A Systematic Study of Trillium subgenus Delostylis

This study focused on the systematics of Trillium subg. Delostylis, an enigmatic group endemic to the southeastern United States. Phylogenetic analysis of DNA sequence data was used to examine the circumscription and phylogenetic placement of Delostylis. The results of the phylogenetic analysis of data from the ITS, matK, and psbA-trnH sequence data suggested that the circumscription of Delostylis be narrowed to consist of T. persistens, T. catesbaei, and T. pusillum sensu lato. A revised Delostylis was characterized by the presence of a style with three slender stigmatic branches in those plants whose flowers are either white-fading-to-pink or pink. Results of the phylogenetic analysis showed Delostylis to be one of four innermost clades in Trillium (the other three being T. ovatum [bootstrap 100%; posterior probability 1.0], T. subg. Phyllantherum [100%; 1.0], and sister taxa T. grandiflorum and T. nivale [86%; 1.0]). Phylogenetic analyses of DNA sequence data as well as statistical analysis of quantitative morphological characters in conjunction with geographic distribution, physiography, and habitat preference were used to address the questions of species-level taxonomy. Molecular evidence suggested that the narrowly endemic Trillium persistens was monophyletic, but T. catesbaei was not. The remaining members of Delostylis form the Pusillum Complex which was found to be composed of ten species (four of them new) in three groups rather than a single species with one or more varieties. The Pusillum Cluster included T. pusillum, T. texanum, T. georgianum (sp. nov.), and T. telmacola (sp. nov.); the Ozarkanum Cluster included T. ozarkanum and T. alabamicum (sp. nov.); and the Virginianum Cluster included T. virginianum, T. monticola (stat. nov.), T. carolinianum (sp. nov.), and T. palustris (sp. nov.). Five of the 10 species that are included within the Pusillum Complex are known from five counties or less (T. telmacola, T. carolinianum, T. georgianum, T. monticola and T. pusillum) and should certainly be considered for protection.