Houstonia is a genus of plants in the Rubiaceae

Rubiaceae

The Rubiaceae is a family of flowering plants, variously called the coffee family, madder family, or bedstraw family. The group contains many commonly known plants, including the economically important coffee , quinine , and gambier , and the horticulturally valuable madder , west indian jasmine ,...

 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

Oldenlandia

Oldenlandia is a genus of flowering plants in the family Rubiaceae. It is pantropical in distribution and has about 240 species. The type species for the genus is Oldenlandia corymbosa....

and Hedyotis

Hedyotis

Hedyotis is a genus of flowering plants in the family Rubiaceae. Many species of this genus such as Hedyotis biflora, H. corymbosa and H. diffusa are well known medicinal plants. The hedyotis is native to tropical and subtropical Asia and to islands of the northwest Pacific. It comprises about...

.

Species

• Houstonia acerosa
• Houstonia angustifolia
• Houstonia caerulea
  Houstonia caerulea
  Houstonia caerulea is a perennial ornamental plant in the Rubiaceae family.-Description:...
  
  Azure bluet
• Houstonia calycosa
• Houstonia canadensis Canadian summer bluet
• Houstonia ciliolata
• Houstonia setiscaphia
• Houstonia correllii Correll's bluet
• Houstonia croftiae Croft's bluet
• Houstonia filifolia
• Houstonia floridana
• Houstonia humifusa Matted bluet
• Houstonia lanceolata
• Houstonia longifolia
  Houstonia longifolia
  Houstonia longifolia is a perennial plant in the family Rubiaceae. It can be found throughout most of the Eastern United States and Canada....
  
  Longleaf summer bluet
• Houstonia micrantha Southern bluet
• Houstonia minima
• Houstonia montana
• Houstonia mullerae
• Houstonia nigricans Diamondflowers
• Houstonia ouachitana Ouachita bluet
• Houstonia parviflora Greenman's bluet
• Houstonia patens
• Houstonia polypremoides
• Houstonia procumbens Roundleaf bluet
• Houstonia pulvinata
• Houstonia purpurea
  Houstonia purpurea
  Houstonia purpurea is a species of flowering plant in the coffee family known by the common names Venus' pride, woodland bluet, and purple bluet. It is native to the eastern United States....
  
  Venus' pride
• Houstonia pusilla
  Houstonia pusilla
  Houstonia pusilla is a plant in the family Rubiaceae native to the United States and common in the southeastern and central parts of the country. It is a short plant or less in height with a tiny blue toned, yellow centered four lobed flower with a diameter. The plant has a center rosette form...
  
  Tiny bluet
• Houstonia pygmaea
• Houstonia rigidiuscula
• Houstonia rosea Rose bluet
• Houstonia rotundifolia
• Houstonia rubra Red bluet
• Houstonia salina
• Houstonia serpyllifolia Thymeleaf bluet
• Houstonia subviscosa Nodding bluet
• Houstonia tenuifolia
• Houstonia tenuis
• Houstonia wrightii Pygmy bluet