Helianthus grosseserratus

Native

Dry. Prairies, bluff tops, railroads, roadsides, and open, disturbed areas. Full sun. Sandy soil.

June to September

Yellow ray florets, reddish-brown to purple disk florets

24″ to 120″

This is an erect perennial forb that rises on a single stem from a short creeping rhizome or sometimes a longer, thick, branched rhizome. It often forms dense colonies. It can be up to 120″ tall when appearing as a single plant, 24″ to 60″ tall when in a colony.

The stems are erect, stout, round, and green, becoming purple in strong sun. They are sometimes covered with a whitish, waxy bloom (glaucous). They are hairless and usually unbranched below the inflorescence. Within the inflorescence the stems are sparsely to moderately covered with short, appressed, upward pointing hairs.

There are usually 20 to 25 stem leaves. There are no basal leaves. Lower and middle stem leaves are usually alternate, sometimes opposite. Those near the top are always alternate. Lower stem leaves are narrowly lance-shaped to narrowly egg-shaped, 4″ to 12½″ long and 1½″ to 3½″ wide, 5 to 10 times as long as wide. They are often folded along the midrib, especially during hot and dry weather. They are on ¾″ to 2″ long leaf stalks. They are wedge-shaped at the base and taper to a sharp point at the tip. The upper surface is dark green and smooth or slightly rough and sparsely to moderately covered with minute hairs. The lower surface is densely covered with minute, soft, appressed hairs. The margins are coarsely or shallowly toothed. The leaves have a prominent midvein, and a pair of lateral veins that branch off the main vein well above the base and arch upward. The first pair of lateral veins is only slightly more prominent than subsequent pairs.

The inflorescence is occasionally a solitary head, usually an open, branched cluster of 3 to 15 or more flower heads at the end of the stem.

The flower heads are 2½″ to 4″ wide with disk up to ⅝″ wide. They are on stout stalks that are up to 4″ long. There is a whorl of 25 to 30 bracts (involucre) in 2 or 3 overlapping series at the base of the flower head. The involucre is broadly hemispheric in shape and ⅝″ to 1″ in diameter. The bracts are loosely spreading or sometimes ascending, and are spreading or bent backward at the tip. They are narrowly lance-shaped to nearly linear, and taper to a sharply-pointed tip. They are hairless or hairy toward the base, and have a fringe of hairs along the margin, at least near the base.

There are 14 to 20 yellow ray florets and 100 or more yellow disk florets.

The fruit is an achene.

See the Sunflowers ID Filter for a spreadsheet to aid identification of this and similar species.

Rydberg’s sunflower (Helianthus nuttallii ssp. rydbergii) leaves are on shorter stalks, 3 ⁄16″ to ⅝″ long. The leaf blades are smaller, 1½″ to 8″ long and 5 ⁄16″ to 1½″ wide. The margins are untoothed or sparingly toothed. The inflorescence has fewer flower heads, no more than 6. The involucre has 30 to 38 bracts. The flower head has fewer disk florets, 60 or more. In Minnesota it is rare, currently verified in only one location.