Andean connections for amphitropic desert disjuncts in Verbenaceae: yes, no, or maybe?

Abstract

Verbenaceae originated and initially diversified in South America in wet forest habitats. They have diversified extensively in arid habitats in both South and North America. This study aims to understand the origin of the North American desert species of Verbenaceae. A phylogenetic approach is used to examine four genera (Aloysia, Citharexylum, Glandularia, Verbena) in three distinct clades with representatives in North American deserts and disjunct South and North American distributions. Phylogenetic analyses were conducted using maximum likelihood and Bayesian approaches. Analyses included both plastid and nuclear DNA regions. North American desert species of Aloysia and Glandularia were likely derived from ancestors in arid temperate South America, perhaps by long distance dispersal. The pattern for Verbena was less clear, with evidence from plastid DNA implicating Andean species as sister to the North American clade, while nuclear data suggest that the Andean species nest with southern South America species. A previously unrecognized clade of Andean Verbeneae was discovered, raising the possibility of an Andean origin of Verbena or Verbena and Glandularia. Citharexylum does not occur in the desert regions of temperate South America, and North American desert species represent multiple, independent origins from mesic habitat ancestors in Mesoamerica. North American arid-zone Verbenaceae are derived from South and Central American ancestors via multiple avenues, including long distance, amphitropical dispersal, Andean migration corridors, and in situ evolution of desert-adapted species.