Twenty-five sunflowers and many subspecies are listed in Gray's Manual of Botany, 1950 edition, and of these many are found in Illinois; most of them bloom in September.
Helianthus mollis Lam.
Late Summer Roadsides.
Hairy sunflower (Helianthus mollis) is compact, seldom more than two to three feet tall, has pairs of small, thick, hairy, heart-shaped leaves clasping the hairy or downy stem. Usually one showy sunflower with brown center stands regally at the top of the stalk. A neat, ornamental plant, it is found along sandy prairie roadsides and at the edges of woods. Woodland sunflower (Helianthus divaricatus) grows in dry woods and blooms in July, earlier than the majority of sunflowers, and some-times is the first of its kind to come into bloom. The three to six foot stem is slender, stiff, and fine-hairy, with pairs of opposite leaves ar-ranged rather far apart upon it. One to three flowers are borne on short stalks above the last pair of leaves and are three inches broad with golden-brown center.
Giant sunflower (Helianthus grosseserratus) is truly the giant of them all. The plants often reach a height of eight to twelve feet and are much branched above with abundant flower stems. The leaves are large, jaggedly toothed, in drooping pairs on the rough stem. The upper part of the stem with its numerous branches bears great clusters of bright yellow sunflowers with golden-brown centers. The flowers possess that compelling beauty of the sunflower, and are fragrant with a rich odor reminiscent of chocolate. The giant sunflower is a common border plant along country roads, bottomland roads, and ditches in August and Sep-tember. This is the climax of the year's color: this is the Time of Yellow Flowers.