Research interests:

Introduction
    In my graduate research I study the aquatic and wetland plant family Menyanthaceae (Bercht. & J.Presl), in particular the relationships among species and the evolution of floral reproductive systems. Species of Menyanthaceae are found worldwide, and are divided taxonomically among six genera. The reproductive systems of Menyanthaceae species are of particular interest, because the family contains both hermaphroditic and dioecious species, and many hermaphroditic species are also heterostylous. In addition, species in the genus Nymphoides Ség., while rooted in the substrate, have a floating-leaf habit reminiscent of many other, unrelated aquatic plant lineages.

Taxonomy
    The six genera of Menyanthaceae are Liparophyllum Hook.f., Menyanthes L., Nephrophyllidium Gilg (= Fauria Franch.), Nymphoides Ség., Ornduffia Tippery & Les, and Villarsia Vent. Menyanthes and Nephrophyllidium are found only in the northern hemisphere, Liparophyllum, Ornduffia and Villarsia are restricted to the southern hemisphere, and Nymphoides has a cosmopolitan (worldwide) distribution, with centers of diversity in Africa, Australia, India, and the Americas. Menyanthes and Nephrophyllidium are monotypic (having only one species each), Liparophyllum has eight species, Ornduffia has seven, Villarsia has three, and Nymphoides has about 40-50 species. Taxonomic changes based on recent morphological and molecular evidence have segregated most of the species formerly included in Villarsia into Liparophyllum and Ornduffia.

Morphology
    Vegetative - All species of Menyanthaceae are aquatic, meaning that they spend all or most of their life cycle at least partly underwater. Five genera are predominantly emergent plants that have an erect inflorescence. Nymphoides, the most widespread genus, consists mostly of floating-leaved plants in which the leaves help keep the flowers above the water surface. I study the mechanism through which the floating leaf and inflorescence apparatus arose from a wetland ancestor.
    Reproductive - In addition to their diversity in vegetative morphology, species of Menyanthaceae have a diverse array of reproductive systems, including hermaphroditism, gynodioecy, and dioecy. Heterostyly also occurs in all genera, with the majority of species being heterostylous. Only four species of Menyanthaceae are dioecious, and these all belong to the genus Nymphoides. Using a phylogenetic framework, I plan to infer the directionality of conversions to and from different reproductive systems, and address the evolutionary forces promoting changes in floral morphology.

ITS secondary structure

With my advisor I have developed a method to encode secondary structure of the internal transcribed spacer (ITS), a region of DNA interspersed with ribosomal RNA genes. The secondary structure of ITS regions (as transcribed RNA) has been shown to be conserved across distantly related groups, and we were able to use secondary structure data to reconstruct a phylogeny of Menyanthaceae that closely matched the tree derived from nucleotide sequences of ITS and two chloroplast regions.
    The method and results are published in:
Tippery, N.P. and D.H. Les. 2008. Phylogenetic analysis of the internal transcribed spacer (ITS) region in Menyanthaceae using predicted secondary structure. Molecular Phylogenetics and Evolution 49: 526-537. [ abstract ]