The genus Zamia is revised for Mega-Mexico, with 22 species recognized and described. The study presents a taxonomic clarification for the genus in Mesoamerica, a contribution that provides the foundation for a future monograph for Zamia in the Neotropics. The largest proportion of species richness and endemism for the genus is concentrated in southeastern Mexico, among the states of Chiapas, Oaxaca, Tabasco, and Veracruz, an area that is considered highly diverse in floristic terms. Distribution maps and a key to species are also provided, as well as complete descriptions of the specimens examined, including information on nomenclatural types, habitats, synonymies, and etymologies. A lectotype is designated for Zamia loddigesii, and neotypes for Z. galeottii, Z. leiboldii var. angustifolia, and Z. variegata. Zamia spartea is illustrated for the first time, and chromosome numbers for Z. herrerae are reported and illustrated. Finally, scanning electron micrographs of leaflet trichome character states are presented, along with a discussion of their systematic implications within the group.

Ceratozamia is a genus of cycads occurring in eastern Mexico and Central America. In this study, we describe a new species from the Pacific region of Mexico in Guerrero state. This locality represents the most northwestern Mexico distribution for the genus. We focus the comparison of this species with the most geographically proximate and phenotypically relevant lineages for this taxon. We followed an integrative taxonomy approach to evaluate the classification of these species, including geographic location, morphology, DNA barcoding and phenology as primary sources of systematic data. Within the morphological dataset, reproductive structures are described in detail and new characters are proposed for microsporophylls. The comparative morphology of these structures facilitated the elucidation of differences in forms and species for identification. The two chosen DNA barcoding markers – namely, the chloroplast genome coding region matK and the nuclear ribosomal internal transcribed spacer (ITS) region – had low divergence, allowing only 61% of species identification, suggesting slow molecular evolutionary rates. Besides employing these three basic sources of evidence, we introduced phenology as additional information for species circumscription. In addition, this work includes a brief review of the genus at the species-level. This is therefore the most recent review for Ceratozamia across its full geographic range (latitudinal and elevational). Overall, this work further contributes to a comprehensive framework for systematic studies in Mexican cycads.

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Taxonomía y sistemática Conceptos taxonómicos, fenología y epifitismo: el caso de Ceratozamia tenuis (Zamiaceae) Taxonomic concepts, phenology and epiphytism: the case of Ceratozamia tenuis (Zamiaceae)

The genetic diversity and structure of four populations of the cycad Zamia loddigesii were studied throughout its range in Mexico. Allozyme electrophoresis of 15 loci was conducted. The mean number of alleles per locus was 1.80 ± 0.09, the percentage of polymorphic loci was 66.6 ± 5.4, and the expected heterozygosity was 0.266 ± 0.02. The results indicated that the genetic diversity was relatively higher, with respect to tropical tree species and other cycads. The genetic variation explained by differences among populations was 18%. On average, gene flow between paired populations was similar ( Nm = 1.6) to other tropical forest trees and cycad species. Our results indicated that the geographical isolation among populations of Z. loddigesii generated allele loss, as well as a clinal variation in the frequencies of two loci ( MDH and MNR2 ), in relation to the latitudinal distribution of populations. The populations have become fragmented due to increasingly higher pressure of habitat conversion and disturbance. The importance of the establishment of sanctuaries and protected areas and a reduction in deforestation is highlighted in this research as a way of preserving the high genetic diversity of this and other endemic species. AA. 1994. Population genetic structure of Cecropia obtusifolia, a tropical pioneer tree species. Evolution 48: 437-453. Alvarez-Buylla ER, García-Barrios R, Lara-Moreno C, Martínez-Ramos M. 1996. Demographic and genetic models in conservation biology. Applications and perspectives for tropical rain forest tree species.

A new species, from the montane region of Los Tuxtlas (state of Veracruz, Mexico), Ceratozamia subroseophylla, is proposed in accordance with the integrative taxonomy framework and through application of the taxonomic circle rationale. Our identification of this new species is the result of a thorough re-evaluation of four formerly described Ceratozamia species, namely: (1) C. miqueliana, with which it overlaps geographically; (2) C. mexicana; (3) C. robusta, which has also been previously seen as morphologically similar to C. miqueliana; and (4) C. brevifrons, which was at the center of a controversy concerning the morphological and geographic limits when compared to C. mexicana. Even though there are morphometric affinities of C. subroseophylla with this set of species, there are apomorphies in qualitative morphological characters and diagnostic nucleotidic variants established through character-based DNA barcoding to allow the recognition of this new species. The implications that our integrative taxonomy-based assessment of systematic diversity in Ceratozamia species from Veracruz have for evaluating the overall taxonomic status of the genus are discussed.

We have estimated levels of genetic diversity and partitioning in the Mexican endemic cycad species Dioon sonorense, Dioon tomasellii, and Dioon holmgrenii, whose populations are exclusively distributed along the Pacific seaboard. For the three species, the patterns of variation at 19 allozyme loci in a total of 11 populations were evaluated. The average number of alleles per locus was in the range 2.05-1.68, corresponding to the northernmost population of D. sonorense (Mazatán), and the southernmost population of Dioon holmgrenii (Loxicha), respectively. In turn, the percentage of polymorphic loci peaked (94.73) in the El Higueral and Altamirano populations of Dioon tomasellii, and was estimated to be lowest (57.89) in the Loxicha population of D. holmgrenii. The mean expected heterozygosis varied markedly between taxa, with relatively high indices for D. sonorense and D. tomasellii (HE = 0.314 and 0.295, respectively) and substantially lower values for D. holmgrenii (HE = 0.170). Comparison of the inferred genetic structure based on F-statistics for the three species also indicated differences along the north-south Pacific seaboard axis. For D. sonorense and D. tomasellii, local inbreeding (FIS) was zero but global inbreeding (FIT) values were positive and significantly different from zero (0.130 and 0.116, respectively). By contrast, values of both FIT and FIS were negative and significantly different from zero (-0.116 and -0.201, respectively) for D. holmgrenii. The genetic differentiation between populations (FST) had positive values in all taxa and corresponded with their geographic location along the north-south axis: according to this statistic, D. sonorense was the most differentiated species (FST = 0.151), D. tomasellii had intermediate values (FST = 0.145), and D. holmgrenii was the less differentiated taxon (FST = 0.069). Finally, a phenogram representing Nei's genetic distances among populations displayed three major groups, each one corresponding to each of the studied species. Within D. tomasellii (of intermediate geographic distribution), a further division into two clusters corresponded precisely to the pair of populations that are geographically divided by the Trans Mexican Neovolcanic Mountains.

Observaciones generales. El orden Cycadales, división Cycadophyta, es un taxón perteneciente al grupo informal de las gimnospermas dentro de la superdivisión Spermatophyta -reino Plantae, subreino Tracheobionta-. Comprende 10 géneros modernos: