Houstonia (bluet) is a genus of plants in the Rubiaceae family. Many species were formerly placed (along with other now-segregate genera) in a more inclusive Hedyotis.
Bluets are often small and delicate. For example, H. rosea may attain a height of only one inch. Some species have a single-stem, while others are more "bunchy." Flowers may be blue, purple, lavender, white, or rose, often with shades of one color present in a single population. Flowers have four sepals, a salverform corolla with four lobes, and an inferior ovary. Some species exhibit heterostyly. The fruit is many-seeded capsule which usually dehisces via a suture across the apex; often the capsule is roughly heart-shaped.
Houstonia consists of 20 species native to North America. Another five species are classified in the genus Stenaria (Houstonia without Stenaria is paraphyletic). Close relatives of the genus are Oldenlandia microtheca and, more distantly, Arcytophyllum.
Species accepted as of May 2014:
- Houstonia acerosa (A.Gray) Benth. & Hook.f. - Chihuahua, Coahuila, Nuevo León, Tamaulipas, San Luis Potosí, Texas, New Mexico
- Houstonia caerulea L. - Azure bluet - eastern Canada, eastern United States
- Houstonia canadensis Willd. ex Roem. & Schult. - Canadian summer bluet - eastern United States, Ontario, Saskatchewan
- Houstonia correllii (W.H.Lewis) Terrell - Correll's bluet - Texas
- Houstonia croftiae Britton & Rusby - Croft's bluet - Texas
- Houstonia humifusa A.Gray - Matted bluet - Texas, Oklahoma, New Mexico
- Houstonia longifolia Gaertn. - Longleaf summer bluet - eastern and central United States; central Canada
- Houstonia micrantha (Shinners) Terrell - Southern bluet - central and southeastern United States
- Houstonia ouachitana (E.B.Sm.) Terrell - Ouachita bluet - Arkansas, Oklahoma
- Houstonia palmeri A.Gray - Coahuila, Nuevo León
- Houstonia parviflora Holz. ex Greenm. - Greenman's bluet - Texas
- Houstonia procumbens (J.F.Gmel.) Standl. - Roundleaf bluet - Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina
- Houstonia purpurea L. - Venus' pride - eastern and central United States
- Houstonia pusilla Schöpf - Tiny bluet - central and southeastern United States plus Arizona
- Houstonia rosea (Raf.) Terrell - Rose bluet - south-central United States
- Houstonia rubra Cav. - Red bluet - northern and Central Mexico as far south as Puebla; southwestern United States (Arizona, New Mexico, Texas, Utah)
- Houstonia serpyllifolia Michx. - Creeping Bluet, Mountain Bluet, Thymeleaf Bluet, Appalachian Bluet - Appalachian Mountains from Pennsylvania to Georgia
- Houstonia sharpii Terrell - Hidalgo, Veracruz
- Houstonia spellenbergii (G.L.Nesom & Vorobik) Terrell - Chihuahua
- Houstonia subviscosa A.Gray - Nodding bluet - Texas
- Houstonia teretifolia Terrell - Coahuila
- Houstonia wrightii A.Gray - Pygmy bluet - Arizona, New Mexico, Texas, Mexico
|Wikimedia Commons has media related to Houstonia.|
- "World Checklist of Selected Plant Families".
- Edward E. Terrell (Jun 10, 1996), "Revision of Houstonia (Rubiaceae-Hedyotideae)", Systematic Botany Monographs (American Society of Plant Taxonomists) 48: 1–118, doi:10.2307/25027862, JSTOR 25027862
- Sheri A. Church and Douglas R. Taylor (2005), "Speciation and hybridization among Houstonia (Rubiaceae) species: the influence of polyploidy on reticulate evolution", American Journal of Botany 92 (8): 1372–1380, doi:10.3732/ajb.92.8.1372
- Groeninckx, I., Dessein, S., Ochoterena, H., Persson, C., Motley, T.J., Kårehed, J., Bremer, B., Huysmans, S., Smets, E. (2009). "Phylogeny of the Herbaceous Tribe Spermacoceae (Rubiaceae) Based on Plastid DNA Data". Annals of the Missouri Botanical Garden 96 (1): 109–132. doi:10.3417/2006201.
- Kew World Checklist of Selected Plant Families