Houstonia nigricans (Lamarck) Fernald var. nigricans . Diamond-flower, Glade Bluet, Prairie Bluet. Phen: May-Oct. Hab: Limestone barrens, limestone glades, limestone rocky bluffs, blackland prairies, longleaf pine sandhills, coastal dunes, coastal grasslands, scrubby pine flatwoods. Dist: Sw. VA (Ludwig 1999), s. MI, IA, NE, and e. CO, south to s. FL, TX, e. NM, and along the Sierra Madre Oriental to Hidalgo, Mexico. Turner (1995b) reports Houstonia nigricans var. nigricans (as Hedyotis nigricans var. nigricans) from Pickens County, SC; the documentation is not known to me, and suitable habitats there are unlikely.

Origin/Endemic status: Native

Taxonomy Comments: This species has been variously placed in Houstonia, Hedyotis, and Stenaria. As interpreted by Terrell (1991, 2001) and Turner (1995b), Houstonia nigricans is a polymorphic species, with Houstonia nigricans var. nigricans as a widespread "matrix variety", and other, much more local varieties warranting recognition.

Synonymy: = Ar, Va, Terrell (1986); = Houstonia angustifolia Michx. – S; = n/a – RAB; < Hedyotis nigricans (Lam.) Fosberg – C, GrPl, Il, NcTx, Rogers (1987); > Hedyotis nigricans (Lam.) Fosberg var. filifolia (Chapm.) Shinners – Tx, misapplied; < Hedyotis nigricans (Lam.) Fosberg var. nigricans – K1, Tn, Terrell (1991), Turner (1995b); < Houstonia nigricans (Lam.) Fernald – F, G; < Stenaria nigricans (Lam.) Terrell – Mi; < Stenaria nigricans (Lam.) Terrell var. nigricans – Fl5, K3, WH3, Terrell (2001)

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Heliophily: 9