Helianthus pauciflorus ssp. subrhomboideus

Native

Dry to moderately wet. Prairies, upland forest openings, pastures, railroads, roadsides.

July to September

Yellow ray florets, reddish-brown to purple disk florets

12″ to 48″

This is an erect, 12″ to 48″ tall, annual forb that rises on a single stem from long, thick, branched, creeping rhizomes. It often forms colonies.

The stems are erect, green or reddish-brown, and unbranched or sparingly branched near the top. They are rough to the touch due to a moderate to dense covering of short, stiff, ascending to spreading hairs. The stems are usually leafless near the top.

There are usually 5 to 10 leaf nodes below the inflorescence. Lower leaves are opposite, uppermost leaves are usually also opposite. Lower and middle leaves are rhombic egg-shaped to lance-linear, relatively thick, and flat, not folded longitudinally. They are 2″ to 4¾″ long and ¾″ to 2⅜″ wide, 2½ to 8 times as long as wide. They are wedge-shaped at the base and taper to a blunt or sharp point at the tip with straight sides along the tip. The upper and lower surfaces are rough to the touch due to a moderate to dense covering of minute, stiff hairs. They are also sparsely to moderately covered with minute, stalkless, yellow glands. The margins are finely toothed to almost untoothed. The leaves have 3 main veins, a midvein and a pair of lateral veins that branch off the main vein well above the base and arch upward.

The inflorescence is sometimes a solitary head, usually an open cluster of 2 to 10 flower heads at the end of the stem. The flower heads are on stalks that are 13 ⁄16″ to 4¾″ long.

The whorl of bracts at the base of the flower head (involucre) is ⅝″ to ⅞″ in diameter. The bracts of the involucre are elliptic to egg-shaped and taper to a blunt or sharp point at the tip. The tips of the bracts are tightly appressed.

The flower heads are 1½″ to 2½″ wide, the disk is ⅜″ to 1″ in diameter. There are 10 to 20 yellow ray florets and 75 or more reddish-brown to purple disk florets.

The fruit is an achene.

Stiff sunflower (Helianthus pauciflorus ssp. pauciflorus) tends to be taller, 32″ to 60″ in height. There are usually 5 to 15 leaf nodes below the inflorescence. The uppermost leaves are usually alternate. The lower and middle leaves are longer, 3⅛″ to 10″ long. They are oblong lance-shaped to narrowly egg-shaped and taper to a sharp point at the tip with concave sides along the tip.

Name
The species name pauciflorus means few-flowered.

Allelopathy
The roots exude chemicals that inhibit seed germination and growth of young plants. When in a dense colony, these chemicals may cause the inner plants to die, leaving a ring of living plants.