Untangling the reticulate history of species complexes and horticultural breeds in Abelia (Caprifoliaceae)

Background and Aims The genetic and morphological consequences of natural selection and selective breeding are explored in the genus Abelia. The genus consists of ornamental shrubs endemic to China, which have been bred to create attractive and diverse cultivars. Methods DNA fingerprinting (AFLP) and DNA sequence data are used to investigate the genetic diversity among 46 accessions of Abelia (22 natural taxa and 24 horticultural breeds). In the cultivated varieties these data are used to explore taxon boundaries, hybridisation and backcrossing. The genetic analysis dataset is also used to investigate morphological variation within natural species complexes and subsequently to inform a taxonomic treatment. Key ResultsAbelia comprises five species: A. forrestii, A. schumannii, A. macrotera, A. uniflora and A. chinensis and has a total of 11 varieties. Abelia uniflora and A. macrotera do not occur in sympatry and are disjunctly distributed to the east and west of the A. chinensis distribution range. Abelia chinensis is widespread in eastern China and creates hybrids and introgressive taxa, including A. uniflora, along the contact zones with the previous taxa. Abelia `Maurice Foster' is a horticultural variety collected from wild stocks in Sichuan (China). Bayesian clustering methods (inferred in STRUCTURE based on AFLP data) indicate admixture between A. macrotera and A. schumannii in this variety. Hybridization probably occurred in the wild where these progenitor taxa co-occur and naturally form hybrids. AFLP results also reveal that a few diagnostic morphological characters such as sepal number or inflorescence structure were transferred between natural species and this is mirrored by taxa such as in Abelia `Saxon Gold' and A. forrestii. Conclusions Studying both natural and cultivated species from the same group has helped understanding both differentiation mechanisms and how to improve cultivated plants in the future by studying which morphological characters are transferred between species and which taxa may already have arisen through hybridisation.