woodland sunflower, Helianthus divaricatus 

thin-leaved sunflower, Helianthus decapetalus

Asteraceae (aster family)

Both of these woodland species share a similar range across the eastern US. The woodland sunflower likes conditions a little shadier and a little drier, while thin-leaved sunflower likes a bit more sun and moisture.  Woodland sunflower will grow three to six feet tall, with flowers one and a half to three inches across.  Thin-leaved sunflower will grow to five feet tall and can have slightly larger flowers (two to three and a half inches across).

(both images above: woodland sunflower; below: thin-leaved sunflower)

The most obvious differences between the two lie in the leaves. Woodland sunflower leaves are blunt at the base, sessile (the leaf base touches the stem of the plant), and are exceptionally long-pointed at the tip.  Thin-leaved sunflower has a slightly long-tipped leaf that narrows dramatically into long, winged petioles.