Members of the cactus family are keystone species of arid and semiarid biomes in the Americas, as they provide shelter and resources to support other members of ecosystems. Extraordinary examples are the several species of flies of the genus Drosophila that lay eggs and feed in their rotting stems, which provide a model system for studying evolutionary processes. Although there is significant progress in understanding the evolution of Drosophila species, there are gaps in our knowledge about the cactus lineages hosting them. Here, we review the current knowledge about the evolution of Cactaceae, focusing on phylogenetic relationships and trends revealed by the study of DNA sequence data. During the last several decades, the availability of molecular phylogenies has considerably increased our understanding of the relationships, biogeography, and evolution of traits in the family. Remarkably, although succulent cacti have very low growth rates and long generation times, they underwent some of the fastest diversifications observed in the plant kingdom, possibly fostered by strong ecological interactions. We have a better understanding of the reproductive biology, population structure and speciation mechanisms in different clades. The recent publication of complete genomes for some species has revealed the importance of phenomena such as incomplete lineage sorting. Hybridization and polyploidization are common in the family, and have been studied using a variety of phylogenetic methods. We discuss potential future avenues for research in Cactaceae, emphasizing the need of a concerted effort among scientists in the Americas, together with the analyses of data from novel sequencing techniques.

The assembly of regional biotas and organismal responses to anthropogenic climate change both depend on the capacity of organisms to adapt to novel ecological conditions. Here we demonstrate the concept of evolutionary lag time, the time between when a climatic regime or habitat develops in a region and when it is colonized by a given clade. We analyzed the time of colonization of four clades (three plant genera and one lizard genus) into the Atacama–Sechura Desert of South America, one of Earth’s driest and oldest deserts. We reconstructed time-calibrated phylogenies for each clade and analyzed the timing of shifts in climatic distributions and biogeography and compared these estimates to independent geological estimates of the time of origin of these deserts.ChaetantheraandMalesherbia(plants) andLiolaemus(animal) invaded arid regions of the Atacama–Sechura Desert in the last 10 million years, some 20 million years after the initial onset of aridity in the region. There are also major lag times between when these clades colonized the region and when they invaded arid habitats within the region (typically 4–14 million years). Similarly, hyperarid climates developed ∼8 million years ago, but the most diverse plant clade in these habitats (Nolana) only colonized them ∼2 million years ago. Similar evolutionary lag times may occur in other organisms and habitats, but these results are important in suggesting that many lineages may require very long time scales to adapt to modern desertification and climatic change.

PREMISE OF THE STUDY: Species of the endemic Chilean cactus genus Copiapoa have cylindrical or (sub)globose stems that are solitary or form (large) clusters and typically yellow flowers. Many species are threatened with extinction. Despite being icons of the Atacama Desert and well loved by cactus enthusiasts, the evolution and diversity of Copiapoa has not yet been studied using a molecular approach.METHODS: Sequence data of three plastid DNA markers (rpl32‐trnL, trnH‐psbA, ycf1) of 39 Copiapoa taxa were analyzed using maximum likelihood and Bayesian inference approaches. Species distributions were modeled based on geo‐referenced localities and climatic data. Evolution of character states of four characters (root morphology, stem branching, stem shape, and stem diameter) as well as ancestral areas were reconstructed using a Bayesian and maximum likelihood framework, respectively.KEY RESULTS: Clades of species are revealed. Though 32 morphologically defined species can be recognized, genetic diversity between some species and infraspecific taxa is too low to delimit their boundaries using plastid DNA markers. Recovered relationships are often supported by morphological and biogeographical patterns. The origin of Copiapoa likely lies between southern Peru and the extreme north of Chile. The Copiapó Valley limited colonization between two biogeographical areas.CONCLUSIONS: Copiapoa is here defined to include 32 species and five heterotypic subspecies. Thirty species are classified into four sections and two subsections, while two species remain unplaced. A better understanding of evolution and diversity of Copiapoa will allow allocating conservation resources to the most threatened lineages and focusing conservation action on real biodiversity.