Marsdenia calichicola Carnevali & Juárez-Jaimes, 2016

Carnevali, Germán, Trejo-Torres, Jorge Carlos, Juárez-Jaimes, Verónica, Duno, Rodrigo, Tapia-Muñoz, José Luis, Ramírez-Morillo, Ivón M. & Cetzal-Ix, William, 2016, Marsdenia calichicola (Apocynaceae), a narrow endemic, endangered new species from the Mexican Yucatan Peninsula, Phytotaxa 270 (2), pp. 146-154 : 148-150

Marsdenia calichicola Carnevali & Juárez-Jaimes , sp. nov. ( Figs. 1 , 2 )

Similar to M. trivirgulata but the corolla is rotate (vs. campanulate), pubescent adaxially (vs. glabrous), glabrous or glabrescent abaxially (vs. puberulent), the callous cushions are transversely elliptic, densely pubescent, broader than long (vs. longer than wide, pubescent), and the stylar appendix is proportionally longer and apically sigmoid (vs. straight).

Type:― MEXICO. Yucatán: Municipio Chicxulub Pueblo , camino blanco entre Rancho Chenwayum y Rancho San Antonio, ubicado a unos 9 km al S del desvío de la carretera Progreso-Telchac a lo largo de la carretera Chicxulub Puerto-Chicxulub Pueblo ; partiendo del desvío son 2.79 km al E y luego 1.17 km al N, 21°14’9.47”N, 89° 32’0.62”W, 5–8 m.s.n.m., selva baja caducifolia con abundancia de cactáceas columnares y muchas leguminosas espinosas sobre suelos someros y afloramientos de rocas calizas, [unpaved road between Chenwayum and Rancho San Antonio, about 9 km south of turnoff from the Chicxulub Puerto-Chicxulub Pueblo highway; 2.79 km E from turnoff, then 1.17 km N, 21°14’9.47”N, 89° 32’0.62”W, 5–8 m above sea level, low caducifolious forest with many columnar cacti and spiny legumes over shallow soils and limestone outcrops], 6 November 2008, G. Carnevali, R. Duno, J. C. Trejo & D. Angulo 7394 (holotype CICY!; isotypes MEXU!, MO!) .

Twining or basally subprostrate vines with white latex, heliophilous. Stems basally glabrous or glabrescent, brown, subwoody and corky-suberous, often rooting upon contacting the topsoil layer, eventually yielding new ramets; young branches retrorse-puberulent with simple hairs 0.2–0.4 mm long, these arranged in irregular longitudinal bands. Leaves opposite, blades 3.0–4.5 × 1.5–2.4 cm, elliptic to widely elliptic, apex acute to abruptly acuminate, more rarely obtuse to broadly obtuse, margin entire, base acute-cuneate, adaxial surface dark green, sparsely strigulose, abaxial surface paler green, more sparsely strigulose, lateral veins sulcate, 3–4 pairs emerging at an angle of ca. 45° relative to the midnerve, laxly provided with long pale green hairs, conical colleters 2 at adaxial base of midrib, ca. 0.5 mm long; petioles 3–6(–8) mm long, sulcate ventrally, with ubiquitous pubescence but denser toward the bases, consisting of 0.2–0.4 mm long hairs. Inflorescences axillary, one per node, an umbelliform cyme, 4–8-flowered, with 2–3 clustered flowers facing different directions open simultaneously; peduncle ca. 2 mm long, slightly and irregularly puberulent, the pubescence ubiquitous but denser toward the base, hairs 0.2–0.4 mm long, pedicels 1–2 mm long; bracts 0.8–1.1 mm long, one per flower, ovate, apex acute, slightly and irregularly puberulent. Flowers relatively showy, calyx shorter than the corolla tube, lobes 2.4–2.6 × 1.2–1.4 mm, ovate to ovate elliptic, dextrosely imbricate, apex broadly obtuse, abaxial surface glabrescent or slightly and irregularly puberulent, margin ciliolate, colleters 2 per sinus, conical, ca. 0.2 mm long; corolla white with 3–4 reddish longitudinal bands in the basal half of each lobe, color bands tenuously noticeable on the abaxial surface (the color pattern is obscured in dry material), rotate, 5–6 mm diameter, tube 1.5–2.0 mm long, adaxially glabrous or very sparsely pubescent with the pubescence arising from the throat to the corolla lobes, abaxially glabrous, throat densely pubescent, corolla lobes oblong elliptic, 3.5–4.5 × 1.0– 1.1 mm, apex obtuse to obliquely subtruncate-emarginate, slightly and regularly puberulent in the inner surface, glabrous on the outer surface, margins slightly revolute, sparsely ciliolate, particularly toward the apex; callous cushions of the corolline corona transversely oblong to sub orbicular, located at the sinus of the corolla lobes, densely pubescent; gynostegium 1.8–2.0 mm long (not including the stylar head appendix), sessile, narrowly conical; gynostegial corona 5-lobed, adnate to the stamens only at the very base, covering the basal third of the anther appendages, lobes 0.6–0.7 × 1.1–1.2 mm, apex broadly rounded, concave and thickened marginally, overlapping contiguous lobes and covering the stigmatic surface; anthers 1.3–1.4 × 0.4–0.5 mm, anther membranes triangular-caudate, 0.3–0.4 mm long, apex acute; style head appendix conical, rostrate, sigmoid in the apical half, apex cleft about 1/3 of its length, 2.2–2.3 mm long; corpuscle oblong, ca. 0.2 × 0.05 mm, straight, apex rounded; pollinia ca. 0.25 × 0.06 mm, narrowly obovate-reniform, caudicles ca. 0.1 mm long. Follicles unknown.

Etymology:―The specific epithet “ calichicola ” refers to the habit of growing over caliche, the hardened sedimentary rock that outcrops in many places of the northern Yucatan Peninsula and forms a thick, impermeable shell that sustains a xerophytic or sclerophyllous, endemic-rich community. Marsdenia calichicola inhabits this ecosystem, with the basal portion of its stems often trailing and rooting over the naked rock in the shade of shrubs.

Phenology:― Marsdenia calichicola has been observed in flower in October (2011) and November (2008, 2011). When in bloom, 4–10 distal internodes per branch flower simultaneously, with a mature plant producing several hundred, faintly and sweetly fragrant flowers. However, in spite of abundant flowers produced, no fruits have been seen to date. Self-sterility has been reported for some species of Asclepias L. ( Wyatt & Lipow 2007); for example, the inability to produce fruits is due to a single gene (Lipow & Wyatt 2010) in Asclepias exaltata L. (1756: 404) a member of the APSA group (a clade consisting of subfamilies Apocynoideae , Periplocoideae , Secamonoideae , and Asclepiadoideae, Livshultz et al. 2007 ) such as the genus Marsdenia . The scarcity of fruits in Marsdenia calichicola is probably related to self-sterility since incompatible systems are usually conserved among closely related taxa ( de Nettancourt, 1977). Similarly, Acevedo (1999) reported the case of Marsdenia woodburyana Acevedo (1999: 167) , a rare endemic from calcareous, coastal areas in Puerto Rico that similarly flowers sporadically and fruits rarely. Perhaps this phenological strategy is shared by other Marsdenia species growing in such habitats. In our experience with M. calichicola , no insects have been observed visiting the flowers or feeding on the vegetative portions. The plants are partially to totally deciduous during the peak of the dry season (late March–early June). In cultivation, with regular watering, most leaves are retained throughout the year. The species is readily propagated by means of rooted stolons, and several plants are already under cultivation at the Jardín Botánico Regional “Roger Orellana”, at CICY, and in a few private collections.

Distribution and Ecology:― Marsdenia calichicola is restricted to a narrow fringe of very specialized habitat ( Fig. 3 ). It is found only along the northernmost edge of an ecosystem characterized by the outcropping of a thick limestone slab, the caliche, which is variously eroded and covered partially by a thin layer of organic soil. This narrow strip of caliche is located from just a few hundred meters up to a few kilometers from the coast. This ecosystem has been called “selva baja caducifolia con cactáceas columnares” (low deciduous forest with columnar cacti, see Olmsted et al. 1999 for a characterization and Carnevali et al. 2003 for a brief discussion of its phytogeography). It harbors a specialized flora along with a mosaic of vegetation types adapted to high temperatures and severe seasonal drought. In fact, a relatively high number of the phytotaxa endemic to the YPBP seem to occur here ( Carnevali et al. 2003) mainly because it constitutes an island of dry vegetation types surrounded by the sea or by moister plant associations to the south. To find other areas supporting these or equivalent vegetation types, a traveler would have to go the Chiapas Central Depression (650–700 km in a straight line to the SW) or to central Veracruz (800–850 km to the WSW), where similar plant associations occur.

At the type locality, M. calichicola grows along with other restricted, critically endangered endemics such as Ipomoea sororia Austin & Tapia-Muñoz (2001: 807) , Wimmeria obtusifolia Standley (1930: 20) , Zephyranthes orellanae Carnevali, Tapia-Muñoz & Duno (in Carnevali et al. 2010a: 45), and several species of Cactaceae .

Discussion:―On account of its compact inflorescences, shortly tubed corollas, lobes of the staminal corona not surpassing the anthers, and elongated stylar appendix, Marsdenia calichicola belongs to Marsdenia section Rostratae Rothe (1915: 425) . Within the section, it is further referred to subsection Edules ( Rothe 1915: 425) because of the corolla lobes much longer than the corolla tube ( Rothe 1915, Juárez-Jaimes & Alvarado-Cárdenas 2010). Within subsection Edules , M. calichicola belongs in a complex of three very similar, yet distinct species that include M. gallardoae Lozada-Pérez (2000: 128) , from the Tehuantepec Isthmus area and contiguous Chiapas, and M. trivirgulata Bartlett (1909: 632) , which ranges widely along the Pacific watershed from Sinaloa to Panama. This group of species referred to as the Marsdenia trivirgulata complex is characterized by small, ovate-elliptic leaves, short, densely flowered, subumbellate cymes, and basically white corollas with longitudinal red or red-purple stripes; all three species occur in tropical seasonally dry forests (“selva baja caducifolia”) at elevations below 500 m (rarely up to 800 m).

Marsdenia calichicola is most similar and probably most closely related to M. trivirgulata from which it is easily distinguished, among other characters, by its densely pubescent corolla, ovate calyx lobes (vs. elliptic in M. trivirgulata ) and the apically sigmoid stylar appendix (vs. straight). From M. gallardoae , which also features an internally pubescent corolla, the novelty presented here is easily diagnosable by the conspicuous cushion-like calli composing the corolline corona, which are absent from M. gallardoae and the 4–8 flowered inflorescences (2–4-flowered in M. gallardoae ) The three species can be most easily distinguished by the following key, which includes additional characters:

Figures

FIGURE 1. Marsdenia calichicola Carnevali & Juárez-Jaimes (based on Carnevali et al. 739, CICY, MEXU, MO; all photograps by Germán Carnevali). A. Flowering plant. B. Inflorescence featuring flowers at anthesis, one in front view; note corolla color pattern. C. Inflorescence with flowers in anthesis in lateral view. D. Front view of partially disassembled flower; note pubescent calli at base of the corolla lobes (arrowed). E. Lateral view of partially disassembled flower showing apical portion of gynostegium; note sigmoid stylar appendix (arrowed).

FIGURE 2. Marsdenia calichicola, flower details (based on Carnevali et al. 739, CICY, MEXU, MO; line drawings by Alberto Guerra). A. Flower at anthesis, lateral view. A1. Calyx, A2. Corolla. A3. Stylar appendix. B. Spread corolla, featuring shape of the corolla lobes and position, shape, and pubescence of the calli. B1. spread corolla. B2. cushion-like calli. C. Gynostegium, lateral view, featuring shapes and relative sizes and position of the corona lobes, the anther appendices, and the sigmoid stylar appendix. C1. Anther appendice, C2. sigmoid stylar appendix

FIGURE 3. Distribution of Marsdenia species in the Yucatan Peninsula Biotic Province.