Flower:

Flowers are about 2 to 3 inches across, 10 to 20 petals (ray flowers). The petals are bright to golden yellow; the center is a darker yellow. There are several to many flowers branching off at the top of the plant, each at the end of a stalk less than 4 inches long.

The bracts are long, narrow, loose and hairy.

Leaves and stem:

Leaves are up to 7 inches long and 2 inches wide, with little or no stalk. The texture of the upper side is very rough but the underside is more softly hairy. The edges are finely to coarsely toothed. Attachment is mostly alternate, but the lower leaves may be oppositely attached.

The stem is stout, covered in spreading hairs, and green or reddish purple.

Fruit:

The center disk forms a head of dry seed, each about 1/8 inch long and without a tuft of hairs but with 2 bristly scales.

Notes:

Giant Sunflower is most similar to Sawtooth Sunflower (Helianthus grosseserratus), which has a hairless stem that often has a white bloom, whereas Giant Sunflower has a hairy stem and hairier leaves. Jerusalem Artichoke (Helianthus tuberosa) is also a tall sunflower, but has shorter (and usually) wider bracts and rather broader leaves.