Helianthus tuberosus, Jerusalem Artichoke
Leaves 3-nerved with coarse teeth and long, winged, petioles; up to 6" wide; lower opposite, middle and upper alternate. Stem rough or hairy, 3 - 9' tall; Adventive.

Helianthus decapetalus, Thinleaf Sunflower
Stem and leaves smooth or slightly hairy; leaves opposite, upper sometimes alternate; leaf stalks only partly winged. 2 - 4' tall. Piedmont only; uncommon.

Helianthus divaricatus, Woodland Sunflower
Leaves "opposite, sessile or short-petioled" and "rough to the touch, like sandpaper." 2 - 6' tall. Rare.

Helianthus giganteus, Tall Sunflower
Leaves pinnately veined and narrow, about an inch wide; stem rough or hairy. 3 - 9' tall. Uncommon.

Helianthus angustifolius, Swamp Sunflower
"Disk corollas with red purplish-brown lobes"; leaves "narrow-lanceolate to linear." 2 - 6' tall. Coastal plain only.

Helianthus annuus, Domesticated Sunflower
This is the common, cultivated species, with striped or black seeds and large flowers (though not so large as in some cultivated plants) with dark central disks. Leaves mostly alternate. 3 - 10' tall. Alien.

Helianthus grosseserratus, Sawtooth Sunflower
Leaves pinnately veined; stem smooth. Up to 6 -15' tall. Adventive.

This species is no longer found in Delaware. Helianthus strumosus, Pale-leaf Sunflower

Sources: The Flora of Delaware, Herbaceous Plants of Maryland, William A. McAvoy.