ABSTRACT Cactaceae species are karyotypically well-known with x = 11 and chromosome number variation due mainly to polyploidization. However, both assumptions are based on descriptive observations without taking an evolutionary framework of Cactaceae into account. Aiming to confirm these hypotheses in an evolutionary context, we obtained chromosome numbers for 20 species of Cactoideae, performed an extensive review of chromosome number for the family, and analyzed these data using a phylogenetic approach. The karyotypes presented here were characterized by CMA/DAPI banding, and for six species 5S and 45S rDNA sites were located. Our data, along with a survey of the literature, reinforce the long-standing hypothesis of a x = 11 as the base chromosome number for Cactaceae. They also reinforce the relevance of polyploidy in karyotype evolution of cacti, although polyploidy was important just after the diversification of subfamilies Maihuenioideae and Pereskioideae. Despite the homogeneous chromosome complements observed among cacti, chromosome banding and FISH techniques revealed informative characteristics, allowing the identification of chromosome synapomorphies, such as proximal CMA+ bands in Melocactus and proximal 5S rDNA in Pilosocereus, indicating the taxonomic potential of chromosome characterization in cacti.

Although many phylogeographic studies have been conducted to analyze the genetic and phylogeographic structure of Mexican species, such studies are nearly absent for plants of dry seasonal forest, precincts with high level of endemism. To better understand this areas, we undertook a phylogeographic study and dating were carried out on the Caesalpinia hintonii complex distributed in the Río Balsas Depression and Tehuacán-Cuicatlán Valley. The phylogeographic structure was determined analyzing sequences from 4 plastid regions (trnL, trnL-F, psbA-trnH and accD-psaI) in all populations. A nonparametric rate smoothing (NPRS) method was employed to estimate the time of origin of the species complex. Haplotypic (0.64-1) and the nucleotide differences (3.8-11.52) were high in all species. The morphologically indistinct C. oyamae populations are genetically structured and showed 3 haplogroups where gene flow is low; considered them here as cryptic entities. The C. hintonii populations are genetically close-knit, even though they are morphologically distinct. The populations of C. macvaughii exhibit 2 divergent lineages with gene flow (Nm=1.41). Divergence events in 2 lineages between east and west from Rio Balsas Depression can be explained by geologic events. Our results showed that the C. hintonii complex is under diversification and in some cases morphostatic radiation.

A pesar del crecido número de estudios que se ha realizado para explorar la estructura genética y filogeográfica en especies mexicanas, hay carencia de estudios para especies de selva baja, zonas con alto grado de endemismo. Para un mejor entendimiento de dichas áreas se realizó un estudio filogeográfico y el fechamiento de las especies del complejo Caesalpinia hintonii distribuido en la depresión del río Balsas y el valle de Tehuacán-Cuicatlán. Se determinó la estructura filogeográfica del complejo analizando las secuencias de 4 regiones de plastidio (intrón trnL, espaciador trnL-F, espaciador psbA-trnH y espaciador accD-psaI) en todas las poblaciones disponibles. Se estimó la fecha del origen del complejo mediante un método no paramétrico (NPRS). Las diversidades haplotídicas (0.64-1) y las diferencias nucleotídicas (3.8-11.52) en todas las especies fueron altas respecto a valores registrados para otras plantas. Las poblaciones de C. oyamae, morfológicamente indistintas están genéticamente estructuradas y presentan 3 haplogrupos donde el flujo génico entre ellos es bajo y se consideraron entidades crípticas. Las poblaciones de C. hintonii son un grupo genéticamente homogéneo a pesar de ser morfológicamente distintas. Las poblaciones de C. macvaughii forman 2 linajes divergentes entre los que existe flujo génico (Nm=1.41). Los eventos de divergencia en 2 grandes linajes al este y oeste del río Balsas pueden explicarse por eventos geológicos. Los resultados indican que el complejo se encuentra bajo divergencia y en algunos casos radiación morfostática.