High proportion of cactus species threatened with extinction.

A high proportion of plant species is predicted to be threatened with extinction in the near future. However, the threat status of only a small number has been evaluated compared with key animal groups, rendering the magnitude and nature of the risks plants face unclear. Here we report the results of a global species assessment for the largest plant taxon evaluated to date under the International Union for Conservation of Nature (IUCN) Red List Categories and Criteria, the iconic Cactaceae (cacti). We show that cacti are among the most threatened taxonomic groups assessed to date, with 31% of the 1,478 evaluated species threatened, demonstrating the high anthropogenic pressures on biodiversity in arid lands. The distribution of threatened species and the predominant threatening processes and drivers are different to those described for other taxa. The most significant threat processes comprise land conversion to agriculture and aquaculture, collection as biological resources, and residential and commercial development. The dominant drivers of extinction risk are the unscrupulous collection of live plants and seeds for horticultural trade and private ornamental collections, smallholder livestock ranching and smallholder annual agriculture. Our findings demonstrate that global species assessments are readily achievable for major groups of plants with relatively moderate resources, and highlight different conservation priorities and actions to those derived from species assessments of key animal groups.

Interglacial microrefugia and diversification of a cactus species complex: phylogeography and palaeodistributional reconstructions for Pilosocereus aurisetus and allies.

The role of Pleistocene climate changes in promoting evolutionary diversification in global biota is well documented, but the great majority of data regarding this subject come from North America and Europe, which were greatly affected by glaciation. The effects of Pleistocene changes on cold- and/or dry-adapted species in tropical areas where glaciers were not present remain sparsely investigated. Many such species are restricted to small areas surrounded by unfavourable habitats, which may represent potential interglacial microrefugia. Here, we analysed the phylogeographic structure and diversification history of seven cactus species in the Pilosocereus aurisetus complex that are restricted to rocky areas with high diversity and endemism within the Neotropical savannas of eastern South America. We combined palaeodistributional estimates with standard phylogeographic approaches based on two chloroplast DNA regions (trnT-trnL and trnS-trnG), exon 1 of the nuclear gene PhyC and 10 nuclear microsatellite loci. Our analyses revealed a phylogeographic history marked by multiple levels of distributional fragmentation, isolation leading to allopatric differentiation and secondary contact among divergent lineages within the complex. Diversification and demographic events appear to have been affected by the Quaternary climatic cycles as a result of isolation in multiple patches of xerophytic vegetation. These small patches presently harbouring P. aurisetus populations seem to operate as microrefugia, both at present and during Pleistocene interglacial periods; the role of such microrefugia should be explored and analysed in greater detail.

Cross-species amplification of microsatellites reveals incongruence in the molecular variation and taxonomic limits of the Pilosocereus aurisetus group (Cactaceae).

The Pilosocereus aurisetus group contains eight cactus species restricted to xeric habitats in eastern and central Brazil that have an archipelago-like distribution. In this study, 5-11 microsatellite markers previously designed for Pilosocereus machrisii were evaluated for cross-amplification and polymorphisms in ten populations from six species of the P. aurisetus group. The genotypic information was subsequently used to investigate the genetic relationships between the individuals, populations, and species analyzed. Only the Pmac101 locus failed to amplify in all of the six analyzed species, resulting in an 88 % success rate. The number of alleles per polymorphic locus ranged from 2 to 12, and the most successfully amplified loci showed at least one population with a larger number of alleles than were reported in the source species. The population relationships revealed clear genetic clustering in a neighbor-joining tree that was partially incongruent with the taxonomic limits between the P. aurisetus and P. machrisii species, a fact which parallels the problematic taxonomy of the P. aurisetus group. A Bayesian clustering analysis of the individual genotypes confirmed the observed taxonomic incongruence. These microsatellite markers provide a valuable resource for facilitating large-scale genetic studies on population structures, systematics and evolutionary history in this group.