Houstonia rubra Cav.

Houstonia rubra Cav. Ic. 5: 48. 1799
Hedyotis rubra A. Gray, Mem. Am. Acad. II. 4: 61. 1849. Oldenlandia rubra A. Gray, PI. Wright. 2: 68. 1853. Houstonia saxicola Fastw. Proc. Calif. Acad. II. 6: 291. 1896.
Densely cespitose perennial, 4-7 cm. high, from a long slender taproot, much branched below, the stems stout, scaberulous or glabrous, minutely papillose, densely leafy, the internodes very short; stipules minute, with a few short glanduliferous setae; leaves sessile, the lowest oblanceolate-linear, the upper linear, 5-25 mm. long, about 1 mm. wide, mucronate, thick, minutely scaberulous and papillose or glabrous, the margins more or less revolute; flowers axillary, solitary, short-pedicellate, the pedicels recurved in fruit; hypanthium very short, glabrous, minutely papillose; calyx-lobes linear-subulate, about 2 mm. long, somewhat elongate in fruit; corolla purple, rarely white, salverform, 1.5-3 cm. long, the tube slender, ampliate above, glabrous outside, the 4 lobes lance-oblong, 5-8 mm. long, acute, minutely papillose within; anthers 2 mm. long; capsule depressed-globose, subdidymous, 3-5 mm. broad, two thirds superior, minutely papillose; seeds cymbiform, 1-1.5 mm. long, black, scrobiculate.
Type locality: Ixmiquilpan, Hidalgo.
Distribution: Dry hillsides, southeastern Utah, Arizona, and New Mexico to Puebla.

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.

Houstonia rubra là một loài thực vật có hoa trong họ Thiến thảo. Loài này được Cav. mô tả khoa học đầu tiên năm 1799.