Houstonia palmeri A. Gray

Houstonia palmeri A. Gray, Proc. Am. Acad. 17: 202. 1882
Erect perennial, 5-15 cm. high, the stems few, much branched, scaberulo-puberulent or glabra ce, the internodes mostly longer than the leaves; stipules minute, triangular or subtruncate, usually cuspidate, denticulate; leaves sessile, linear or linear-filiform, 5-18 mm. long, obtuse or acute, thick and somewhat rigid, glabrous, the margins revolute; flowers very laxly cymose or axillary, the pedicels stout, 5-20 mm. long, ascending; hypanthium at anthesis less than 1 mm. long, glabrous; calyx-lobes linear or lance-linear, acute or subobtuse, more than twice as long as the hypanthium, ciliolate, in fruit usually much longer than the capsule; corolla salverform, 8-10 mm. long, purplish, glabrous outside, the lobes oblong, obtuse, slightly shorter than the tube, white-villous within; capsule subglobose, 2.5-3 mm. long and about as wide, slightly compressed, half or slightly more than half inferior, rounded or subretuse at the apex, the free portion scabrous; seeds crateriform, about 1 mm. long, roundedoblong, with a conspicuous hilar ridge, coarsely scrobiculate, black.
Type locality: In the mountains east and south of Saltillo, Coahuila. Distribution: Coahuila.

Houstonia palmeri, the Saltillo bluet, is a plant species in the family Rubiaceae, native to the Mexican states of Coahuila and Nuevo León.

Two varieties are recognized:

Houstonia palmeri var. palmeri Houstonia palmeri var. muzquizana (B.L.Turner) Terrell