Houstonia (plant)

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Bluets (Houstonia caerulea) Hedyotis caerulea.jpg
Houstonia caerulea
Scientific classification

  • Poiretia J.F.Gmel. non Vent.
  • Panetos Raf.
  • Chamisme Nieuwl.

Houstonia (bluet) is a genus of plants in the family Rubiaceae. Many species were formerly classified, along with other genera since segregated elsewhere, in a more inclusive genus Hedyotis.

Bluets are often small and delicate. For example, H. rosea may grow only one inch tall. Some species are single stemmed and others have multiple stems in bunches. Flowers are blue, purple, lavender, white, or rose, often with shades of one color present in an individual population. Flowers have 4 sepals, colloquially denominated "petals", a salverform corolla with 4 lobes, and an inferior ovary. Some species exhibit heterostyly. The fruit is an often roughly cordate capsule enclosing many seeds and which usually dehisces via a suture across its apex.

Houstonia consists of 20 species native to North America.[2] Another 5 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]

Its members superficially resembles species of the genus Myosotis (Forget-me-nots), but are distinguished from the latter by having only 4 sepals (petals) instead of 5.


Species accepted as of May 2014 are:[5]

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


  1. ^ "World Checklist of Selected Plant Families".
  2. ^ Edward E. Terrell (10 June 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): 1372–80, 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): 109–32. doi:10.3417/2006201. S2CID 56042261.
  5. ^ Kew World Checklist of Selected Plant Families