| Family | Scientific Name | Common Name | Habitat | Distribution | Image |
|---|---|---|---|---|---|
| Rubiaceae | Houstonia nigricans var. 1 | ||||
| Rubiaceae | Houstonia nigricans var. nigricans | Diamond-flower, Glade Bluet, Prairie Bluet | Limestone barrens, limestone glades, limestone rocky bluffs, blackland prairies, longleaf pine sandhills, coastal dunes, coastal grasslands, scrubby pine flatwoods. | Sw. Virginia (Ludwig 1999), s. Michigan, Iowa, Nebraska, and e. Colorado, south to s. Florida, Texas, e. New Mexico, and along the Sierra Madre Oriental to Hidalgo, Mexico. Turner (1995b) reports Houstonia nigricans var. nigricans (as Hedyotis nigricans var. nigricans) from Pickens County, South Carolina; the documentation is not known to me, and suitable habitats there are unlikely. |  (c) Krakowiak, Alaina - CC-BY-NC, permission granted to NCBG |
| Rubiaceae | Houstonia nigricans var. pulvinata | Florida Dune Diamond-flower | Coastal dunes. | Florida peninsula (Flagler and St. Johns counties). |