Marsdenia trivirgulata, Bartlett, 1909

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 : 151

Key to the species of the Marsdenia trivirgulata complex

1. Inflorescences with 2−4 flowers open at a time; corolla lacking a corona altogether; lobes of the gynostegial corona longer than wide, cordate, with a broadly rounded apex, covering 2/3 of the anther appendages; stylar appendix minutely bifid at apex; plants from the Tehuantepec Isthmus area and neighboring Chiapas State ............................................................................. M. gallardoae

− Inflorescences with 4−8 flowers open at a time; corolla exhibiting a corona of cushion-like calli; lobes of the gynostegial corona wider than long, subrectangular with a subtruncate apex, covering only the basal ¼ of the anther appendages; stylar appendix deeply bifid at apex; plants from the northern Yucatan Peninsula or from the Pacific watershed from Sinaloa ( Mexico) southward to Panama...........................................................................................................................................................................................2

2. Calyx lobes ovate; corolla white, with 3–4 continuous red stripes restricted to the lower half, rotate, internally densely pubescent, gynostegium 1.8–2.0 mm long; calli of the corolline corona densely pubescent, wider than long; stylar appendix ca. twice as long as the anther appendages, apically sigmoid; corpuscle thicker, ca. 3 times longer than wide, shorter than the pollinia; petioles 5–8 mm long; leaf blades adaxially sparsely strigulose, strigose abaxially; plants from the dry forests over caliche in the extreme NW of the Yucatan Peninsula ................................................................................................................................................ M. calichicola

– Calyx lobes elliptic; corolla white to pale red or purplish, with discontinuous red stripes over all its surface, campanulate, internally glabrous or glabrescent; gynostegium 1.0– 1.5 mm long; calli of the corolla glabrous, longer than wide; stylar appendix ca. 1.2–1.5 times longer than the anther appendages, apically straight; corpuscle very narrow, ca. 7 times longer than wide, as long or longer than the pollinia; petioles 6–10 mm long; leaf blades adaxially glabrescent or with adpressed hairs on the nerves, abaxially sparsely puberulent or with lax hairs on the veins; plants from the Pacific watershed from Sinaloa ( Mexico) southward to Panama............. ...................................................................................................................................................................................... M. trivirgulata