Houstonia (plant)

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Bluets (Houstonia caerulea) Hedyotis caerulea.jpg
Houstonia caerulea
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Gentianales
Family: Rubiaceae
Subfamily: Rubioideae
Tribe: Spermacoceae
Genus: Houstonia
  • Poiretia J.F.Gmel. non Vent.
  • Panetos Raf.
  • Chamisme Nieuwl.

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.[2] Another five species are classified in the genus Stenaria (Houstonia without Stenaria is paraphyletic).[3] Close relatives of the genus are Oldenlandia microtheca and, more distantly, Arcytophyllum.[4]


Species accepted as of May 2014:[5]

  1. Houstonia acerosa (A.Gray) Benth. & Hook.f. - Chihuahua, Coahuila, Nuevo León, Tamaulipas, San Luis Potosí, Texas, New Mexico
  2. Houstonia caerulea L. - Azure bluet - eastern Canada, eastern United States
  3. Houstonia canadensis Willd. ex Roem. & Schult. - Canadian summer bluet - eastern United States, Ontario, Saskatchewan
  4. Houstonia correllii (W.H.Lewis) Terrell - Correll's bluet - Texas
  5. Houstonia croftiae Britton & Rusby - Croft's bluet - Texas
  6. Houstonia humifusa A.Gray - Matted bluet - Texas, Oklahoma, New Mexico
  7. Houstonia longifolia Gaertn. - Longleaf summer bluet - eastern and central United States; central Canada
  8. Houstonia micrantha (Shinners) Terrell - Southern bluet - central and southeastern United States
  9. Houstonia ouachitana (E.B.Sm.) Terrell - Ouachita bluet - Arkansas, Oklahoma
  10. Houstonia palmeri A.Gray - Coahuila, Nuevo León
  11. Houstonia parviflora Holz. ex Greenm. - Greenman's bluet - Texas
  12. Houstonia procumbens (J.F.Gmel.) Standl. - Roundleaf bluet - Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina
  13. Houstonia purpurea L. - Venus' pride - eastern and central United States
  14. Houstonia pusilla Schöpf - Tiny bluet - central and southeastern United States plus Arizona
  15. Houstonia rosea (Raf.) Terrell - Rose bluet - south-central United States
  16. Houstonia rubra Cav. - Red bluet - northern and Central Mexico as far south as Puebla; southwestern United States (Arizona, New Mexico, Texas, Utah)
  17. Houstonia serpyllifolia Michx. - Creeping Bluet, Mountain Bluet, Thymeleaf Bluet, Appalachian Bluet - Appalachian Mountains from Pennsylvania to Georgia
  18. Houstonia sharpii Terrell - Hidalgo, Veracruz
  19. Houstonia spellenbergii (G.L.Nesom & Vorobik) Terrell - Chihuahua
  20. Houstonia subviscosa A.Gray - Nodding bluet - Texas
  21. Houstonia teretifolia Terrell - Coahuila
  22. Houstonia wrightii A.Gray - Pygmy bluet - Arizona, New Mexico, Texas, Mexico


  1. ^ "World Checklist of Selected Plant Families". 
  2. ^ 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 
  3. ^ Sheri A. Church; 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, PMID 21646157 
  4. ^ 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. 
  5. ^ Kew World Checklist of Selected Plant Families