The South American radiation of Lepechinia (Lamiaceae): Phylogenetics, divergence times and evolution of dioecy

Lepechinia (Lamiaceae) is a diverse and widespread genus that is important in indigenous New World culture. We present a phylogenetic analysis of 72 accessions representing 31 species of Lepechinia using data from three plastid (trnL-F, ycf1, ycf1-rps15 spacer) and four nuclear [internal transcribed spacer (ITS), external transcribed spacer (ETS), granule-bound starch synthaseI (GBSS)I, pentatricopeptide repeat region (PPR)-AT3G09060] DNA regions. Data were analysed using parsimony, maximum likelihood and Bayesian approaches. Divergence time estimation using BEAST shows Lepechinia had a mid/late Miocene origin, perhaps as a response to global cooling patterns. Cladogenesis in most South American Lepechinia is shown to have occurred within the past 5Myr, presumably as a response to climatic and orogenic events. Dioecy has arisen multiple times in Lepechinia, once in North America and at least twice in South America, and not necessarily involving gynodioecy as an intermediary step. Dioecy and gynodioecy are demonstrated to be associated with several floral characters, including flower size, number and colour.