A systematic and biogeographic study of Trillium (Melanthiaceae)

Trillium (Melanthiaceae, Parideae) has a disjunct distribution occurring in eastern and western North America, and eastern Asia. Past studies have examined the phylogeny and historical biogeography of Melanthiaceae and Parideae, however these studies either did not fully examine these aspects within Trillium or did not employ sufficiently broad taxonomic or character sampling to clarify relationships among taxa. The first phylogenetic analysis presented in this study provides a resolved phylogeny for Trillium s.l. and Paris s.l. by using a dataset of 70 plastid coding genes and by sampling broadly from Trillium s.s., Pseudotrillium, Trillidium, Paris s.s., Daiswa, and Kinugasa. The results suggested that each of the six genera of Parideae are monophyletic and that Daiswa is sister to Paris rather than Trillium in contrast to some previous studies. The study also illustrated that omitting key taxa fundamentally affects the phylogeny topology, thus changing our understanding of taxonomic relationships. A new subgeneric classification of Trillium was presented based on the results of the analysis. In addition, the divergence time and historical biogeographical analyses estimated that diversification in Trillium lasted from the Miocene through the Pleistocene and that its origin was centered in eastern North America. The second phylogenetic analysis examined relationships within T. subgen. Sessilium with an emphasis on the T. cuneatum complex. The results of the analysis showed that T. cuneatum is paraphyletic and forms a clade including T. maculatum, T. luteum, and five other separate lineages. Two species, T. freemanii sp. nov. and T. radiatum sp. nov., were described from two of these lineages. Morphological observations of T. cuneatum s.s., T. luteum, T. maculatum, and the novel species were compared. In addition, previous morphological classifications of T. subgen. Sessilium were re-evaluated. The third phylogenetic analysis focused on the disjunct populations of T. lancifolium and closely related species, T. recurvatum. The results showed that T. lancifolium is paraphyletic, forming a clade which included a monophyletic T. recurvatum and seven highly supported lineages of T. lancifolium. Hypotheses regarding gene flow among populations within river watersheds and physiographic boundaries were discussed and the results of a seed germination experiment were presented.