Louteridium brevicalyx A. Richardson, Tulane Stud. Zoo. Bot.

Daniel, Thomas F. & Tripp, Erin A., 2018, Louteridium (Acanthaceae: Acanthoideae: Ruellieae: Trichantherinae): Taxonomy, Phylogeny, Reproductive Biology, and Conservation, Proceedings of the California Academy of Sciences 65 (2), pp. 41-106 : 71-72

1. Louteridium brevicalyx A. Richardson, Tulane Stud. Zoo. Bot. 17:66. 1972. TYPE.— MEXICO. Michoacán: Distr. Coalcomán, Aquila [ca. 18°35’49.39”N, 103°30’14.64”W], 200 m, 21-III-1941 (flr, frt), G . Hinton et al. 15825 (holotype: US!; isotype: NY!) .

Trees to 8 m tall, mostly epipetric. Older (woody) stems subquadrate to terete, irregularly fissured, sometimes ± scurfy, often lenticellate, lacking trichomes; younger (herbaceous) stems terete (when fresh), becoming flattened on drying, sparsely lenticellate, irregularly fissured, lacking trichomes. Leaves seasonally deciduous, clustered at shoot apex, petiolate, petioles to 90 mm long, sometimes tinged with pink or red, blades subsucculent, narrowly ovate to ovate to elliptic, 85–157 mm long, 31–76 mm wide, 1.8–2.7 × longer than wide, acute to acuminate at apex, acute to attenuate at base, surfaces glabrous (or rarely with very few scattered flexuose eglandular trichomes mostly on veins on abaxial surface, the trichomes especially evident on immature leaves), midvein sometimes pinkish to reddish purple (especially adaxially), margin entire. Inflorescence a terminal sessile or pedunculate thyrse to 38 cm long (including peduncle, if present, and excluding corollas), peduncle (if present) pubescent with erect to flexuose glandular trichomes 0.05– 0.7 mm long (glandular pubescent), rachis glandular pubescent and often with scattered erect to flexuose eglandular trichomes to 0.7 mm long as well; dichasia opposite or alternate, pedunculate, 1–many-flowered, to 120 mm long (excluding corollas), dichasial peduncles 15–60 mm long, pubescent like rachises. Bracts caducous (rarely present), lanceolate to lance-ovate, 6.5–7. 5 mm long, 2.5– 2.8 mm wide, abaxially pubescent like rachis (except sometimes with more eglandular trichomes). Bracteoles and secondary bracteoles caducous, lance-subulate to linear to ovate-elliptic, 2–7 mm long, 0.9– 2 mm wide, abaxially pubescent like rachis or with more eglandular trichomes. Flowers pedicellate, pedicels 25–50 mm long, glandular pubescent. Calyx 10–16 mm long, lobes fused at base for 1.5– 3 mm, subhomomorphic to subheteromorphic, membranaceous, lanceolate to ovate, 7. 5–12 mm long, 3–7 mm wide, subequal or with posterior lobe either slightly larger or smaller than lateral lobes, acute at apex, abaxially pubescent with erect to flexuose glandular and eglandular trichomes 0.05– 0.3 mm long, posterior lobe subplanar to subconduplicate. Corollas greenish, 35–65 mm long, externally pubescent with erect to flexuose glandular and eglandular trichomes 0.05– 0.3 mm long, tube 25–30 mm long, narrow proximal portion 7–12 mm long, 7–11 mm in diameter near midpoint, throat 15–25 mm long, 26–30 mm in diameter at mouth, lobes spreading to recoiled, ovate to subcircular, 15–24 mm long, 16–24 mm wide, rounded and emarginate at apex. Stamens 4, 65–80 mm long, filaments distally glabrous, pubescent with eglandular trichomes near base, thecae 8–11 mm long; staminode 0. Style 75–77 mm long, glabrous distally, pubescent near base with eglandular trichomes, stigma subequally 2-lobed and ± funnelform, lobes elliptic to subspheric, 2–3 mm long, 1.5– 3 mm wide. Capsules 32–42 mm long, 6–9. 5 mm in diameter, pubescent with erect to flexuose eglandular and subsessile to stipitate glandular trichomes less than 0.05– 0.4 mm long, stipe 2–5. 2 mm long. Seeds 16–24 per capsule, 5. 5–7 mm long, 4. 5–6 mm wide, surfaces smooth.

PHENOLOGY.— Flowering: March; fruiting: March. Field observations on Daniel & Steinmann 11913 reveal that no flowers were open between 16:00–17:30 on the first day of observations, but several very large floral buds were present. On the following day, all of the large buds were found to be fully open at 08:30, and no visitors were noted over the course of an hour.

DISTRIBUTION AND HABITAT.— West-central Mexico (Michoacán; Fig. 8 ); plants occur on exposed limestone, often on steep slopes of arroyos, in tropical subdeciduous forests at elevations from 200 to 590 meters.

ILLUSTRATIONS.— Figure 2A–E; Richardson (1972:66, fig. 2).

CONSERVATION.— Except for L. rzedowskianum , which is known from a single site, L. brevicalyx has the smallest known EOO (0.27 km 2) among its congeners. At the site of Daniel & Steinmann 11913, about 100 plants were seen growing, mostly epipetrically, in an area of ca. 5000 m 2 on exposed limestone slopes in forest. No protected land appears to be within the species EOO. Evident threats to this species appear to be large-scale mining in the vicinity of Daniel & Steinmann 11913 (ca. 1.5 km distant) and deforestation for agriculture (including cattle) that is evident within the small EOO and in adjacent regions. Given the size of the EOO and apparent major threat (i.e., deforestation for agriculture), a single location is evident. A preliminary conservation assessment of Critically Endangered (CR; B1, a, b; IUCN 2017) is proposed for L. brevicalyx .

DISCUSSION.— Leaves are absent on the field specimens examined. Information on young stems and leaves provided above is from cultivated plants (Daniel & Steinmann 11913cv). Leaves of these plants may not have attained the maximum size encountered in natural settings. The inflorescence, which appears before the leaves, arises from the apex of the previous season’s woody growth and bears a stalked (pedunculate) thyrse or a sessile rachis subtended by axillary dichasia (sessile thyrse). A stem forms with the flush of new clustered leaves later in the season.

Most calyces have the three lobes that are characteristic of the genus. Five lobes with three prominent lobes and two reduced lobes are evident on Hinton et al. 15843; the reduced lobes are 3 to 6 mm long and 0.8 to 2 mm wide. Five-lobed calyces in inflorescences are likely teratological and suggest suppression rather than fusion of lobes for typical plants with three-lobed calyces.

ADDITIONAL SPECIMENS EXAMINED. — MEXICO. Michoacán: Mpio. Aquila, KM 6 .7 carretera Aquila–Coalcomán , 18°36’38”N, 103°28’32”W, P. Carillo-Reyes & V. Steinmann 5484 ( CAS, RSA); between Coalcomán and Aquila , 5.6 km NE of Aquila , 18°36’32.54”N, 103°28’31.38”W, T. Daniel & V. Steinmann 11913 ( CAS, COLO, MEXU, MO, NY, US) , cultivat- ed plants of this collection grown from seed in San Francisco, California, 11913cv (CAS); Aquila [ca. 18°35’49.39”N, 103°30’14.64”W], G. Hinton et al. 15843 ( RSA, US) .

Figures

FIGURE 8. Map of Mexico (showing states) and northern Central America with distributions of species of Louteridium endemic to Mexico: L. brevicalyx, L. dendropilosum, L. koelzii, L. parayi, L. rzedowskianum, and L. tamaulipense. Sym- bols may pertain to multiple collections.