Houstonia (plant)


Houstonia 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. Another 5 species are classified in the genus Stenaria; Houstonia without Stenaria is paraphyletic. Close relatives of the genus are Oldenlandia microtheca and, more distantly, Arcytophyllum.
Its members superficially resembles species of the genus Myosotis, but are distinguished from the latter by having only 4 sepals instead of 5.

Species

Species accepted as of May 2014 are:
  1. Houstonia acerosa Benth. & Hook.f.: Chihuahua, Coahuila, Nuevo León, Tamaulipas, and San Luis Potosí and Texas and New Mexico, United States
  2. Houstonia caerulea L. : eastern Canada and eastern United States
  3. Houstonia canadensis Willd. ex Roem. & Schult. : Ontario and Saskatchewan, Canada and eastern United States
  4. Houstonia correllii Terrell : Texas, United States
  5. Houstonia croftiae Britton & Rusby : Texas, United States
  6. Houstonia humifusa A.Gray : New Mexico, Oklahoma, and Texas, United States
  7. Houstonia longifolia Gaertn. : eastern and central United States and central Canada
  8. Houstonia micrantha Terrell : central and southeastern United States
  9. Houstonia ouachitana Terrell : Arkansas and Oklahoma, United States
  10. Houstonia palmeri A.Gray: Coahuila and Nuevo León
  11. Houstonia parviflora Holz. ex Greenm. : Texas, United States
  12. Houstonia procumbens Standl. : Louisiana, Mississippi, Alabama, Georgia, Florida, and South Carolina, United States
  13. Houstonia purpurea L. : eastern and central United States
  14. Houstonia pusilla Schöpf : central and southeastern United States and Arizona, United States
  15. Houstonia rosea Terrell : south-central United States
  16. Houstonia rubra Cav. : northern and central Mexico as far south as Puebla and Arizona, New Mexico, Texas, and Utah, United States
  17. Houstonia serpyllifolia Michx. : Appalachian Mountains from Pennsylvania to Georgia, United States
  18. Houstonia sharpii Terrell: Hidalgo and Veracruz
  19. Houstonia spellenbergii Terrell: Chihuahua
  20. Houstonia subviscosa A.Gray : Texas, United States
  21. Houstonia teretifolia Terrell: Coahuila
  22. Houstonia wrightii A.Gray : Arizona, New Mexico, and Texas, United States and Mexico