Molecular phylogenetics and new (infra)generic classification to alleviate polyphyly in tribe Hydrangeeae (Cornales: Hydrangeaceae)

Yannick De Smet,Marie-Stéphanie Samain,Carolina Granados Mendoza,Stefan Wanke,Paul Goetghebeur

doi:10.12705/644.6

Abstract

AbstractTribe Hydrangeeae of Hydrangeaceae currently contains nine morphologically diverse genera, many of which are well‐known garden ornamentals. Previous studies have shown eight of these genera to be phylogenetically nested within Hydrangea, rendering the latter polyphyletic. To clarify the phylogeny of tribe Hydrangeeae, the present study sequenced four chloroplast regions and ITS for an extensive set of taxa, including the type for all nine genera involved. The resulting phylogenetic hypotheses corroborate the polyphyly of Hydrangea. Since polyphyletic taxa are deemed unacceptable by both sides in the ongoing debate concerning the adherence to strict monophyly in biological classifications, a new (infra)generic classification for tribe Hydrangeeae is proposed. In order to create a stable, evolutionary informative classification a broader circumscription of the genus Hydrangea is proposed, to include all eight satellite genera of the tribe. Such treatment is considered highly preferable to an alternative where Hydrangea is to be split into several morphologically potentially unidentifiable genera. To facilitate the acceptance of the new classification proposed here, and in order to create a classification with high information content, the familiar generic names were maintained as section names where possible.

Highlights

Over the past few decades, rapid advances in DNA technologies have brought about an increase in the use of phylogenetic hypotheses in taxonomy
To facilitate the acceptance of the new classification proposed here, and in order to create a classification with high information content, the familiar generic names were maintained as section names where possible
Congruences and conflicts in tribe Hydrangeeae. — This study presents the most comprehensive phylogenetic hypothesis for tribe Hydrangeeae to date

Summary

Introduction

Over the past few decades, rapid advances in DNA technologies have brought about an increase in the use of phylogenetic hypotheses in taxonomy (e.g., phylogenetic systematics; Hennig, 1966). The school of evolutionary systematics advocates a classification system with a high information content (Stuessy, 1987; Van Wyk, 2007; Hörandl, 2010; Mayr & Bock, 2002) and practicability (Brummit, 2002; Brickel & al., 2008), reflecting natural processes. In this philosophy, shared descent is viewed as an important character for grouping taxa, but an emphasis is placed on degrees of divergence and similarity between elements of a certain taxon (Hörandl & Stuessy, 2010). This group provides an interesting case study for solving complex classification problems due to the presence of (1) paraphyletic groups both at genus level and below, (2) a large polyphyletic assemblage, and (3) important horticultural representatives with very distinct morphology

Methods

Results

Conclusion