XVI International Botanical Congess

Parasitism has evolved many times in angiosperms, but only Scrophulariaceae (including Orobanchaceae) has members representing the full range of parasitic ability from facultative hemiparasites to nonphotosynthetic holoparasites. Phylogenetic analysis of multiple plastid genes gives strong evidence for the monophyly of parasitic Scrophulariaceae and Orobanchaceae, and a detailed hypothesis for the origin and evolution of parasitism in this group. All these parasites plus Lindenbergia (nonparasitic sister to the parasite clade) may be classified in an expanded Orobanchaceae. One origin of parasitism is strongly implied, but holoparasitism has evolved at least 5 times in this group. Plastid gene and genome evolution is remarkably diverse, including rapid structural evolution and large shifts in substitution rates, and retention or modification of genes for alternative function in nonphotosynthetic plants.