These comprehensive analyses of systematic relationships within Trilliaceae focused on the relationships within Paris sensu lato (i.e., Paris, Daiswa, and Kinugasa); between species of Trillium; and between Paris sensu lato and Trillium. Seventy species were selected for cladistic analyses and scored for 110 morphological characters; matK and ITS molecular characters were obtained from GenBank for a subset of 26 taxa. Based on the preliminary results, Trillium rivale was used as a functional outgroup. For the subset of 26 species, analysis of the combined ITS and matK sequence data produced six shortest trees; the morphological data, 13 shortest trees; and the combined morphological and molecular data sets, three trees. Analyses of the full morphological data set of 70 species produced 76 shortest trees. Trillium rivale was distinct from both Paris and Trillium and should be placed in its own genus, for which the name Pseudotrillium is proposed. Trillium govanianum was more closely related to Paris than to Trillium but should be retained as a monotypic genus, Trillidium. Trillium and Paris were monophyletic based on molecular as well as morphological evidence. The cladistic analyses strongly support the separation of Paris sensu lato into Daiswa, Kinugasa, and Paris. The monophyly of Trillium after removal of Pseudotrillium and Trillidium was supported in all but the large morphological analysis; subgenus Phyllantherum was monophyletic in all cases, but subgenus Trillium was not monophyletic.
Communicating Editor: Jeff H. Rettig