| Trillium (Melanthiaceae: Liliales) is a highly diverse genus of monocots characteristic of forest understories in eastern and western North America and eastern Asia. The Trillium erectum complex includes three widespread species from eastern North America and four species narrowly endemic to the southern, Appalachians; relationships within this complex remain poorly resolved, and recently debate has arisen as to its circumscription. Here I use DNA sequences from the plastid and nuclear genomes to evaluate relationships among all pedicellate Trillium of North America and clarify the identity of the Trillium erectum complex. Maximum-parsimony and maximum-likelihood analyses strongly support a monophyletic complex including T. simile, placing it sister to the Asian pedicellate trilliums and revealing surprisingly little genetic divergence among members of the complex. A penalized-likelihood analysis reveals that Trillium arose 7-10 Mya, that the Trillium erectum complex and its Asian sister-group diverged 1.6-2.4 Mya, and that divergence among species within the complex occurred over the past 600,000 to 900,000 years. The disjunction between eastern Asia and eastern North America implied by this study appears to be the youngest documented to date, and apparently involved dispersal-vicariance from eastern North America to eastern Asia via Beringia.; Relationships within the Trillium erectum complex were explored using the rapidly evolving rbcL-accD spacer of the plastid genome. Extremely little DNA sequence divergence was found among species, resolving an early split, into two lineages but with little variation within each. The cernuum lineage comprises Trillium cernuum and Midwestern populations of T. flexipes. The erectum lineage comprises the remaining species (including Appalachian and eastern popula tions of T. flexipes), in which none appear to be purely monophyletic, but in which first several populations of T. rugelii and then T. vaseyi diverge from other taxa. Extensive chloroplast capture appears to have occurred along the Eastern seaboard and in northern Alabama/Georgia. A molecular clock estimates that the cernuum and erectum lineages diverged starting 900,000 years ago, and that species within these lineages began diverging 90,000 and 280,000 years ago, respectively. All species---including four taxa narrowly endemic to the southern Appalachians---are recently divergent from each other. |
