Polystemma cualense C. D. Sanchez, S. Islas & A. Black 2026, sp. nov.

This is the authors' abstract. We don't add key points for this paper.

Polystemma cualense C. D. Sánchez, S. Islas & A. Black sp. nov. Fig. 1 Type. Mexico • Jalisco, ejido El Cuale, Talpa de Allende municipality, Los Lobos trail to El Cuale, 20°27'50.3"N, 105°05'39.7"W, 1,030 m, 24 Aug 2024, C. D. Sánchez, A. Black, J. Reyes and M. Peinado 1701 (Holotype: MEXU!; • Isotypes: PV!). Diagnosis. Polystemma cualense resembles P. horconesense in having flowers similar in size and shape. Polystemma cualense differs in having a gynostegial corona higher than the gynostegium (vs. gynostegial corona the same height as the gynostegium), external gynostegial corona lobes 3–4 mm length (vs. 0.5–0.6 mm length) and gynostegium black (vs. gynostegium green-yellowish). Description. Perennial climbing plants. Stems cylindrical, mixed indumentum of long simple trichomes ca. 0.5 mm long oriented along two lines on the sides of the stem, simple short trichomes ca. 0.1 mm long, and glandular trichomes ca. 0.2 mm long, the latter more dense in the nodes. Leaves petiolate, petioles 2.3–5.1 cm long, lamina elliptic-ovate, 5.7–8.8 x 2.8–5.4 cm, base cordate, lobes 6.7–10.5 x 11.3–19.3 mm, apex mucronate, 5–11 mm long, margins entire, ciliate; adaxially with simple trichomes upon the veins, abaxially with glandular trichomes upon the veins; colleters 4–6, at the union of the leaf blade with the petiole, conical to spheroid, 0.3–0.6 mm long, yellowish-brown to dark brown; 3–4 pairs of secondary veins. Inflorescences cymose-umbelliform, one per node, extra-axillary, with 4–6 flowers; peduncles 2.2–3.5 mm long, with mixed indumentum of short simple trichomes and glandular trichomes; bracts two per flower 4.6–5.7 x 1.0–2.0 mm, ovate-lanceolate, with long simple trichomes on the margins. Flowers pentamerous, pedicels 6.5–11.2 mm long with mixed indumentum of long simple trichomes, short simple trichomes, and glandular trichomes; calyx with sepals fused at the base, tube ca. 2.5 mm long, lobes 7.2–10.4 mm x 2.6–3.9 mm, lanceolate, adaxially and abaxially glabrate, margins ciliate, colleter one, ca. 0.4 x 0.3 mm, at the base of the sepals, alternating with them, ovate, yellow; corolla rotate, 2.5–3.5 cm in diameter, deeply lobulate, yellowish-green to yellowish-brown with darker brown reticulum, aestivation valvate in the flower buds, tube 3.4–4.3 x 4.8–6.3 mm, glabrescent, limb 2.9–3.4 mm long, lobes 1.0– 1.6 cm x 3.7–5.4 mm, lanceolate, apex acute, abaxially and adaxially glabrous; gynostegial corona higher than the gynostegium, formed by five lobes 2.7–3.3 mm long, ca. 7.4 mm in diameter, black, fused at the base forming an uninterrupted ring, external corona cyathiform, with interstaminal lobes 3–4 x 3.4 mm, laminar, internal corona verrucose, with margins crenulate to dentate, gynostegium 7.6–8.0 mm in diameter, stipitate, stipite ca. 0.5 mm long; gynoceium bicarpellary, apocarpous, glabrous, ca. 3.0 mm long, stylar head flat, ca. 2.5 mm in diameter; androecium with anthers horizontal, ca. 0.6 x 1.0 mm, terminal appendages of anthers suborbicular, ca. 1.5 mm; pollinaria with corpuscles 0.25–0.34 x 0.28– 0.28 mm, sagittate, translator 0.24–0.38 mm long, with winged appendages, pollinia 0.52–0.63 x 0.50–0.59 mm, reniform. Immature follicles 9–10.1 x 1–1.1 cm; seeds not seen. Distribution and habitat. Polystemma cualense is endemic to the state of Jalisco, growing in ruderal vegetation and relict gallery forest near crop areas in the Talpa de Allende municipality at 1,030 –1,300 m altitude (Fig. 2). It is associated with Mimosa albida Humb. & Bonpl. ex Willd. (Fabaceae), Hamelia xorullensis Kunth (Rubiaceae), Melampodium perfoliatum (Cav.) Kunth (Asteraceae), Milleria quinqueflora L. (Asteraceae), Adiantum sp. (Pteridaceae), naturalized Bauhinia variegata L. (Fabaceae), and Lantana camara L. (Verbenaceae). Phenology. Flowering occurs from late July through early September, and mature fruits have been observed in September but have not been collected. Conservation status. This species is known only from two populations in Talpa de Allende, Jalisco, with an AOO of 8 km 2 (B 2). In 2025, the only three individuals at the type locality were lost to land clearing (A 1, C 1, and C 2), and the remaining habitats are threatened by deforestation, livestock grazing, and agriculture. Despite the potential for undiscovered populations, a Critically Endangered (CR) status (B 1 + B 2) is recommended to facilitate urgent conservation. Etymology. The name refers to Sierra El Cuale, as the localities of this new species are situated along the margin of this geological formation. This discovery adds to the list of species named in honor of this enigmatic mountain range, whose forests are threatened by land-use change, illegal logging, mining, and fires. iNaturalist records. Mexico: Jalisco, municipality: Talpa de Allende, 20.2114601133, -104.7813415525, 1070 m, 31 Aug 2019, pcarreyes 90622325 (https://mexico.inaturalist.org/observations/97517086). Taxonomic remarks. Exploratory work across the country has led to the description of new species of the genus Polystemma in recent years (Alvarado-Cárdenas et al. 2024 b). This species shares similarities with P. horconesense, as both have flowers of similar corolla size and shape (Fig. 3). Polystemma cualense has umbellate-cymose inflorescences (vs. monochasial inflorescences in P. horconesense), a single colleter at the base of the sepals (vs. three), a rotate corolla (vs. a campanulate-rotate corolla), yellow flowers (vs. brown or pale greenish flowers with violet hues), and a gynostegial corona that extends beyond the gynostegium (vs. a gynostegial corona of the same height as the gynostegium) (Alvarado-Cárdenas et al. 2024 a). These phenotypic differences support the two taxa as hypotheses of distinct species. Polystemma distribution is concentrated primarily on the Atlantic slope, with the western part of the country being an area of high diversity. The Jalisco region is distinguished by its remarkable endemism and recent additions to the state’s flora (Gudiño-Cano et al. 2024), a diversity closely tied to strong environmental heterogeneity along elevation gradients. Polystemma cualense occurs above 1,000 m in temperate subhumid conditions, whereas P. horconesense is restricted to elevations below 400 m in warm subhumid climates. This new taxon increases the number of Polystemma species in Jalisco to 10, which places it among the richest states in this genus, along with Oaxaca (10 species), Guerrero (eight species), and Michoacán (seven species).