The genus Ceratozamia contains more than 20 species distributed in eastern and southern Mexico, with extensions into Central America. Morphology, anatomy, and molecular (ITS) data allow resolution of some aspects of species relationships, provide correlations with ecology, and suggest phytogeographic hypotheses. Some species complexes, such as those centered around C. norstogii and C. miqueliana, are restricted to southernwest Mexico, in what are regarded as Pleistocene floristic refugia. The low level of divergence of ITS sequences among taxa to the north of the Trans–Mexican Neovolcanic mountain range suggests a pattern of recent, and perhaps rapid, speciation.

Species relationships and phytogeography of Ceratozamia, an endangered neotropical cycad genus, based on morphology, leaflet histology, DNA sequencing and ecological data, are analysed and discussed. Seven species complexes are assigned within the genus. A centre of origin in south-eastern Mexico, with recent speciation and immigration patterns, is proposed.

Explorations in central Veracruz on the Transvolcanic Mexican Belt and regions explored by 19th century botanists we found various populations of Ceratozamia whose taxonomic status is not yet completely clear. Especially two populations of C. mexicana with distinct morphology; one population at El Esquilón considered as C. mexicana by Chamberlain and other authors, and another population at El Mirador that Stevenson found a voucher at the herbarium in Paris with oblanceolate leaflets collected by Ghiesbrecht and designated it as Brongniart's holotype. The plants from El Mirador are comparable to the holotype of C. mexicana, but those at El Esquilón do not. Stevenson later also found a voucher at Kew by Thiselton-Dyer as C. mexicana var. tenuis from Mexico with linear-lanceolate leaflets that is similar to the plants at the El Esquilón population. An analysis of 11 leaflet anatomical characters gave a significant discriminant pattern (Wilk's lambda 0.00015 P < 0.01). The squared Mahalanobis distances were also significant (P < 0.05) and the first canonic variable showed that 93.4 % of the variation was due to the anatomical characters. A new nomenclatural combination is proposed and Thiselton-Dyer's voucher assigned as the lectotype of Ceratozamia tenuis. Epitypes were also designated for the two species in support of the anatomical analysis as well as a description for both species given.

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