairs (sandpapery texture); the lower surface is pale green. The leaves are slightly recurved. The leaves are opposite below, but they become either alternate or opposite along the upper half of the plant. The leaves taper gradually into slender petioles that are about ½ inch in length.

The preference is full to partial sun, moist conditions. Powdery mildew may affect the leaves, but this typically occurs during the fall after the blooming period.

Wildlife

The nectar and pollen of the flowers attract a wide variety of insects. (cellaneous flies, Syrphid flies, bee flies, thick-headed flies, etc), butterflies and skippers, and Chauliognathus pennsylvanicus (Goldenrod Soldier Beetle). Other insects feed on the foliage, bore through the stems, suck plant juices, etc. from sunflowers.

Other moths also feed on these wildflowers and some Some vertebrate animals use sunflowers as a food source. Small mammals occasionally eat the seeds and the gopher also feeds on the rhizomes of sunflowers in relatively dry sandy areas.

The Cottontail Rabbit browses on the foliage of seedlings and lower leaves of mature plants, while the White-Tailed Deer occasionally chomps off the stems and upper leaves of mature plants. Because the Woodland Sunflower and other sunflowers are relatively tall and often form dense colonies, they provide good ground cover for many kinds of wildlife.

For reference, I used the Illinois Wildflower and Minnesota Wildflower.

Definitions of Botanical Terminology