Phaseolus polymorphus Sereno Watson (1882: 346) [clade A; sect. Pedicellati (Benth.) Freytag].

TYPE: JG Schaffner 811 (SYNTYPES: GH-64100, CC Parry & E Palmer 188 (MO-1731110)) .

Just above the original publication of this species, the specimen JG Schaffner 811 is also considered as Phaseolus heterophyllus Willd., that is, Macroptilium gibbosifolium (Ortega) A. Delgado ! As aptly noted by Alfonso Delgado-Salinas (1985, p. 281), the specimen GH-64100 is a mix including P. grayanus . The specimen JG Schaffner 811 kept in Kew (K-478482) consists of (mainly) P.grayanus, possibly a small stem of P. polymorphus and a small blooming stem of P. purpusii to the lower right. The specimen CC Parry & E Palmer 186 kept in Harvard (GH-64101) and in Kew, and also cited as syntype, is P.grayanus, and thus not considered to represent this species. The specimen CC Parry & E Palmer 188 kept in Saint-Louis (MO-1731110) is not a mixture and makes sense for P.polymorphus (different from P. filiformis Benth. and P.wrightii A. Gray sensu 1853) along the brief description provided by Watson. It is a climbing vine displaying heteroblastic development growing in pine-oak mixed forest and oak grassland at 900–2500 m.

Specimens: MEXICO. Chihuahua: J Passini 6654 (ENCB). Coahuila: Henrickson 22501 (ANSM-73568). Nuevo León: J Hinton 23421 (TEX-273397). Tamaulipas: JA Encina 1743 (ANSM-85810). Zacatecas: LA García-R. 758 (IBUG-167893). San Luís Potosí: DG Debouck 2056 (UC-1716191). Guanajuato: DG Debouck 2398 (US-3168517). Queretaro: L Paray 2480 (ENCB). Hidalgo: CA Purpus 1365 (POM-17092). Jalisco: LA García-R.650 (IBUG-163783).

It might be appropriate to finish here with a note about P. scabrellus Bentham ex S. Watson that is described in the same publication (1882: 346–347) just after P. polymorphus (and mentioned in the list of “Vascular Plants of the Americas” (Tropicos 2020)). Sereno Watson referred to two specimens (thus syntypes): Ed Palmer 2122 (GH-64106) and Th Coulter s.n. (GH-64105, K-478484). The author concurs with A. Delgado-Salinas (1985, p. 277) in considering this taxon as synonym of P.pedicellatus . Interestingly, Piper (1926, p. 691) wrote “ Palmer 2122, which really is P.pedicellatus Benth. ”.