Systematic Botany (2004), 29(3): pp. 716±736 q Copyright 2004 by the American Society of Plant Taxonomists Morphological Evolution and Systematics of Synthyris and Besseya (Veronicaceae): A Phylogenetic Analysis LARRY HUFFORD2 and MICHELLE MCMAHON1 School of Biological Sciences, Washington State University, Pullman, Washington 99164-4236 1Present address: Section of Ecology and Evolutionary Biology, Division of Biological Sciences, University of California, Davis, California 95616 2Author for correspondence (
[email protected]) Communicating Editor: Wendy B. Zomlefer ABSTRACT. Phylogenetic analyses are used to examine the morphological diversity and systematics of Synthyris and Besseya. The placement of Synthyris and Besseya in Veronicaceae is strongly supported in parsimony analyses of nuclear ribosomal ITS DNA sequences. Parsimony and maximum likelihood (ML) criteria provide consistent hypotheses of clades of Synthyris and Besseya based on the ITS data. The combination of morphological characters and ITS data resolve additional clades of Synthyris and Besseya. The results show that Synthyris is paraphyletic to Besseya. In the monophyletic Synthyris clade, Besseya forms part of a Northwest clade that also includes the alpine S. canbyi, S. dissecta,andS. lanuginosa and mesic forest S. cordata, S. reniformis, S. platycarpa,andS. schizantha. The Northwest clade is the sister of S. borealis. An Intermountain clade, comprising S. ranunculina, S. laciniata, S. pinnati®da,andS. missurica, is the sister to the rest of the Synthyris clade. Constraint topologies are used to test prior hypotheses of relationships and morphological similarities. Parametric bootstrapping is used to compare the likelihood values of the best trees obtained in searches under constraints to that of the best tree found without constraints.