Hybridization in Hydrophiles: Natural Interspecific Hybrids in Najas (Hydrocharitaceae)

Abstract Pollination by water (hydrophily) is a highly specialized mechanism that occurs rarely among aquatic angiosperms, which mainly retain the reproductive systems reminiscent of their terrestrial ancestors. Hydrophily is abiotic and typically associated with unisexual flowers, factors that predictably would promote xenogamy and outcrossing. Yet, there have been few reports of hybridization involving waterpollinated plants (hydrophiles), with no firm evidence of natural interspecific hybridization. The genus Najas comprises about 40 species of submersed aquatic plants, all characterized by subsurface hydrophily. Hybridization in this genus has been suspected, but verified previously only among infraspecific taxa. In this study we document the first instance of interspecific hybridization in Najas using genetic evidence from three populations that were identifiable as N. guadalupensis but yielded polymorphic DNA sequence profiles. To facilitate our analysis we first conducted a phylogenetic survey of N...