| Family | Scientific Name | Common Name | Habitat | Distribution | Image |
|---|---|---|---|---|---|
| Rubiaceae | Houstonia caerulea | Quaker Ladies, Innocence, Common Bluet, Pissabed | Forests, woodlands, openings, lawns, a wide variety of disturbed sites. | ME, ON, and WI south to s. GA, s. AL, w. LA, and OK. |  |
| Rubiaceae | Houstonia canadensis | Canada Bluet | Dry limestone barrens (sometimes locally abundant in shallow soils over limestone), limestone woodlands and outcrops. | ME and s. ON west to MI and n. IL, south to sw. VA, se. and c. TN, nw. GA, w. TN, and se. MO (J. Thomas, pers. comm., 2016). |  |
| Rubiaceae | Houstonia croftiae | Croft's Bluet | Sandy open areas, sparsely vegetated areas in grasslands or among shrubs. | Endemic to s. TX (Duval, Hidalgo, Jim Wells, Refugio, San Patricio, Starr, Webb, and Zapata counties). | |
| Rubiaceae | Houstonia floridana | Rockland Bluet | Pine rocklands, marl prairies. | S. FL (Miami-Dade and Monroe counties); n. Bahamas. |  |
| Rubiaceae | Houstonia humifusa | Mat Bluets | Sandy prairies, dunes, other sandy places, disturbed areas. | OK and NM south through se., s. and w. TX. | |
| Rubiaceae | Houstonia lanceolata | Midwestern Summer Bluet, Lanceleaf Bluet, Glade Mountain Houstonia | Calcareous prairies and barrens, dry woodlands, banks, rock outcrops, shallow soils around mafic and calcareous rock outcrops. | H. lanceolata ranges from s. ME and w. NY west to s. OH, and sw. MO, south to w. NC, n. GA, AL, MS, AR, and e. OK. The distribution and ecology of H. lanceolata in our area are poorly known; it apparently occupies drier and typically more circumneutral sites than H. purpurea. |  |
| Rubiaceae | Houstonia longifolia var. compacta | Eastern Longleaf Bluet | Dry rock outcrops and adjacent open woodlands, longleaf pine sandhills, dry sandy woodlands, dry roadbanks, glades and barrens. | Var. compacta is centered in the central Appalachians of VA, WV, e. KY, and se. OH, with extensions north to VT, west into n. IL, and south in the Piedmont and adjacent Coastal Plain to SC, GA, and Panhandle FL. |  |
| Rubiaceae | Houstonia longifolia var. glabra | Granite Dome Bluet | Seasonally and periodically wet soils of shallow soil mats and crevices of granitic domes. | Var. glabra is endemic to the granitic dome district centered around Highlands, NC, occurring in sw. NC, nw. SC, and ne. GA |  |
| Rubiaceae | Houstonia longifolia var. longifolia | Northern Longleaf Bluet | Dry sandy or rocky habitats. | New England and maritime Canada west to MN and SK, south to n. NJ, PA, n. IN, n. IL. |  |
| Rubiaceae | Houstonia micrantha | Southern Bluet | Dunes, sandy soils, granitic flatrocks, other glades, disturbed areas, roadsides. | E. and c. GA west to sc. KY, sw. TN, s. MO, nw. AR, south to w. FL Panhandle, s. MS, s. LA, and e. TX. In 2017-2018, found eastwards of its known native distribution on roadsides and other disturbed areas in Wake County, NC (B. England, pers. comm., 2017, 2018). Reported for Barren County, KY (Brock 2020). |  |
| Rubiaceae | Houstonia montana | Roan Mountain Bluet | In crevices of rock outcrops at the summits of high elevation peaks of the Southern Blue Ridge, also in thin, frost-heaved, gravelly soils of grassy balds near summit outcrops, from 1250-1950 m in elevation. | This species is endemic to the high Blue Ridge of nw. NC, ne. TN, and sw. VA, most notably occurring on Roan Mountain, Grandfather Mountain, Bluff Mountain, and Three Top Mountain. This species was recently found in sw. VA, at Grayson Highlands State Park, Grayson County (G.P. Fleming & K.D. Patterson, pers. comm., 2013). |  |
| 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. 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. |  |
| Rubiaceae | Houstonia nigricans var. pulvinata | Florida Dune Diamond-flower | Coastal dunes. | FL peninsula (Flagler and St. Johns counties). | |
| Rubiaceae | Houstonia ouachitana | Ouachita Bluet, Ouachita Houstonia | Oak forests, bottomlands, openings, generally in more mesic places than H. tenuifolia. | Ouachita Mountains of sw. AR and se. OK. | |
| Rubiaceae | Houstonia parviflora | Greenman's Bluet | Tallgrass prairies. | S. TX; disjunct to nw. AR. | |
| Rubiaceae | Houstonia procumbens | Creeping Bluet, Fairy-footprints, Roundleaf Bluet, Innocence | Beach dunes, moist to wet sandy pinelands and savannas, sandy firelanes. | Se. NC south to s. FL, west to se. LA. |  |
| Rubiaceae | Houstonia purpurea | Summer Bluet, Mountain Bluet | Moist and dry woodlands and forests, thinner soils around rock outcrops, and in a variety of disturbed sites, such as paths, old roads, and roadbanks. | DE, MD, and s. PA west to s. OH, s. IL, and sw. MO south to SC, sw. GA, Panhandle FL, MS, s. LA, e. TX, and e. OK. |  |
| Rubiaceae | Houstonia pusilla | Tiny Bluet | Woodlands, prairies, glades, barrens, lawns, cemeteries, and other disturbed sites. | MD south to Panhandle FL, west to TX, and inland from IL west to NE, south to TN and TX. The natural habitats and original distribution of this species are obscure. |  |
| Rubiaceae | Houstonia rosea | Rose Bluet | Bottomlands, lawns, disturbed areas. | AL west to se. MO, OK, and TX. |  |
| Rubiaceae | Houstonia rupestris | Cliff Diamond-flower | Limestone river bluffs and cliffs. | 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. |  |
| Rubiaceae | Houstonia serpyllifolia | Appalachian Bluet, Thyme-leaf Bluet | Streambanks, grassy balds, moist forests, seepy rock outcrops, spray cliffs, and moist disturbed areas. | A Southern and Central Appalachian endemic: PA south to nw. SC and ne. GA. |  |
| Rubiaceae | Houstonia subviscosa | Nodding Bluet | Sandy soils, dunes. | Nc. TX south through se. and s. TX to (?) ne. Mexico. | |
| Rubiaceae | Houstonia tenuifolia | Diffuse-branched Bluet | Usually in dry woodlands, often rocky (especially mafic rocks) or sandy. | This species is centered in the Southern Appalachians and the Ozarks, extending into provinces adjacent to both areas of concentration, ranging overall from PA west to MO and OK, south to SC, GA, and TX; disjunct in Panhandle FL. |  |
Cite as...