Helianthus schweinitzii is a perennial species of the sunflower genus Helianthus Linnaeus, a large genus of the aster family Asteraceae, which is one of the largest and most familiar families of flowering plants. Schweinitz’s sunflower is generally 2 meters in height however, young, stressed, or injured plants can be substantially shorter, for example, mowed plants can flower at less than 0.5 meters. Alternatively, plants in ideal conditions can reach 3 meters in height. Compared to most sunflowers in eastern North America, Schweinitz’s sunflower has relatively small heads measuring 6 to 15 millimeters across with a vibrant yellow color. Other Helianthus species are readily distinguished by larger heads often measuring more that 1.5cm wide. 

Schweinitz’s sunflower’s has a preference for soils known to be poor for agricultural use.  The preferred soil types for Schweinitz’s sunflower tend to contain increased rock fragments. Over the past two centuries, the general conversion of the landscape surrounding the Carolina Piedmont to agricultural uses has avoided the preferred soil of Schweinitz’s Sunflower, aiding the survival of this species. 

Habitat

Helianthus Schweinitzii generally occurs on upland flats and gentle slopes where plants are in full to partial sun. This species prefers soils which are typically shallow and claye with increase quantities of slaty rock fragments from weathered metasedimentary rocks. Helianthus Schweinitzii can be found in a variety of soil types to include Iredell, Enon, Badin, Cecil, Misenheimer, Gaston and Zion.  The main unifying factors in all the soils is location on upland interstream flats or gentle slopes, textures are clayey and thin with substantial rock fragments making them poor for agricultural use. It is believed that this species once occurred in natural forest openings or grasslands. Many of the remaining populations occur along roadsides.

Physical characteristics

Schweinitz’s sunflower is generally 2 meters in height however, young, stressed, or injured plants can be substantially shorter, for example, mowed plants can flower at less than 0.5 meters. Alternatively, plants in ideal conditions can reach 3 meters in height. Compared to most sunflowers in eastern North America, Schweinitz’s sunflower has relatively small heads measuring 6 to 15 millimeters across with a vibrant yellow color. The stem is usually unbranched in its lower portion and purple in color, the terminal one-third of the stem is freely branched with branches departing form the stem at about a 45 degree angle. The leaves are arranged in pairs on the lower part of the stem but usually occur singly (or alternate) on the upper parts. Leaves are attached to the stem at right angles, and the tips of the leaves tend to droop. The leaves are thick and stiff, with a rough upper surface. The upper leaf surfaces have broad spiny hairs that are directed toward the tip and soft white hairs cover the underside. The plant produces small yellow flowers from late August until frost.

Lifestyle

While limited information is currently available on the life history or species biology of Schweinitz’s sunflower, it is a long-lived perennial with individuals living for decades.  This species blooms from late August to front.

Reproduction

The species blooms from late August to frost. The relative importance of sexual (by seed) and asexual (by rhizome) reproduction is not known in this species. However, it is able to colonize through the dispersal of seeds that readily germinate without a dormant period.

Mowing at certain seasons can limit seed production and thus the potential reproduction and recovery of the species. For instance, in 1991 nearly all South Carolina populations were mowed in August or September. severely limiting seed production because the mowed plants did not flower or fruit.

Geography

Schweinitz’s sunflower is found in the central Piedmont region of North and South Carolina