October 2010 to present, PhD study

This project focuses specifically on Chinese representatives of Hydrangea subsections Petalanthe, Asperae and Heteromallae. In the Hydrangea contribution to the Flora of China (which is based on the study of herbarium specimens), both authors disagree on the status of most of the taxa. The American author identifies three widespread, highly variable species (H. chinensis, H. aspera and H. heteromalla), whereas the Chinese author recognizes three species complexes with respectively four, five and seven species. In addition, both authors discuss many other taxa controversially, resulting in the discrepancy of 33 versus 18 Chinese taxa (with respectively 25 and 9 endemic species) in the same publication. Hence, the need for a thorough study of these taxa imposes itself in the light of the rapid deterioration of their habitats.

These three subsections are not closely related; hence, their similarly confusing taxonomy indicates an uncomprehended variation, likely the result of a comparably complex evolutionary history. Among and within Hydrangea taxa, many morphological characters vary continuously, probably reflecting adaptation to climatic and edaphic variation of the vast latitudinal and altitudinal ranges in China. This variability is also visible in ex situ collections, hindering correct identification. Detailed morphological and morphometric studies will examine this variation within a molecular framework, likely showing inconsistencies between the phylogenies and species boundaries on a morphological basis, indicating natural (multiple) hybridization.

Within this project we aim to elucidate phylogenetic relationships between Asian Hydrangea species and trace Hydrangea cultivars back to their wild origin, based on accessions from the ex situ Hydrangea collection of Ghent University and of Hydrangea-collectors, as well material which has been collected in China. For this purpose, molecular markers for phylogenetic construction at low taxonomic level are selected and tested. We will also unravel species boundaries and speciation processes of Chinese Hydrangea taxa, using an extensive sampling carried out on population level in two transects. This is accomplished by combining morphological, morphometric, cytological and molecular studies. This will be followed by a proposal to update the taxonomy and classification of Chinese Hydrangea, based on the study of fresh material and reflecting the phylogenetic relationships within the Hydrangea subsections Petalanthe, Asperae and Heteromallae. Field observations are also incorporated in the worldwide Red List of Hydrangea. For more information, see the Hydrangeaceae: Biodiversity & Conservation webpage.
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Relevant publications:
De Smet YVP, Granados Mendoza C, Wanke S, Goetghebeur P, Samain MS. (2015) Molecular phylogenetics and new generic classification to alleviate polyphyly in tribe Hydrangeeae (Hydrangeaceae, Cornales). Taxon 64 (4): 741-753.
De Smet YVP, Larridon I, Bauters K, Goetghebeur P, Samain MS. (2015) Re-discovering Hydrangea sargentiana, a taxon in need of conservation action. Acta Horticulturae 1087: 221-224.

Drs. Yannick De Smet
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