This has a remarkable range, being locally frequent but largely restricted to base-rich soils of the Interior Low Plateau, Cumberland Plateau and adjacent Coastal Plain in Ala., c. Tenn. and e. Miss. (K). It has been recently discovered by Brock (2020) within mesic woods on rocky calcareous slopes, along Whippoorwill Creek in LOGA and Elk Fork in TODD (APSC). These small populations of up to ca. 50 plants at each locality, on the Pennyrhile Karst Plain, are the northernmost known populations of stamineum; the closest known localities are to the south in Cheatham Co., Tenn. The species differs from others in the sessile-cuneatum group as follows (FNA 26, W): petals spreading to horizontal (versus erect to slightly spreading), with 1-2 spiral twists as in an airplane propellor (versus not spirally twisted); anther dehiscence extrorse, toward the outside of the flower (versus introrse, toward the inside of the flower, or latrorse, toward the side); flowers are usually deep marron to blackish, or rarely yellow.