A Nuclear rDNA Phylogeny of Smilax (Smilacaceae)

Abstract

Smilacaceae are a taxonomically confused, cosmopolitan family of Liliales characterized by climbing habit, reticulate leaf venation, paired petiolar tendrils, unisexual flowers, and superior ovaries. Deviations from this generalized morphology have led to the division of Smilacaceae into at least seven different genera and five sections within the large genus Smilax. In particular, taxa with connate tepals (Heterosmilax), more than six stamens (Pleiosmilax, Oligosmilax), or herbaceous habit (Hemexia) have been variously classified. Using DNA sequences of 96 taxa from the nuclear rDNA ITS gene region, parsimony analyses provide moderate resolution, but generally poor bootstrap support for phylogenetic relationships in the family. Rhipogonum and Lapageria are closely related to Smilax, but may be better classified in separate families. Within Smilax few of the sections are monophyletic, but three major lineages are evident. The first is a primarily Old World clade that contains species of Heterosmilax, the erect, woody species of Smilax from Asia, and the herbaceous Smilax species. Within this clade there is evidence that the S. herbacea complex represents a single eastward dispersal from Asia to North America. A primarily New World clade (or paraphyletic grade in some trees) is also present in the ITS cladogram. From within this group there is evidence of a single westward dispersal from North America to Asia. The third lineage is represented by S. aspera, which is the sole member of Smilax section Smilax, and is sister to the entire genus. Its position in the cladogram is intriguing and may help to shed light on the family's greater evolutionary and biogeographic history.