Polystemma leopardum L.O. Alvarado, García-Mend., D. Sandoval & Lozada-Pérez, 2024

Alvarado-Cárdenas, Leonardo O., García-Mendoza, Abisaí Josué, Sandoval-Gutiérrez, Daniel & Lozada-Pérez, Lucio, 2024, A new species of Polystemma (Apocynaceae, Asclepiadoideae, Asclepiadeae, Gonolobineae) from the state of Oaxaca, Mexico, Phytotaxa 649 (1), pp. 111-120 : 113-118

Polystemma leopardum L.O. Alvarado, García-Mend., D. Sandoval & Lozada-Pérez sp. nov. ( Figures 1–4 ).

Diagnosis. Species similar to Polystemma cordatum in having campanulate flowers with long trichomes on the corolla lobes and similar corona appendages; Polystemma leopardum differs by its yellowish flowers with a reticulate purple to black pattern, ovate-lanceolate corolla lobes, internal gynostegial corona with four small teeth between and below the linear-lanceolate appendages, and a convex stylar head (vs. red flowers with a reticulate black pattern, internal gynostegial corona with zero, one or two teeth between the linear-lanceolate appendages and flat stylar head in P. cordatum ).

Type:— MEXICO. Oaxaca: Distrito Tlaxiaco, Municipio San Juan Teita, 200 m al E de San Juan Teita, cerro del Panteón 1466 m, 17°05’32.51’’N, 97°24’33.59’’W, 8 August 2022, D. Sandoval-Gutiérrez & C. Flores-Fausto 1547 (holotype: MEXU, isotypes: IEB, FCME, MEXU, MO, OAX, to be distributed).

Twining plants with white latex. Stems becoming suberous with age, cylindrical with a mixed indumentum of short simple and glandular trichomes densely pubescent, large simple trichomes sparsely pubescent. Leaves opposite, petiole 2.5–3.5 cm long, with indumentum similar to the stem; leaf blade 3–5.5 × 2–3.8 cm, ovate, apex acute to broadly acuminate, base cordate, lobes 3.3–5.3 × 7–14 mm, sparsely to densely pubescent adaxially, glandular trichomes absent, densely pubescent mainly on the midveins and secondary veins abaxially; colleters at the base of the midvein adaxially, 4–6. Inflorescences extra-axillary, one per node, racemiform; peduncle 2–3.9 cm long, with indumentum similar to the stem; bracts 4–6.6 × 0.9–1 mm, linear to lanceolate; pedicel 1.4–2.3 cm long. Calyx green, 5-lobulate, lobes 7–8 × 2–3 mm, lanceolate to elliptic–lanceolate, densely pubescent abaxially. Corolla campanulate, 2–2.5 cm in diameter, yellowish with black or dark purple coloration in the tube, with a reticulate pattern on the lobes, tube 4.9–6 mm long, lobes 5–8.2 × 5–6.8 mm, ovate-lanceolate, apex acute, barbate adaxially, with eglandular trichomes 2.5–3.0 mm long; gynostegial corona adnate at the union of the gynostegium and corolla; external corona dark yellow to yellowish at the base, dark purple to black towards the tip, formed by 5 lobes opposite to the anthers, fused laterally, each lobe with two apical, linear-lanceolate appendages 2.0– 2.6 mm long, and 1–2 (3) teeth 0.2–0.3 mm long between them and sometimes below them, internal corona with two digitate appendages 0.8–1 mm long, with (2) 4 small teeth ca 0.1 mm long between them, gynostegium with a stipe 0.8–1.1 mm long, style apex convex, obtuse, dark purple to black. Pollinarium with a brown corpuscle, elliptical, pollinia ellipsoid, laterally excavated. Follicles fusiform, 12–15 × 1–1.5 cm, glabrous. Seeds not seen. Figures 1–2 .

Distribution and habitat. Polystemma leopardum is known only from the municipality of San Juan Teita, Tlaxiaco district, Oaxaca, Mexico ( Fig. 3 ). The plants grow on rocky slopes with gypsic soils, at elevations of 1323–1466 m. It inhabits xerophytic scrub and tropical deciduous forest with Agave gypsicola García-Mend. & D.Sandoval in García-Mendoza et al. (2019: 6), Calochortus multicolor García-Mend., D.Sandoval & Chávez-Rendón in García-Mendoza et al. (2023: 3), Cephalocereus parvispinus Arias, Tapia & Guzmán (2019: 150) , Mixtecalia teitaensis García-Mendoza, D.Sandoval & Redonda-Martínez (2020: 128) , Sisyrinchium longispathum Conzatti (1947: 124) , and Xochiquetzallia magnifolia García-Mendoza & Gutiérrez (2022: 202) .

Phenology. Flowering and fruiting are known from June to October.

Conservation status. Individuals are known from only five populations ( Fig. 3 ), such that the area of occupation (AOO) is 8 km 2. It is found in a specialized habitat with gypsic soils, which is affected by livestock grazing similarly to reports in Agave gypsicola García-Mend. & D. Sandoval (2019: 6-9) ( García-Mendoza et al. 2019). Considering that the known distribution is very restricted, with only five populations recorded, and given the anthropogenic impact affecting the habitat, We therefore propose the new species in the category of Endangered (B2abiii).

Etymology. The specific epithet refers to the pattern of yellow coloration with black tones reminiscent of the coloration of the ocelot ( Leopardus pardalis Linnaeus 1758: 42 ), a feline distributed from the southern United States to northern Argentina.

Additional specimens examined:— MEXICO: Oaxaca, distrito Tlaxiaco: municipio San Juan Teita , 1 km NE de San Juan Teita, 1,346 m, 17°05’46.41’’N, 97°24’44.92’’W, 8 August 2019, A. García-Mendoza et al. 11412 ( MEXU) ; Kava xikití [Peña de espalda delgada], 1 km SE de San Juan Teita, 1,350 m, 17°5’48.26’’N, 97°24’43.7’’W, 10 June 2018, A. López Santiago & I. Santiago-Cruz. 149 ( MEXU) ; Ladoxuu 1 km E de San Juan Teita, 1,323 m, 17°05’48.26’’N, 97°24’44.2’’W, 28 August 2019, A. López Santiago & I. Santiago-Cruz 555 ( MEXU) ; Tiko ‘do ñuu, 2 km E de San Juan Teita, 1,353 m, 17°05’48.11’’N, 97°24’44.02’’W, 1 October 2019, A. López Santiago & I. Santiago-Cruz 571 ( MEXU) .

Taxonomic remarks. The species proposed here shares the attributes of the genus Polystemma and is distinguished from the rest of the species by its flowers, which present a distinct pattern of coloration within the group ( Fig. 1–2 ). The recognition of this new taxon increases the number of species for the country to eleven ( Table 1 ) with an endemism of 75 %. These results reaffirm the country as the center of diversity for the genus and family. Polystemma cordatum is the species with the strongest similarity to the species proposed here ( Fig. 4 ), which differs in the coloration and size of the flower as well as the shape of the gynostegial corona and the stylar head ( Juárez-Jaimes & Lozada-Pérez 2003), ( Table 2 ). This morphological difference between the individuals of the two species hypotheses is consistent with the proposed phenotypic restriction laid out in the explanatory hypothesis.

Unlike Polystemma cordatum , which is distributed in calcic soils, the new species is strictly gypsophilic, similar to other species described in the zone, such as Agave gypsicola , Cephalocereus parvispinus , Mixtecalia teitaensis and Xochiquetzallia magnifolia (Arias-Montes et al. 2019; García-Mendoza et al. 2019, 2023; García-Mendoza & Gutiérrez 2022). According to Ortiz-Brunel et al. (2023), Polystemma leopardum represents the first record in the family Apocynaceae of a strictly gypsophilous species for Mexico, such that it also represents an advancement of the knowledge of the species of this genus in the country. Finally, this discovery corroborates the need to establish strategies for the conservation of this edaphic assemblage, which contains numerous species of irreplaceable character in the state.

Figures

FIGURE 1. Polystemma leopardum A. Branch segment with inflorescence and flower bud. B. Detail of stem pubescence. C. Detail of leaf base with colleters. D. Flower. E. Gynostegium and gynostegial corona. F. Detail of the lobe of the gynostegial corona G. Pollinarium. H. Fruit. Illustration by Ericka Belén Cortez Castro, based on the holotype.

FIGURE 2. Polystemma leopardum A. Habitat. B. Plant climbing. C. Detail of suberous stem. D. Leaves and flowers. E. Top view of flower and bud. F. Lateral view of flower. G. Gynostegium and gynostegial corona. H. Fruit. Photograph credits A–F Abisaí García-Mendoza, G–H Abigail López Santiago.

FIGURE 3. Known geographical distributions of Polystemma cordatum and P. leopardum.

FIGURE 4. Morphologically similar species. A–D. Polystemma cordatum. A. Branch with flowers of the type. B–C. Different views of the flowers of the type. D. Detail of the gynostegium. E–H. Polystemma leopardum. E. Branch with flowers of the type. F. Detail of the gynostegium. G. Section of the flower. H. Detail of the gynostegium. Photograph credits: A–C Holotype specimen, Purpus 3836 (UC124986!), D. Illustration by Elvia Esparza, Flora de TehuacánCuicatlán (Juárez-Jaimes & Lozada 2003), E–G. Specimen type H. Illustration by Ericka Belén Cortez Castro, based on the holotype.