Molecular systematics of Trilliaceae I.: Phylogenetic analyses of Trillium using matK gene sequences

Comparative DNA sequencing of the chloroplast gene matK was conducted using 41 Trillium taxa and two outgroup taxa (Veratrum maackii and Helonias bullata). A total of 1608 base pairs were analyzed and compared., and then there were 61 variable (36 informative) sites among Trillium species. Fifteen insertion/deletion events (indels) of six or fifteen base pairs were also detected. Phylogenetic analyses of the sequence data revealed that the subgenus Phyllantherum (sessile-flowered species) forms a distinct monophyletic group, whereas the subgenus Trillium (pedicellate-flowered species) does not form a monophyletic group, and is composed of three distinct groups and three basally located species in the tree: (1) the Erectum group, (2) the Grandiflorum group, and (3) the Pusillum group and (4) the three species, including T. govanianum, T. undulatum, and T. rivale. T. rivale appears to be the most basally diverged and a very specialized taxon among the ingroup members. Our matK data indicated that the closest relative of the subgenus Phyllantherum is the Grandiflorum group. The results are concordant with the results of the RFLP analysis of cpDNA and also more or less with those of the cladistic analysis of morphological characters.