The Collaborative International Dictionary of English v.0.48:

Houstonia \Hous*to"ni*a\, n. [NL. So named after Dr. William
   Houston, an English surgeon and botanist.] (Bot.)
   A genus of small rubiaceous herbs, having tetramerous
   salveform blue or white flower. There are about twenty
   species, natives of North America. Also, a plant of this
   genus.
   [Webster 1913 Suppl.]

U.S. Gazetteer (1990):

Houstonia, MO (city, FIPS 33256)
  Location: 38.89943 N, 93.35980 W
  Population (1990): 283 (113 housing units)
  Area: 0.5 sq km (land), 0.0 sq km (water)
  Zip code(s): 65333