Phylogenetic Relationships of Sambucus and Adoxa (Adoxoideae, Adoxaceae) Based on Nuclear Ribosomal ITS Sequences and Preliminary Morphological Data

Abstract

We inferred the phylogeny of Sambucus and Adoxa (Adoxoideae, Adoxaceae) based on nucleotide sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA, preliminary morphology, and a combination of the two data sets. Our morphological analysis implies that Adoxa is nested within Sambucus, based primarily on herbaceous habit and aspects of flower morphology. However, there is strong support for the monophyly of Sambucus based on ITS sequences and in the combined analysis, implying that morphological similarities shared by Adoxa and the two Australian species of Sambucus may have evolved independently. The relatively small variation in ITS sequences within Sambucus makes the sequences easy to align, but results in some ambiguity due to a limited number of informative characters. Nevertheless, there are several well-supported clades within Sambucus. Species with paniculate inflorescences (sect. Botryosambucus) form a well-supported clade, within which the red-fruited species are monophyletic. These results support the view that paniculate inflorescences and red fruits evolved independently in Sambucus and Viburnum. In all analyses S. ebulus and its relatives (sections Ebulus and Scyphidanthe) form a clade supported by valvate corolla lobes. Based on the combined analysis the first Adoxoideae may have been characterized by flowers with an equal number of carpels and perianth parts, and more-or-less separated style branches/stigma lobes. If so, reduction in the number of carpels and fusion of styles occurred within Sambucus.