Helianthus augustifolus, also known as swamp sunflower, grows to a mature height of 6 feet and has 3- to 6-inch-long, rough foliage. The yellow flowers are 2 to 3 inches in diameter and bloom from late summer to fall.
Downy sunflower plants have fuzzy, gray-green foliage and bloom with 3- to 4-inch wide, light yellow flowers between July and October. The flowers of the Helianthus mollis are very attractive to butterflies.
Slender sunflower is among the late-blooming helianthus varieties. Also known as Helianthus gracilientus, the plant has slender stems and blooms profusely with 2-inch wide, yellow, daisy-like flowers from May to October.