• Background and Aims Genetic structure and variability were examined in the only three extant populations of the narrow‐endemic tree Antirhea aromatica (Rubiaceae, Guettardeae), an endangered species of the tropical forest of eastern Mexico. Patterns of genetic diversity within and among populations for adult plants and seedlings were obtained. • Methods Allozyme electrophoresis of 15 loci was conducted and the data analysed with statistical approximation for obtaining genetic diversity, structure and gene flow. • Key Results The mean expected heterozygosity (H_e) in the adult and seedling populations was 0·18 ± 0·08 and 0·20 ± 0·09, respectively. The genetic variation explained by differences among populations was 51 and 35 %, for adult and seedling populations, respectively. On average, gene flow between paired adult populations was low (Nm = 0·26 ± 0·09), compared with other trees from the tropical forest. • Conclusions The results indicated that the populations evaluated have high genetic variability, compared with other endemic and geographically narrowly distributed plant species, in areas with high levels of environmental heterogeneity (e.g. tropical forests). The conservation implications of the results are discussed, and in this regard it is proposed that A. aromatica should be considered as an indicator species with economic potential. It is suggested that sustainable management practices should be implemented and that the areas where the species is distributed should be declared a natural reserve to ensure the species conservation.

• Background and Aims The monoecious, bird-pollinated epiphytic Tillandsia achyrostachys E. Morr. ex Baker var. achyrostachys is an endemic bromeliad of the tropical dry forests of Mexico with clonal growth. In the Sierra de Huautla Natural Reserve this species shows a host preference for Bursera copallifera (Sessé & Moc ex. DC) Bullock. As a result of deforestation in the study area, B. copallifera has become a rare tree species in the remaining forest patches. This human-induced disturbance has directly affected the population densities of T. achyrostachys. In this study the genetic consequences of habitat fragmentation were assessed by comparing the genetic diversity, gene flow and genetic differentiation in six populations of T. achyrostachys in the Sierra de Huautla Natural Reserve, Mexico. • Methods Allozyme electrophoresis of sixteen loci (eleven polymorphic and five monomorphic) were used. The data were analysed with standard statistical approximations for obtaining diversity, genetic structure and gene flow. • Key Results Genetic diversity and allelic richness were: H_E = 0·21 ± 0·02, A = 1·86 ± 0·08, respectively. F-statistics revealed a deficiency of heterozygous plants in all populations (F_it = 0·65 ± 0·02 and F_is = 0·43 ± 0·06). Significant genetic differentiation between populations was detected (F_st = 0·39 ± 0·07). Average gene flow between pairs of populations was relatively low and had high variation (Nm = 0·46 ± 0·21), which denotes a pattern of isolation by distance. The genetic structure of populations of T. achyrostachys suggests that habitat fragmentation has reduced allelic richness and genetic diversity, and increased significant genetic differentiation (by approx. 40 %) between populations. • Conclusions The F-statistic values (>0) and the level of gene flow found suggest that habitat fragmentation has broken up the former population structure. In this context, it is proposed that the host trees of T. achyrostachys should be considered as a conservation priority, since they represent the limiting factor to bromeliad population growth and connectivity.

Dentro de los grupos actuales de espermatofitas, plantas con semilla, las cícadas cuentan con el registrofósil más antiguo. A pesar de ello, su estatus como “fósiles vivientes” ha sido puesto en entredicho recientemente conbase en resultados de estudios filogenéticos moleculares. El grupo presenta apomorfías morfológicas vegetativas yposiblemente también reproductivas, siendo Cycas el género más divergente. Junto con Australia y Sudáfrica, Méxicoes uno de los 3 centros de diversidad del orden Cycadales, con 54 especies pertenecientes a 3 de los géneros queconstituyen la familia Zamiaceae: Ceratozamia, Dioon y Zamia. En este sentido, México es la región más diversay con el mayor número de endemismos (88.9%) de la familia Zamiaceae en el Neotrópico. En general, el estado deconservación de los 3 géneros es crítico, debido a lo cual, todas las especies de cícadas mexicanas se encuentran bajoalguna categoría de riesgo, de acuerdo con la Nom-059-Semarnat-2010. Finalmente, consideramos que el conocimientogenerado hasta el momento sobre las cícadas en nuestro país, en términos de sistemática, biología evolutiva yconservación, nos permitirá esclarecer diferentes escenarios evolutivos, principalmente aquellos relacionados con losprocesos y los patrones que han determinado su diversidad actual.