This globally rare species has a somewhat fragmented range, centered on the southern Appalachians but with disjunct populations in some adjacent regions (Gray 2006; K). In Ky. the only confirmed coll. is from WHIT (KY) by E. Hartowicz, at a site in the Rugged Hills with Cladrastis (T. Littlefield, pers. comm.). Another coll. has been reported by BA from PIKE (by F. Levy for NCU), but the identification appears to have been erroneous. C. verticillata differs sufficiently from other Collinsonia species to be placed in its own subgenus: Mitcheliella (Peirson et al. 2006). It differs as follows (W): inflorescence an unbranched thyrse (versus a panicle or rarely unbranched), the lower nodes with 3-6 flowers per node (versus 2); floral bracts absent (versus minute to large); pedicels flattened at base (versus not basally enlarged); leaves 2-6, usually 4 (versus 6 or more), the upper pairs subverticillate (versus separated), all long-petioled (versus short-petioled to sessile); flowers light pink to lavender (versus cream to yellow). It flowers earlier than canadensis (Apr-Jun versus Jul-Sep) and it can extend into drier woods (W). Typical habitat in se. Ohio is on mesic to subxeric slopes with frequent Quercus alba, Acer saccharum, A. rubrum, Liriodendron tulipifera, Pinus strobus and Viburnum dentatum (sensu lato); the herb layer included Anemonella thalictroides, Galium triflorum, Parthenocissus quinquefolia and Viola sororia (Gray 2006).