This is centered in and near the Ozark Region. Both silphioides and atrorubens are diploids (2n = 34), typical of woodland trails, thickets and unkempt rights-of-way in regions with a significant history of burning before settlement. They overlap mostly in Tenn., where there appears to be some intergradation. In Ky. there has been confusion between these two taxa, and some colls. need to be rechecked. Some colls. from CALL (WKY) may be hybrids with occidentalis.