Houstonia rubra, the red bluet, is a plant species in the Rubiaceae. It is a small herb with red to reddish-purple flowers, native to the southwestern United States and northern and central Mexico: Coahuila, Nuevo León, Hidalgo, Zacatecas, Guanajuato, Puebla, Sonora, Durango, Chihuahua, Arizona, New Mexico, southeastern Utah and western Texas. References rubra Flora of Arizona Flora of Chihuahua (state) Flora of Coahuila Flora of Durango Flora of Guanajuato Flora of Hidalgo (state) Flora of New Mexico Flora of Nuevo León Flora of Puebla Flora of Texas Flora of Utah Flora of Zacatecas Plants described in 1799 Flora without expected TNC conservation status Taxa named by Antonio José Cavanilles