Phaseolus chiapasanus Piper (1921: 41) [clade A; sect. Chiapasana A. Delgado].

TYPE: CA Purpus 6881 (HOLOTYPE: US-567182; ISOTYPES: F-415699, GH-64086, NY-26707, UC-172989).

This species stands alone in the genus because the large size of flowers, pods and seeds, and the black color of all plant parts upon drying. Its range at 700–1700 m goes beyond Chiapas, raising the question whether it enters into western Guatemala. Its lower montane deciduous forest habitat is shrinking because of the progress of coffee plantations (Rzedowski 1978).

Specimens: MEXICO. Chiapas: M Sousa-Sánchez 11410 (CAS-676163). Oaxaca: A Flores-Martínez 1685 (IEB-79142). Veracruz: S Avendano 554 (F-1974958).