Carlowrightia serpyllifolia A.Gray

  • Authority

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

  • Family

    Acanthaceae

  • Scientific Name

    Carlowrightia serpyllifolia A.Gray

  • Type

    Type. Mexico. Coahuila: Hills near Jimulco, 28 Apr 1885, Pringie 218 (GH!, holotype; US!, isotype).

  • Description

    Species Description - Decumbent to erect, globose and intricately branched or lax and openly branched subshrub to shrub to 5 dm high, arising from a woody caudex to 14 mm in diameter or a woody rhizome to 5 mm in diameter. Older stems quadrate to terete or irregularly fissured, 1-3 mm in diameter, pubescent or glabrate. Younger stems green, quadrate to terete, multistriate, 0.5-1.5 mm in diameter, variously pubescent, usually with a mixture of eglandular and glandular trichomes, the eglandular trichomes (absent) sparse to dense, usually concentrated in 2 vertical, often decussate lines, retrorse to erect, 0.05-0.90 mm long, the glandular trichomes (absent) sparse to dense, usually evenly disposed, (0.05-)0.10-0.70 mm long, the nodes usually densely pubescent with tufts of eglandular trichomes, 0.2-0.6 mm long (floccose). Leaves recurved to horizontal to ascendent, subsessile to petiolate; petioles 0.1-7.0(-14.0) mm long, pubescent like the younger stems; laminas (lanceolate) ovate to deltate to orbicular to elliptic to obovate, 2-24 mm long, 1.5-10.0(-16.0) mm wide (reduced in size acropetally into flower-bearing bracts), mostly 0.8-2.8 times longer than wide, attenuate to acute to rounded to truncate at base, acute to rounded at apex; margins entire (rarely minutely undulate), flat, ciliate with glandular and/or eglandular trichomes as on the younger stems; surfaces sparsely to densely pubescent with glandular and/or eglandular trichomes; veins often obscure on the upper laminar surface, 1 or several orders of venation evident on the lower surface. Inflorescence axes usually pubescent with an understory of sparse to dense, erect (retrorse), eglandular trichomes 0.05-0.20(-0.60) mm long (rarely absent), and an overstory of sparse to dense, glandular trichomes 0.1-0.5 mm long. Reduced dichasia usually solitary at the nodes, sessile or rarely pedunculate in the axil of upper leaves or bracts, the peduncles 0.5-2.0(-8.0) mm long; flowers 1-3 per dichasium, each sessile or short (to 1 mm long) pedicellate, subtended by 2 bractlets. Bracts frequently petiolate, (lanceolate) ovate to or-bicular-obovate (triangular), 0.5-2.0(-6.0) mm long, 0.5-1.5(-4.0) mm wide, pubescent like leaves. Bractlets sessile, ovate to subulate, 0.6-2.1 (-4.0) mm long, 0.4-0.8 mm wide, pubescent like bracts. Calyx (1.5-)2.0-4.0(-6.0) mm long, the outer surface pubescent with a mixture of glandular and eglandular trichomes, the inner surface sericeous with appressed, eglandular trichomes 0.2-0.6 mm long; tube 0.5-1.0 mm long; lobes subulate, (1.0-) 1.5-3.5(-5.0) mm long, 0.5-0.6 mm wide at base. Corolla pseudopapilionaceous, (pink-purple) blue-purple with a papillate, yellow eye streaked and fringed with purple veins on the upper lip, 915 mm long, pubescent on the outer surface with trichomes 0.2-0.3 mm long, these frequently restricted to the lower-central lobe; tube 3.0-4.5 mm long, 1.2-2.0 mm in diameter; upper lip spatulate, 7-11 (-14) mm long, 2.8-3.8 mm wide, emarginate at apex; lower lip 7-14 mm long, the lateral lobes obovate-elliptic, (5.5-)7.5-10.0(-13.0) mm long, 3.0-4.5(-6.0) mm wide, the lower lobe conduplicate-keeled, (5.5-)7.0-10.0(-13.0) mm long, 4.0-5.5 mm wide. Stamens 6.5-8.0(—10.5) mm long; filaments purplish, 6.0-7.5(-10.0) mm long, 0.2-0.3 mm wide at base, pubescent, especially near the base, with trichomes 0.05-0.10 mm long; thecae maroon turning black, 0.9-1.2 mm long. Disc 0.3-0.5 mm high. Style 7.5-11.0 mm long, glabrous. Stigma lobes 0.2-0.3 mm long. Capsules 8.7-12.0 mm long, glabrous; stipe 3-5 mm long; head flattened, 5.5-7.0 mm long (including a terminal beak 0.8-1.0 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, 3.5-5.0 mm long, 3-4 mm wide, rounded to acute at apex; testa papillose (rarely only minutely so); margins dentate, the teeth with retrorse barbs. Flowering. Carlowrightia serpyllifolia begins to flower sporadically in February and March, reaches peak-flowering during the months of August through October, and continues to flower into December.

  • Discussion

    Discussion. Carlowrightia serpyllifolia may be readily distinguished from other species of section Pseudopapilionacea by its relatively short (9-15 mm long) corolla which is blue to pinkish within. The ease with which it is capable of hybridizing with species of section Mexicana and its relative inability to be crossed with other species in its own section indicate either that the placement of C. serpyllifolia in section Pseudopapilionacea is artificial, based on the possession of parallel morphological traits, or that strong incompatibility barriers have developed among the species of this section. Since C. glandulosa and C. arizonica also appear to be able to hybridize more successfully with species of other sections than with species of section Pseudopapilionacea, the latter alternative seems more likely.

    Despite its occurrence only within the limits of the Chihuahuan Desert, C. serpyllifolia exhibits considerable variation in certain characters. Figure 21 shows the variation (in each case proceeding from the center of the axis to its periphery) encountered in six collections with respect to leaf length (1-20 mm), corolla length (9-15 mm), calyx length (1-6 mm), and pubescence of the vegetative shoots (nearly eglandular, sparsely glandular, densely glandular). Based on these characters and others, three forms are worthy of note:

    Form 1. This is the most widespread form (represented by polygons a, c, d, and 0- The habit of these plants ranges from decumbent, intricately branched subshrubs with reduced leaves to large-leaved, openly-branched shrubs to 5 dm high. The vegetative shoots are usually densely glandular pubescent; the length of the bractlets ranges from 0.6-2.0 mm; and the length of the corolla ranges from 9-14 mm. The plants tend to be a light, yellow-green color.

    Form 2. In central and western Coahuila, some plants lack, or possess extremely few, glandular trichomes on the vegetative shoots, although they have a glandular inflorescence. They tend to be a dark, olive-green color. In the range of the habit type and in other characters, this form (represented by polygon b) is identical to Form 1.

    Form 3. A third form (represented by polygon e) is known only from the Sierra de Jimulco in extreme southwestern Coahuila. These individuals are large-leaved, openly-branched plants which differ from both Forms 1 and 2 by their long bractlets (2.5 to 4.0 mm long), calyces (4.5-6.0), and corollas (12-15 mm long). Specimens of this form are somewhat intermediate between Forms 1 and 2 in the degree of glandularity of the vegetative shoot. In addition, the trichomes on the inner surface of the calyx are especially well-developed in this form.

    Artificial hybrids between Forms 1 and 2 were less fertile than those within Form 2. Although the percentages of fruit-set and germination of the F, generation were nearly equal for both crosses within Form 2 and between Forms 1 and 2, the percentages of pollen viability (40% vs. 94%), seed-set of the F, generation (56% vs. 78%), and germination of the F2 generation (63% vs. 95%) were considerably lower for the crosses between the forms than for those within Form 2. Hybrids between Forms 1 and 2 have conspicuously glandular vegetative stems. Some of the individuals resulting from crosses within Form 2 possess considerably more glands on the vegetative stems than either of the parent plants.

    Plants of Form 2 grown from seed in a common garden (Daniel 218gh, 221gh) under conditions of less exposure to light and more water than the parents encountered in nature (and collected at the same time of year as plants in the wild), maintained the type of pubescence of their parents, but became larger, more openly-branched plants with larger leaves, longer calyces (to 6 mm long) and longer corollas (to 13.5 mm long). Plants of Form 1 grown in the common garden (Daniel 653gh) react similarly but the changes are less pronounced. This suggests that Form 3 with its more robust habit and larger flowers may be a shade form from a less exposed, possibly moister habitat. Henrickson (pers. comm.) indicates that his collection (13228) came from a shaded limestone canyon.

    The general overlap in the characters used to separate the forms, the presence of numerous individuals intermediate in these characters (numerous specimens from southwestern Coahuila, represented by polygon d and including Pringle’s type collection, are intermediate in pubescence between Forms 1 and 2), and the lack of any discrete geographic or ecologic correlation of the forms (populations of Forms 1 and 2 often occur within 20 meters of each other and both Forms 1 and 3 occur in the Sierra de Jimulco) preclude their formal taxonomic recognition.

    Distribution and Ecology: The species is known only from the Chihuahuan Desert region where it occurs from El Paso, southeastward through the Trans-Pecos region of Texas, and southward through Chihuahua and Coahuila into northeastern Durango and northwestern Zacatecas (Fig. 20). The plants grow in washes on rocky or gravelly hills and along arroyos in desert scrub at elevations of 750 to 1900 meters. Associates include species of Larrea, Agave, Acacia, Fouquieria, Mimosa, Hechtia, Viguiera, Yucca, Cordia, Croton, Opuntia, Euphorbia, Dasylirion, Leucophyllum, Lycium, Karwinskia, Bernardia, Celtis, Cassia, Randia, and Prosopis.

  • Distribution

    United States of America North America| Texas United States of America North America| Mexico North America| Chihuahua Mexico North America| Coahuila Mexico North America| Durango Mexico North America| Zacatecas Mexico North America|