Morphological and anatomical analyses clarify the species definition of Ceratozamia latifolia Miq. (Zamiaceae) and lead to the description of a new species: Ceratozamia reesii

The cycad Ceratozamia latifolia was first described by Miquel in 1847 based on plant of unknown provenance cultivated in Hortus Botanicus in Amsterdam which was obtained from Belgium, and for which no type specimen was collected or preserved. The description was based on a juvenile plant, lacked a detailed explanation of the species’ characteristics, and had no accompanying illustrations. Since then, the concept of C. latifolia long time remained as a nomen dubium, often referring to a species probably from Veracruz, Mexico. However, the neotypification of C. latifolia in 1986 linked the poor description of C. latifolia to a known population from San Luis Potosí (SLP), Mexico. This neotypification brought complications to the taxonomy of the genus: 1) Because the neotype population belonged to the then recently described species C. microstrobila, C. microstrobila fell into synonymy with C. latifolia due to nomenclatural priority. 2) Because the neotypification of the name was part of a paper focused on nomenclature, no description, circumscription, or formal synonymizations were made, leaving the correct application of the name C. latifolia unclear. This ambiguity led taxonomists and horticulturists to identify plants from different populations of SLP as C. latifolia, even though the morphological differences among populations were clear. In this study, we focus in a group of populations from the Municipality of Xilitla, SLP, that were considered to be C. latifolia since 1980s. However, when comparing the morphology between wild C. latifolia plants and the plants from Xilitla, they differ in multiple vegetative and reproductive traits. Here, we present morphological and anatomical data to demonstrate that these populations from Xilitla do not correspond to the current concept of C. latifolia or to the southern neighbors C. chamberlainii or C. fuscoviridis, but rather they belong to a new species that we describe as C. reesii sp. nov.