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

Abstract

Abstract Tribe 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.