New localities and floral forms of Stelis zootrophionoides (Orchidaceae) Mexican endemism, and evaluation of its extinction risk

Stelis zootrophionoides (Orchidaceae) was described from a plant collected in the vicinity of San Cristóbal de Las Casas, Chiapas, México. This paper reports the discovery of new localities of S. zootrophionoides and floral forms (based on the color of its flowers) not previously known to science. The potential distribution of the species was modeled and the extinction risk was assessed through Risk Assessment Method of Extinction for plants in México (MER-Plantas). In addition, the population at greatest risk of the species was characterized. Four populations of S. zootrophionoides were discovered. Stelis zootrophionoides is now known from five localities, with a potential distribution area of 292 km2. Two new forms of the species were found, one with purple flowers with white spots and one with yellow-green flowers ("albino"). According to the evaluation of the MER-Plantas, S. zootrophionoides is in danger of extinction (P). The population evaluated is composed by 41 individuals, and is seriously threatened by the habitat degradation and the expansion of urban areas. Demographic and genetic studies of this orchid species are necessary, and to strengthen and implement actions that enable the conservation of its known populations.