An expanded molecular phylogeny of Plumbaginaceae, with emphasis on <i>Limonium</i> (sea lavenders): Taxonomic implications and biogeographic considerations

Abstract

Plumbaginaceae is characterized by a history of multiple taxonomic rearrangements and lacks a broad molecular phylogenetic framework. <i>Limonium</i> is the most species-rich genus of the family with <i>ca</i>. 600 species and cosmopolitan distribution. Its center of diversity is the Mediterranean region, where <i>ca</i>. 70% of all <i>Limonium</i> species are endemic. In this study, we sample 201 <i>Limonium</i> species covering all described infrageneric entities and spanning its wide geographic range, along with 64 species of other Plumbaginaceae genera, representing 23 out of 29 genera of the family. Additionally, 20 species of the sister family Polygonaceae were used as outgroup. Sequences of three chloroplast (<i>trnL-F</i>, <i>matK,</i> and <i>rbcL</i>) and one nuclear (ITS) loci were used to infer the molecular phylogeny employing maximum likelihood and Bayesian analyses. According to our results, within Plumbaginoideae, <i>Plumbago</i> forms a non-monophyletic assemblage, with <i>Plumbago europaea</i> sister to <i>Plumbagella</i>, while the other <i>Plumbago</i> species form a clade sister to <i>Dyerophytum</i>. Within Limonioideae, <i>Ikonnikovia</i> is nested in <i>Goniolimon</i>, rejecting its former segregation as genus distinct from <i>Goniolimon</i>. <i>Limonium</i> is divided into two major clades: <i>Limonium</i> subg. <i>Pteroclados s.l</i>., including <i>L. </i>sect. <i>Pteroclados</i> and <i>L. anthericoides</i>, and <i>L. </i>subg. <i>Limonium</i>. The latter is divided into three well-supported subclades: the monospecific <i>L. </i>sect. <i>Limoniodendron</i> sister to a clade comprising a mostly non-Mediterranean subclade and a Mediterranean subclade. Our results set the foundation for taxonomic proposals on sections and subsections of <i>Limonium</i>, namely: (a) the newly described <i>L. </i>sect. <i>Tenuiramosum</i>, created to assign <i>L. anthericoides</i> at the sectional rank; (b) the more restricted circumscriptions of <i>L. </i>sect. <i>Limonium</i> (= <i>L. </i>sect. <i>Limonium</i> subsect. <i>Genuinae</i>) and <i>L. </i>sect. <i>Sarcophyllum</i> (for the Sudano-Zambezian/Saharo-Arabian clade); (c) the more expanded circumscription of <i>L. </i>sect. <i>Nephrophyllum</i> (including species of the <i>L. bellidifolium</i> complex); and (d) the new combinations for <i>L. </i>sect. <i>Pruinosum</i> and <i>L. </i>sect. <i>Pteroclados</i> subsect. <i>Odontolepideae</i> and subsect. <i>Nobiles</i>.