XVI International Botanical Congess

The taxonomic history of the Cactaceae is replete with examples ofmisinterpretation of morphological characters and overdescription atgeneric and species levels. Much of the confusion is derived from effects of evolutionary parallelisms, phenotypic plasticity, and narrowgenus/species concepts. Using representatives from all major groups within the family, molecular studies have provided data to help resolve several key issues in cactus systematics. Most significantly, these new data assist with a phylogenetic interpretation of the cacti. The following primary conclusions are supported by molecular data: recognition of Maihuenia as a distinct group at the subfamilial level, determination of natural generic groups within Subfam. Opuntioideae, in subfamily Cactoideae, two distinct clades are supported for the columnar lineages, the two epiphytic lineages were found to have independent origins. Intergeneric and tribal delimitation studies continue, particularly for the placement of anomalous genera, as well as phylogenetic studies at the species level.