Carlowrightia mexicana Henrickson & T.F.Daniel

  • Authority

    Daniel, Thomas F. 1983. Carloivrightia (Acanthaceae). Fl. Neotrop. Monogr. 34: 1-116. (Published by NYBG Press)

  • Family

    Acanthaceae

  • Scientific Name

    Carlowrightia mexicana Henrickson & T.F.Daniel

  • Type

    Type. Mexico. Coahuila: ca. 30 (air) mi WNW of Cuatro Ciénegas in Cañón Los Pozos, ca. 3-4 mi W of Rancho Cerro de la Madera along trail to Cañón Desiderio (ca. Lat. 27° 08' N, Long. 102° 28' W), elev. 1400 m, 2 May 1977, Henrickson & Lee 16013 (TEX!, holotype; MICH!, isotype).

  • Description

    Species Description - Prostrate to erect, suffrutescent perennial to 3.5 dm high, arising from a woody caudex to 15 mm in diameter or a woody rhizome to 3 mm in diameter. Older stems quadrate to terete or with irregularly fissured bark, 1.5-3.0 mm in diameter, pubescent or glabrate. Younger stems green, quadrate to terete, smooth to multistriate, 0.5-0.8 mm in diameter, pubescent, the trichomes eglandular, retrorse (rarely closely appressed), 0.1-0.2(-0.5) mm long (strigillose), more or less evenly disposed or concentrated in 2 vertical, often decussate lines, the nodes often more densely pubescent with straight trichomes 0.1-0.5 mm long. Leaves ascendent, subsessile to distinctly petiolate; petioles 1-3(-6) mm long, pubescent like the younger stems; laminas elliptic-lanceolate to obovate, commonly more obovate below and becoming more narrowly elliptic-lanceolate above, (4-)8-19(-29) mm long, 0.5-7.0(-9.0) mm wide (infrequently reduced in size acropetally into flower-bearing bracts), mostly (1.5-)2.5-8.0 times longer than wide, attenuate at base, acute to rounded at apex; margins flat, strigillose-ciliate; surfaces sparsely strigillose; several orders of venation evident. Reduced dichasia solitary or opposite at the nodes, sessile (rarely short pedunculate, the peduncles to 2 mm long) in leaf axils or in axils of bracts on a helicoid or scorpioid spicate axis to 5 cm long; flowers 1-3 per dichasium, each sessile or short (to 0.5 mm long) pedicellate, subtended by 2 bractlets. Bracts (if present) narrowly elliptic to linear, 2-7 mm long, 0.3-1.0 mm wide, pubescent like leaves. Bractlets subulate to narrowly lanceolate, 1.0-3.5 mm long, 0.2-0.6 mm wide, pubescent like leaves. Secondary bractlets (if present) subulate, 0.8-1.6 mm long, 0.2 mm wide. Calyx 3-5 mm long, the outer surface pubescent like leaves, the inner surface sericeous with appressed trichomes to 0.3 mm long; tube 1.0-1.5 mm long; lobes subulate, 2-4 mm long, 0.5-0.7 mm wide at base. Corolla bilabiate, light or dark blue (rarely pinkish) with a papillate, yellow eye streaked with purple veins on the upper lip, 6.5-9.0 mm long, pubescent on the outer surface with erect to flexuose trichomes 0.1-0.2 mm long; tube 2.0-2.8 mm long, 1.0-1.5 mm in diameter; upper lip obovate to spatulate, 3.5-6.5 mm long, 1.5-2.5 mm wide, emarginate at apex; lower lip 4.5-6.5 mm long, the lateral lobes spreading or horizontally oriented, oblanceolate to elliptic, 4-6 mm long, 1.5-2.5 mm wide, the lower lobe oblanceolate, conduplicate, 4.5-5.5 mm long, 1.5-2.5 mm wide. Stamens 3.8-5.5 mm long; filaments purplish, 3-5 mm long, 0.1-0.2 mm wide at base, pubescent, especially near the base with trichomes 0.05-0.1 mm long; anthers maroon turning black, 0.5-0.8 mm long. Disc 0.3-0.5 mm high. Style 4.0-5.5 mm long, glabrous. Stigma lobes 0.2-0.3 mm long. Capsules 9-12 mm long, glabrous; stipe 3.0-5.5 mm long; heads flattened, 5.5-7.0 mm long (including a terminal beak 0.5-1.0 mm long), 4.0-4.5 mm wide; retinacula 1.5-2.0 mm long. Seeds usually 4 per capsule, flat, obliquely cordate in outline, 3.5-4.0(-5.0) mm long, 3.5-4.0 mm wide, rounded to acute at apex; testa papillose (rarely only slightly so); margins entire to crenulate. Flowering. Carlowrightia mexicana begins to flower in May and continues through October.

  • Discussion

    Discussion. Carlowrightia mexicana was confused with C. arizonica for many years and only recently described (Henrickson & Daniel, 1979). As shown by morphology and the artificial hybridizations, the species is more closely related to several Chihuahuan Desert species than to C. arizonica. It appears to have a close morphological relative in C. lesueurii, and it can readily hybridize with several species.

    The only known Texas specimen of C. mexicana (Correll 34082) differs from the Mexican material in several respects. It has a much closer and finer pubescence on the vegetative organs, the trichomes are closely appressed rather than retrorse, and the seeds are larger (up to 5 mm long) and have consistently smooth surfaces. A collection from east-central Coahuila (Daniel 903) also differs from most specimens of C. mexicana by cauline pubescence which consists of retrorse to flexuose trichomes to 0.5 mm long, light pink corollas often with faint maroon veins on the lateral lobes of the lower lip, and crenate seed margins. In the first two characters, this specimen is intermediate between C. mexicana and C. texana, near which it was found growing. However, neither the high pollen stainability (93%) nor the lanceolate to narrowly elliptic laminar shape of Daniel 903 suggest a recent hybrid origin for these plants compared to the artificially created hybrids between these species, which have a reduced pollen stainability and ovate leaves. The two species may have hybridized in the past, however, and plants such as Daniel 903 may represent backcrosses with C. mexicana. Both of these unusual specimens are included in C. mexicana due to the overlap of most of their characters with those of more typical representatives of the species. Both occur on the edge of the range of the species and considering the effects of isolation on largely inbreeding plants, it does not seem unusual to find minor differences in these peripheral populations.

    In addition to its occurrence with C. texana, C. mexicana has been found growing with C. parvifolia. In two localities in north-central Coahuila, C. mexicana and C. parvifolia were observed growing within several decimeters of one another. Natural hybrids between these species were not found and the artificial hybridizations indicate that they are not capable of hybridizing.

    Distribution and Ecology: This species is known only from the central and eastern regions of the Chihuahuan Desert in Coahuila and adjacent Texas, having been especially well collected in areas north of the Cuatro Ciénegas basin. It becomes locally frequent on dry, rocky flats and especially in consolidated arroyo gravel in desert scrub and oak chaparral at elevations of 1050 to 1410 meters. It is often found in association with species of Brahea, Quercus, Brickellia, Acacia, Dasylirion, Yucca, Opuntia, Fraxinus, and Ptelea.

  • Distribution

    United States of America North America| Texas United States of America North America| Mexico North America| Coahuila Mexico North America|