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Classification System: APG IV

Superregnum: Eukaryota
Regnum: Plantae
Cladus: Angiosperms
Cladus: Eudicots
Cladus: Core eudicots
Cladus: Asterids
Cladus: Lamiids
Ordo: Gentianales

Familia: Rubiaceae
Subfamilia: Rubioideae
Tribus: Spermacoceae
Genus: Houstonia
Species: H. acerosa – H. caerulea – H. canadensis – H. correllii – H. croftiae – H. humifusa – H. longifolia – H. macvaughii – H. micrantha – H. ouachitana – H. palmeri – H. parviflora – H. procumbens – H. prostrata – H. purpurea – H. pusilla – H. rosea – H. rubra – H. serpyllifolia – H. sharpii – H. spellenbergii – H. subviscosa – H. teretifolia – H. wrightii

Houstonia Gronov. ex. L., Sp. Pl. 1: 105. (1753)

Type species: Houstonia caerulea L., Sp. Pl. 1: 105. (1753)


Poiretia J.F.Gmel., Syst. Nat. ed. 13[bis]: 263 (1791)
Panetos Raf., Ann. Gén. Sci. Phys. 5: 227 (1820)
Chamisme Nieuwl., Amer. Midl. Naturalist 4: 92 (1915)


Linnaeus, C. 1753. Species Plantarum 1: 105.
Govaerts, R. et al. 2020. Houstonia in World Checklist of Selected Plant Families. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the internet. Accessed: 2020 Mar. 10. Reference page.
International Plant Names Index. 2020. Houstonia. Published online. Accessed: Mar. 10 2020. 2020. Houstonia. Missouri Botanical Garden. Published on the internet. Accessed: 2020 Mar. 10.

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]

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


"World Checklist of Selected Plant Families".
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
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
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.
Kew World Checklist of Selected Plant Families

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