In the carnivorous plant family Lentibulariaceae, the bladderwort lineage (Utricularia and Genlisea) is substantially more species-rich and morphologically divergent than its sister lineage, the butterworts (Pinguicula). Bladderworts have a relaxed body plan that has permitted the evolution of terrestrial, epiphytic, and aquatic forms that trap prey in intricately-designed suction bladders. In contrast, the flypaper-trapping butterworts maintain vegetative structures typical of angiosperms. We found that bladderwort genomes evolve significantly faster across seven loci (the trnL intron, the second trnL exon, the trnL-F intergenic spacer, the rps16 intron, rbcL, coxI, and 5.8S rDNA) representing all three genomic compartments. Generation time differences did not show a significant association. We relate these findings to the contested speciation rate hypothesis, which postulates a relationship between increased nucleotide substitution and increased cladogenesis. Body-plan relaxation would lower selection pressure as individuals with novel phenotypes establish founder populations and diverge. In agreement with known prey specificities and interbreeding barriers among bladderworts, the strong correlation between bladder variety and phylogeny (estimated from 69 Lentibulariaceae and 10 outgroups based on trnL-F and rps16 intron sequences) suggests that diversifying (disruptive) selection on trap form has further driven rate increases. Additionally, bladderwort features such as rootlessness, asymmetrical phyllotaxy, and leaf-shoot indistinction resemble phenotypes of known auxin transport mutants, suggesting that one or few genes of large effect could underlie bladderwort developmental release (see abstract by Albert and Jobson, Botany2001). Finally, we argue that molecular and speciation rate increases may amplify each other as greater genetic variation feeds into the system, resulting in "explosive" radiation (i.e., punctuational evolution).

Key words: Lentibulariaceae, molecular evolution, Pinguicula, speciation rate, Utricularia