Phylogeny, Hybridization, and Evolution of Habit and Breeding System in Sidalcea and Eremalche (Malvaceae)

Abstract

Reconstructing the phylogeny of the western North American Sidalcea-Eremalche lineage provides an opportunity to study the evolution of different fundamental traits considered to play an important role in plant evolution. These plants display different life-history strategies, such as annual and perennial habit and hermaphroditic and gynodioecious breeding systems, enabling evolutionary investigation of these traits in a phylogenetic context. Difficult species delimitations have been suggested to be caused by hybridization in combination with polyploidy. Molecular phylogenetic analyses based on sequences of the chloroplast intron rpl16 and nuclear ribosomal DNA show that the genera are strongly supported as monophyletic sister lineages, and the polytomy in Sidalcea in both data sets likely represents a rapid radiation event. Coastal California is indicated as ancestral area for Sidalcea, in agreement with earlier biogeographical hypotheses. Hybridization hypotheses gained support from the chloroplast DNA data for the hexaploid Sidalcea lineage and for S. sparsifolia and S. pedata. Sidalcea section Annuae, including the annuals, represents a paraphyletic assemblage. The shift between annual and perennial habit must have happened at least four times, but reversals to perenniality appear unlikely. At least five reversals from the gynodioecious to the hermaphroditic condition are inferred, possibly due to population bottlenecks in some lineages.