Gypsum exposures occur in an island-like distribution throughout the Chihuahuan Desert region of southwestern North America.  For gypsophiles, migration between gypsum exposures can be very rare because of this island-like distribution.  This lack of gene flow results in isolation and therefore genetic differentiation among gypsophile populations.  Anulocaulis (Nyctaginaceae) is a genus of five species, all native to northern Mexico and the western USA and commonly referred to as “ringstems.”  Anulocaulis includes a clade of two gypsophile species (A. leiosolenus and A. reflexus) that have long floral tubes and are hawkmoth-pollinated, but whose fruits are likely gravity-dispersed.  Because of the island-like distribution of gypsum, gypsophilic Anulocaulis populations are isolated from each other, which promotes divergence. However, hawkmoths can carry pollen long distances, and thus, hawkmoth pollination may help to maintain genetic connectivity between these disparate populations.  This push-pull between divergence and genetic connectivity may be responsible for the confusing patterns of morphological variation that exist in gypsophilic Anulocaulis, with some groups of populations having been called different species while others having been called different varieties within the same species.  The taxonomy of this group has been established through morphological study; however, the taxonomy has only been studied using DNA sequence data from a few genes, giving inconclusive results.  We are sequencing DNA of hundreds of genes from populations throughout the range of gypsophile Anulocaulis to test the traditional species and variety boundaries.  We hypothesize that although they look similar, A. leiosolenus var. leiosolenus populations in Nevada and Arizona are genetically quite different than other populations of this variety because they are so geographically separated and may represent a cryptic species.  We also hypothesize that given the strong morphological differences between A. leiosolenus var. gypsogenus and other A. leiosolenus varieties, our molecular data will show that it should be recognized as a separate species.