Reticulate evolution in the parasitic genus Cuscuta (Convolvulaceae):: over and over again

The frequency and relative importance of hybridization in plants has been an area of intense debate. Although this evolutionary phenomenon has received considerable attention from plant biologists, there are no well-supported cases of reticulate evolution involving parasitic plants, to date. Recent molecular phylogenetic analyses revealed that the subgenus Grammica, the largest and most diverse group of the stern-parasitic genus Cuscuta (dodder), consists of 15 major clades. We describe here five cases of strongly supported discordance between phylogenies derived from plastid and nuclear data, and interpret them as results of five independent hybridization events. Three of these cases could represent relatively recent reticulations, as each of them involves more closely related species, always confined within the same major clade as their putative parental species, and are currently sympatric or parapatric with them. The two remaining cases involve species whose potential progenitors are derived from different major groups of Grammica, and which are allopatric in their present distribution. A series of statistical tests was conducted to assess and further explore the significance of this phylogenetic incongruence. Alternative explanations for discordant gene topologies are explored. Cuscuta liliputana sp. nov., a new Mexican species of hybrid origin is described.