Ruehssia sumiderensis Lozada-Perez, sp. nov.
Creators: name: Lozada-Pérez, Lucio
name: Ramírez-Marcial, Neptalí
name: Martínez, César Adrián González-
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Gentianales
Apocynaceae
Ruehssia
Ruehssia sumiderensis

description: Ruehssia sumiderensis Lozada-Pérez, Ramírez-M., Gonz.-Martínez, sp. nov. (Figs. 1–3)
Type:— MEXICO. Chiapas: Tuxtla Gutiérrez, Parque Nacional Cañón del Sumidero, camino hacia Tierra Colorada, arriba del campamento Momotus II, 1290 m, 16°49’53.61’’ N, 93°04’46.55’’ W, 22 Sep 2018 (fl.) N. Ramírez-Marcial 1217 (holotype: CH!; isotypes: CHIP!, HEM!, MEXU!).
Diagnosis:— Ruehssia sumiderensis is akin to R. laxiflora and R. pinetorum for presenting non-cordate lamina base, a lax inflorescences, and corolla without fleshy callous in the sinuses, but differs by the umbelliform lax inflorescences (vs. lax paniculiform ones); corona with convex lobes (vs. sagittate, slightly dentate in R. laxiflora, and laminar, bent towards the anthers in R. pinetorum).
Description:— Plants climbing; roots not seen; stems semi-woody with corked base and with ribs on the distal branches (Figs. 1A, 2A–C), smooth with lenticels, young branches tomentose in two lines, retrorse trichomes; latex transparent. Leaves ovate, elliptic to oblong-elliptic, blades 3.5–7 × 1.5–3 cm, apex acuminate, obtuse to acute, base rounded to truncate, ciliolate, more densely towards the base and progressively less towards the apex, adaxial surface dark green, very sparsely puberulent, abaxial surface pale green, glabrate, 4–6 lateral veins, 4 or 5 colleters at the base of the blade on the midvein (Figs. 1A, 2D–E); petioles 1–2 cm long, canaliculate, puberulent on the margins of the canal. Inflorescence umbelliform, extra-axillary, one per node, simple and lax, up to 8 flowers per inflorescence, but only 1 or 2 flowers persist at anthesis; peduncles 1.3–2.7 cm long, glabrate; pedicels 1–2 cm long, glabrate; bracts broadly ovate, 0.5–0.7 × 0.6–0.8 mm, apex acute, glabrate (Figs. 1A, 2F–H); sepals elliptic, 1.4–1.6 × 1.3–1.5 mm, apex rounded, adaxially and abaxially glabrate, margin ciliolate, with 1–3 colleters on each inner sinus; corolla rotate, reticulated, with 3 main parallel lines, red veins, estivation imbricate and dextrorse, abaxially glabrate and adaxially densely puberulent; tube ca. 2 mm long, without fleshy callous cushions in the sinuses, pale red; lobes elliptic, 6–7 × 4.5–5 mm, orange to yellowish, pale red at base, margin slightly thickened and revolute at the distal third, ciliolate, apex obtuse and with a little notch, (Figs. 1B, 2I); staminal corona with 5 convex, papillose, and basally fused lobes, 0.8–1 mm wide, lower than the style-head, upper side connivant to the anthers, dorsally fully fused to the anther, crenulate at the margin, orange to yellowish (Figs. 1D–E, 2I, 3A–E, G–I); gynostegium sessile, white; anthers with an apical rounded membrane, purple, wings of anthers 0.3–0.35 mm, the base with two thickening forming parallel lines that extend over the corona (Figs. 1E, 3H–I); corpuscle ellipsoid 0.28–0.29 × 0.11 mm; caudicles 0.2–0.21 mm long, with a widened area at the site of union with the pollinia; pollinia ellipsoid 0.21–0.25 × 0.1–0.12 mm (Figs. 1C, 3F); apex of style-head flat to slightly convex, shorter than the apical appendage of anthers. Follicle fusiform with an acute tip, immature, glabrate (Fig. 2K).
Etymology:— The specific epithet derives from the name of the Cañón del Sumidero National Park, located in the state of Chiapas, where the cited specimens used for the description of the species were collected.
Phenology:— It flowers from June to October and fructifies in November. Some flowers show florivory at the lobes of the corolla (Fig. 2J). The immature fruits also show frugivory.
Distribution and ecology:— Ruehssia sumiderensis is known only from the Cañón del Sumidero National Park in the state of Chiapas, Mexico (Fig. 4A). This region is located between two physiographic provinces, the Central Depression and the Chiapas Highlands, and is limited by the Northern Mountains (Müllerried 1957), at an elevation from 1100 to 1300 m. It thrives in the tropical semideciduous forest (Fig. 4B–C).
Conservation status:— The Cañón del Sumidero has been an essential region in floristic studies such as Reyes-García & Sousa (1997) and Espinosa-Jiménez et al. (2011), being the latter a study with 2900 registers and a total of 1298 species; the 2.6% is endemic of the state of Chiapas. Ruehssia sumiderensis was discovered in 2017 and had not been previously collected despite the numerous floristic studies in the state. There are four observations of the new species in iNaturalist (inaturalist.org) by NRM representing different populations. The populations are separated from each other by 3 to 5 km. Altogether, up to 25 individuals have been quantified. In 2019, an additional population was destroyed by road repair works inside the Cañón del Sumidero. The AOO is 16 km 2, and the EOO is 2.48 km 2. According to the International Union for Conservation of Nature and Natural Resources (IUCN 2019), the category proposed for the new species is Endangered B2ab(iv).
Additional specimens examined:— MEXICO: Chiapas: Tuxtla Gutiérrez: Parque Nacional Cañón del Sumidero, camino hacia Tierra Colorada, arriba del campamento Momotus II, 16°49’53.61’’ N, 93°04’46.55’’ W, 17 Nov 2018 (fl.), N. Ramírez-Marcial 1230 (CH!).
Remarks:— Although the flower of the new species morphologically resembles Matelea s.l., like Matelea sugillata, it lacks glandular trichomes and pendulous or horizontal pollinia with an apical sterile hyaline region, attributes that characterize the subtribe Gonolobineae of the tribu Asclepiadeae (Endress et al. 2018). In our phylogenetic analyses, we recovered the new species nested in Ruehssia with high posterior probability and bootstrap support (> 0.9/90; Fig. 5). Neverthless, the relationships inside Ruehssia clade have low support (<0.7/70). Ruehssia sumiderensis is morphologically more similar to R. laxiflora and R. pinetorum, two species also from Mesoamerica (Stevens & Morales 2009). They are distinguished because of the non-cordate leaves at the base, lax inflorescences, and rotate corolla, without callous cushions in the sinuses; there are no other species in Mesoamerica showing the combination of these three features. In R. sumiderensis, the inflorescence is a lax umbelliform, not branched, the corolla is pale red and orange-yellowish with reddish veins, densely puberulent adaxially, and the corona has convex lobes. In contrast, the other two species show paniculiform inflorescences, purple, pink, or reddish-brown corolla, adaxially glabrate in R. laxiflora; in R. pinetorum, the corolla is white or pale green with purple spots and adaxially transparent, hispidulous except for a glabrate margin; the corona lobes are sagittate, slightly dentate in R. laxiflora and laminar, bent towards the anthers in R. pinetorum (according to Stevens & Morales 2009).
description: Published as part of Lozada-Pérez, Lucio, Ramírez-Marcial, Neptalí & Martínez, César Adrián González-, 2020, Ruehssia sumiderensis (Apocynaceae), a new species from Chiapas state, Mexico, pp. 69-80 in Phytotaxa 440 (1) on pages 72-75, DOI: 10.11646/phytotaxa.440.1.4, http://zenodo.org/record/13873270