Hemiparasitic plants are broadly classified as generalists with respect to their host specificity. However, a generalist species may be associated with different host communities throughout its geographic range, possibly leading to locally adapted host preferences that may ultimately drive speciation through ecological isolation. Because haustorial connections to hosts can be difficult to identify in natural populations, little is known about the evolution of host range in hemiparasitic plants and the role that host-switching plays in their diversification. Pedicularis (Orobanchaceae) is a genus of facultative root hemiparasites that parasitizes a taxonomically diverse array of hosts. Here I examine the variation in potential host communities of Pedicularis densiflora and Pedicularis aurantiaca, a pair of putative sister species distributed around the Central Valley of California. Potential host use was determined by compiling mentions of co-occurring plant species from herbarium labels. Preliminary results indicate that P. densiflora and P. aurantiaca pararisitize different hosts, and that host preference within each species varies by location. Genetic analysis of P. densiflora and P. aurantiaca populations across their geographic range will be conducted in order to investigate how host preference has affected genetic variation between and within each species. This research will shed light on the evolution of host specificity and the role it plays in the diversification of parasitic plants.