Monographs Details: Carlowrightia haplocarpa B.L.Rob. & Greenm.
Authority: Daniel, Thomas F. 1983. Carloivrightia (Acanthaceae). Fl. Neotrop. Monogr. 34: 1-116. (Published by NYBG Press)
Description:Species Description - Erect to spreading subshrub to 4.5 dm high, arising from a woody caudex to 5 mm in diameter. Older stems quadrate or becoming terete with age, 2-4 mm in diameter, glabrate. Younger stems green frequently tinged with red, bisulcate, smooth to multistriate, 1.0-1.8 mm in diameter, pubescent in 2 vertical, decussate lines in the grooves between the ridges, the pubescence eglandular, consisting of an understory of dense, erect to retrorse, trichomes, 0.2-0.4 mm long (strigose), and an overstory of scattered, erect to flexuose, trichomes, 0.8-1.5 mm long (hirsute-villous), the latter either confined to the ridges or scattered over the entire stem, the nodes often more densely pubescent than the internodes. Leaves ascendent to vertical, subsessile to petiolate; petioles 0.5-2.0 mm long, hirsute-villous; laminas often tinged with red along the margins, cordate, (9-)- 1-27(-36) mm long, 5-25(-30) mm wide, mostly 1-2 times longer than wide, subcordate to cordate at base, acute at apex; margins flat to slightly revolute, hirsute-villous-ciliate; surfaces scattered-hirsute-villous, especially along the veins; several orders of venation prominent. Inflorescence typically consisting of 1 or several spicate axes to 10 cm long, collectively forming a terminal panicle. Inflorescence axes pubescent with a mixture of eglandular and glandular trichomes, the eglandular trichomes dense, retrorse, 0.2-0.3 mm long, the glands scattered, 0.2-0.4 mm long. Reduced dichasia opposite at the nodes along the inflorescence axis, each sessile in the axil of a bract; flowers usually reduced to 1 per dichasium, sessile, subtended by 2 bractlets. Bracts sessile, triangular, 1.5-3.0 mm long, 1.5-2.0 mm wide, pubescent like inflorescence axis. Bractlets triangular, 1.0-1.2 mm long, 0.7-1.0 mm wide, pubescent like inflorescence axis. Calyx 2.5-3.5 mm long, the outer surface pubescent like inflorescence axis, the inner surface glabrous to sparsely pubescent; tube 0.5-1.1 mm long; lobes subulate to linear, 2.0-3.0 mm long, 0.50.8 mm wide at base. Corolla subactinomorphic, lavender-blue with a white eye (lacking papillae) outlined and streaked with purple veins on the upper lip, 9.0-12.0 mm long, pubescent on outer surface with trichomes 0.1-0.4 mm long; tube 2.5-3.0 mm long, 1.5-2.0 mm in diameter; upper lip oblanceolate to spatulate, 6.5-9.0 mm long, 2.0-3.0 mm wide, emarginate at apex; lower lip 6.0-8.5 mm long, the lobes identical in form, reflexed, oblanceolate to elliptic, 5.5-8.0 mm long, 1.5-2.5 mm wide. Stamens 5.5-6.0 mm long; filaments blue, 4.0-5.5 mm long, 0.2 mm wide at base, pubescent, the trichomes retrorse, 0.1-0.2 mm long; anthers golden yellow, thecae 1.3-1.6 mm long. Disc 0.2 mm high. Style 7.5-9.0 mm long, often pubescent near base, glabrous above. Stigma lobes 0.3-0.6 mm long. Capsules 10.5-11.5 mm long, pubescent with eglandular trichomes 0.1-0.3 mm long; stipe 5.0-5.5 mm long; head spherical to partially flattened, 6.0-6.5 mm long (including a terminal beak 0.5-0.9 mm long), 4.8-5.6 mm wide; retinacula 2.0-2.4 mm long. Seeds usually 4 per capsule, flat to subconcavoconvex, obliquely circular to cordate in outline, 4.0-4.8 mm long, 3.5-3.8 mm wide, apex rounded; testa papillose to subtuberculate; margins dentate, the teeth often with retrorse barbs. Flowering. Carlowrightia haplocarpa begins to flower in late July and continues into November.

Discussion:Discussion. Only one population of C. haplocarpa was located during this study, that at the type locality along the railroad tracks near Villar. This rare species is one of the most handsome in the genus with brilliant blue corollas, golden yellow anthers, and somewhat lustrous green leaves (often tinged with red along their margins) which are frequently held erect. The red coloration of the stems and leaves was found to be particularly evident on exposed plants whereas those in the shade showed little, if any, red coloration. Although local in distribution, the population studied showed that the species can form extensive populations of several hundred individuals.

The closest morphological relative of C. haplocarpa is C. ovata of east-central Chihuahua. They differ most notably in the following characters: inflorescence axis pubescence (glandular in C. haplocarpa and eglandular in C. ovata), bractlets (triangular, 1.0-1.2 mm long in C. haplocarpa and linear to subulate, 1.5-2.5 mm long in C. ovata), and capsules (10.5-11.5 mm long, pubescent in C. haplocarpa and 8.0-9.0 mm long, glabrous in C. ovata).

Although C. haplocarpa is not known to occur sympatrically with other species of Carlowrightia, C. glandulosa, C. purpurea, C. texana, C. arizonica, and C. parviflora have been collected in nearby localities. Attempts to hybridize C. haplocarpa with four of these species were mostly unsuccessful and no evidence of hybridization was encountered in the field.

Distribution and Ecology: This species is restricted to an area about 90 by 50 kilometers between Guadalcázar and Rio Verde in southcentral San Luis Potosi. To the east its range is bounded by the Sierra Madre Oriental and to the north and west by the Chihuahuan Desert. It occurs on limestone ledges, slopes in oak woods, and in disturbed habitats at elevations of 1500 to 2000 meters.

Distribution:Mexico North America| San Luis PotosĂ­ Mexico North America|