Tuesday, June 2, 2020

[Botany • 2020] Ruehssia sumiderensis (Apocynaceae: Asclepiadoideae) • A New Species from Chiapas state, Mexico

Ruehssia sumiderensis  Lozada-Pérez, Ramírez-M., Gonz.-Martínez

in Lozada-Pérez, Ramírez-Marcial & González-Martínez, 2020. 

It is herein presented Ruehssia sumiderensis as a new species known only in the Cañón del Sumidero National Park, in Chiapas, Mexico. It is illustrated with a line drawing, live images and SEM photographs of the gynostegium and pollinarium. Morphological and molecular evidence with plastid data (trnL intron and trnL-F intergenic spacer) confirms its position in Ruehssia, a recently proposed genus that includes American Marsdenieae species. It is similar to Marsdenia laxiflora and M. pinetorum due to the basally rounded or truncate leaves, rotate corolla without callous cushions in the sinuses. Two new combinations are also made in Ruehssia, for M. laxiflora and M. pinetorum.

Keywords: Asclepiadoideae; Cañón del Sumidero; Marsdenieae; molecular phylogeny; SEM; Eudicots

FIGURE 1. Ruehssia sumiderensis  Lozada-Pérez, Ramírez-M., Gonz.-Martínez.
A. Branch with leaves and inflorescence; B. Flower, seen from above and under, respectively; C. Staminal corona, seen from above; D. Staminal corona, lateral view; E. Pollinarium
(Illustrated by César Adrián González Martínez from the holotype).

FIGURE 2. Ruehssia sumiderensis  Lozada-Pérez, Ramírez-M., Gonz.-Martínez.
 A. The base of the stem; B–D. Habit; E–H. Inflorescence; I. Ventral view of the corolla and corona (dorsal view of the corolla in the square); J. Florivory at the margin of the corolla; K. Immature follicle; bar 1 cm in A–J.

Ruehssia sumiderensis Lozada-Pérez, Ramírez-M., Gonz.-Martínez, sp. nov. 

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).

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. 

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).

FIGURE 4. Geographic distribution of Ruehssia sumiderensis. B, C. Tropical semideciduous forest.

FIGURE 4. Geographic distribution of Ruehssia sumiderensis. A. Map of geographic distribution.

Lucio Lozada-Pérez, Neptalí Ramírez-Marcial and Sar Adrián González-Martínez. 2020. Ruehssia sumiderensis (Apocynaceae), A New Species from Chiapas state, Mexico. Phytotaxa. 440(1); 69–80.  DOI: 10.11646/phytotaxa.440.1.4