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Higher-Level Relationships and Major Lineages of Lessingia (Compositae, Astereae) Based on Nuclear rDNA Internal and External Transcribed Spacer (ITS and ETS) Sequences

Abstract The apparent recency of diversification of Californian Lessingia (Compositae, Astereae) makes the genus a particularly interesting group for evolutionary investigation. Here we focus on the major evolutionary lineages within Lessingia (sensu Lane 1992) and the higher-level relationships of the genus and presumed close relatives using sequence data from the 18S–26S nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) region and the 3’ end (561–563 bp) of the external transcribed spacer (ETS). We present new 3‘ETS primers that are useful across Astereae and examine the phylogenetic utility of the 3‘ETS in Lessingia and close relatives. In Lessingia, the 3‘ETS region appears to have evolved up to 1.4 times more rapidly by nucleotide substitution than has the ITS region. Our results show that data from the ETS greatly augments data from the ITS region; the combined data set yields the best resolved and best supported molecular trees for Lessingia. These topologies lead us to five conclusions regarding the phylogenetic relationships of Lessingia (sensu Lane 1992) and closely related genera: (1) Lessingia may not be monophyletic when Benitoa is included within the genus, (2) among the taxa sampled, Benitoa and Hazardia appear to be the closest living relatives of Lessingia s. s. and L. filaginifolia (= Corethrogyne), (3) a sister group relationship exists between the radiate, perennial L. filaginifolia (= Corethrogyne) and the discoid, annual members of the genus (Lessingia s. s.), (4) different corolla coloration (pink/white vs. yellow) diagnoses the two major clades of Lessingia s. s., and (5) the “yellow group” of lessingias comprises three distinct, morphologically diagnosable, lineages which span the currently accepted circumscriptions of two taxa (L. lemmonii and L. glandulifera). Communicating Editor: Kathleen A. Kron