Houstonia rupestris Rafinesque. Cliff Diamond-flower. Phen: May-Oct. Hab: Limestone river bluffs and cliffs. Dist: Largely restricted to limestone cliff-tops along the Kentucky River Palisades, the Cumberland River in KY and TN, and perhaps the Sequatchie Valley in TN.

Origin/Endemic status: Endemic

Taxonomy Comments: Not recently given credence, but this taxon appears to warrant recognition a distinctive taxonomic entity (perhaps better treated at varietal rank). Needing additional study.

Synonymy: < Hedyotis nigricans (Lam.) Fosberg – C, Rogers (1987); < Hedyotis nigricans (Lam.) Fosberg var. nigricans – K1, Tn, Terrell (1986), Terrell (1991), Turner (1995b); < Houstonia angustifolia Michx. – S; < Houstonia nigricans (Lam.) Fernald – F, G; < Stenaria nigricans (Lam.) Terrell var. nigricans – K3, K4, Terrell (2001)

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