Phylogeny of the Linnaea clade: Are Abelia and Zabelia closely related?

Phylogenetic investigations based on molecular and morphological data have improved our understanding of Dipsacales phylogeny dramatically over the past 20 years. The Linnaea clade, however, has mostly been neglected and Zabelia has rarely been included in previous studies. We present the results of a molecular investigation including nine Abelia and five Zabelia species based on nuclear (ITS) and plastid (trnK, matK, atpB-rbcL, trnL-F) sequence data using maximum parsimony, Bayesian inference, and maximum likelihood. Our results indicate that Abelia is paraphyletic and possibly polyphyletic. The genus falls apart into a Mexican clade, corresponding to Abelia section Vesalea, and an Asian clade (excluding A. spathulata), corresponding to Abelia section Abelia. A close relationship between Zabelia and other members of the traditional Linnaea clade is not recovered by our analyses. Instead, Zabelia is associated with either the Morina or the Valeriana clade. Support for a monophyletic Linnaea clade without Zabelia is strong.

Graphical abstractDownload full-size imageResearch highlights► Traditional Linnaea clade s.l. (Linnaeaceae sensu Backlund and Pyck, 1998; Linnaeeae sensu Donoghue et al., 2001) is paraphyletic, Linnaea clade s.s. is monophyletic. ► Abelia is paraphyletic (and possibly polyphyletic) with Mexican Abelia species (Abelia section Vesalea) forming a monophyletic group and most likely the first diverging lineage of the Linnaea clade s.s. ► Asian Abelia species (Abelia section Abelia) are paraphyletic. ► Zabelia is monophyletic but not closely related to Abelia. ► Kolkwitzia amabilis and Dipelta are sister groups.